14859695 medical-gas-pipeline-systems

Medical gas
pipeline systems
Design, installation,
validation and verification
Health Technical Memorandum 2022

London: The Stationery Office

© Crown copyright 1997. Published with permission of NHS Estates,
an Executive Agency of the Department of Health,
on behalf of the Controller of Her Majesty’s Stationery Office.

Applications for reproduction should be made in writing to
The Copyright Unit, Her Majesty’s Stationery Office,
St Clements House, 2–16 Colegate, Norwich NR3 1BQ.

First published 1997

ISBN 0-11-322067-7

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About this series

Health Technical Memoranda (HTMs) They are applicable to new and existing
give comprehensive advice and sites, and are for use at various stages
guidance on the design, installation and during the inception, design,
operation of specialised building and construction, refurbishment and
engineering technology used in the maintenance of a building.
delivery of healthcare.

Executive summary

An MGPS is installed to provide a safe, convenient and This volume of Health Technical Memorandum
cost-effective system for the provision of medical gases to (HTM) 2022 looks at issues of design, installation,
the clinical and nursing staff at the point of use. It reduces verification and validation. It covers the user requirements
the problems associated with the use of gas cylinders such for flow, pressure and diversity and gives technical
as safety, porterage, storage and noise. guidance on the design, installation and accommodation
of plant and medical pipeline distribution systems. In
The guidance given in this HTM should be followed for all addition, this volume describes the procedures to be
new installations, and for refurbishment or upgrading of carried out before a medical gas pipeline system (MGPS)
existing installations. can be taken into use. The tests to be carried out at each
stage of the installation programme are set out, together
It is not necessary to apply the guidance retrospectively with requirements for personnel, instrumentation and
unless patient or staff safety would be compromised. In documentation required.
this case, the guidance given in this HTM should be
followed. This volume is intended for use by designers, installers,
manufacturers, operational managers, engineers, quality
Existing installations should be assessed for compliance controllers, technicians, finance officers and other
with this HTM. A plan for upgrading the existing system professionals involved in the day-to-day running of an
should be prepared, taking account of the priority for MGPS.
patient safety. Managers will need to liaise with medical
colleagues and take account of other guidance published The primary objective of this volume is to ensure the
by the Department of Health in order to assess the system provision of safe and reliable MGPS and their efficient
for technical shortcomings. operation and use. This objective will only be achieved
if the medical and nursing users and estates staff
participate in the introduction of an operational policy
designed to minimise the hazards likely to arise from
misuse of the system.

Contents

1.0 Scope page 7 4.49 Medical air 400 kPa
1.1 Guidance in this document 4.49 General
1.6 Other guidance 4.55 Pressure requirements
1.7 Design installation and testing 4.59 In-patient accommodation
4.63 Surgical air 700 kPa
2.0 General principles page 8 4.63 Flow and pressure requirements for
2.1 General statement 700 kPa surgical air system
2.8 Quality requirements for medical gases and air 4.66 Diversity
2.11 Odour and moisture 4.68 System capacity
2.11 Odour 4.69 Terminal units intended for equipment
2.13 Moisture testing
2.16 Pipeline distribution system design 4.71 Vacuum
2.19 Safety 4.71 In-patient accommodation
2.24 Installation/supply of equipment/maintenance 4.75 Operating departments
2.25 Modifications 4.82 Intensive therapy unit, coronary care unit
2.28 Removal of pipework and neonatal unit
2.29 Validation and verification
2.30 General fire precautions 5.0 System design – General page 35
2.30 General 5.1 Cylinder manifold installation
2.32 Fire detection system 5.1 General
2.33 Electricity supply to medical gas installations 5.9 Pressure control
2.33 General 5.14 Manifold monitoring and indicating system
2.40 Earthing 5.16 Manifold control unit
2.42 Installation of electrical cables 5.17 Manifold monitoring
2.45 Electrical wiring in plantrooms 5.18 Manifold indication unit
2.49 Electrical supply pendants 5.19 Alarm signal status unit
2.49 Ceiling pendant fittings – rigid, multi- 5.23 Emergency reserve supply
purpose type 5.23 General
2.50 Bed head trunking/walling system 5.31 Emergency reserve supplies for manifold
installations
3.0 Provision of terminal units page 15 5.33 Emergency reserve supply for air compressors/liquid
3.1 General oxygen/oxygen concentrators (PSA)
3.18 Terminal units for nitric oxide, oxygen/carbon 5.34 Location
dioxide mixture 5.35 Design
3.19 Nitrogen for surgical tools
6.0 System design – Oxygen supplies page 42
4.0 Gas flow page 21 6.1 Bulk liquid oxygen systems and vacuum insulated
4.1 General evaporator (VIE)
4.10 Gas flow 6.1 General
4.10 Terminal unit flows 6.5 System sizing
4.13 Pipeline flows 6.9 Equipment description
4.21 Oxygen 6.10 Standby oxygen facility
4.21 In-patient accommodation 6.11 System layout
4.27 Hyperbaric oxygen chambers 6.12 VIE
4.28 Operating departments 6.15 Control piping and instrumentation
4.32 Intensive therapy and coronary care units 6.17 Pressure raising system
4.36 Maternity 6.19 Direct reading contents gauge and
4.40 Nitrous oxide telemetry systems
4.43 Nitrous oxide/oxygen mixtures 6.26 Control panel
4.47 Medical air 6.27 Sites for liquid oxygen storage
4.47 General 6.30 Operation
6.32 Standby system in use

1

Contents

6.35 Standby low 7.42 Activated carbon filter
6.36 Low line pressure 7.43 Bacteria filters
6.37 High line pressure 7.44 Pressure control
6.39 VIE filling 7.45 Test point
6.40 Maintenance 7.46 Safety valves
6.42 Standby oxygen facility 7.48 Traps and valves
6.45 Backup bulk liquid storage vessel 7.48 Automatic drainage traps
6.48 Liquid cylinder backup 7.50 Non-return valves
6.50 Compressed gas cylinder backup 7.51 Isolating valves
6.52 Emergency supply facility 7.52 Pressure indicators
6.58 Alarm signal status unit 7.53 Operating and indicating system
6.62 Liquid oxygen supplies 7.61 Plant control unit
6.62 General 7.64 Plant control indication
6.65 Liquid cylinder design 7.65 Compressor starter units
6.67 Liquid cylinder manifolds 7.66 Dryer control unit
6.69 Control panel 7.68 Plant status monitoring
6.71 Emergency compressed oxygen manifold 7.69 Plant indicator unit
6.72 Siting requirements 7.72 Alarm signal status unit
6.82 Liquid cylinder manifold sizing 7.77 Plant management
6.84 Refilling 7.78 Operating considerations
6.85 Alarm signal status unit 7.79 Synthetic air
6.89 Oxygen concentrator installations (PSA plant) 7.79 General
6.89 General 7.88 System description
6.94 Siting 7.95 Storage vessels
6.98 Plant configuration 7.95 Vessel summary
6.100 Compressors and vacuum pumps 7.96 Vessel operating pressure
6.102 Compressor noise 7.97 Main vessel capacity
6.104 Molecular sieves 7.98 Backup vessel capacity
6.105 Dryers 7.104 Vaporisation
6.106 Oxygen monitoring system 7.109 Medical oxygen flow control
6.107 Operating and indicating system 7.110 Surgical nitrogen flow control
6.111 Plant control unit 7.112 Control panel for the nitrogen and oxygen
6.115 Plant control indication supplies to the mixing panels
6.116 Compressor and vacuum starter units 7.116 Air mixing panels
6.117 Molecular sieve control unit 7.121 Buffer vessels
6.119 Plant status monitoring 7.124 Alarm signal status unit
6.120 Plant indicator unit 7.128 Emergency supply facility
6.124 Alarm signal status unit
6.129 Plant management 8.0 System design – surgical air 700 kPa page 86
8.1 General
7.0 System design – Medical air page 67 8.9 Cylinder manifold supply systems
7.1 Compressor systems for 400 kPa medical air 8.11 Compressor supply systems
7.1 General 8.13 Operating and alarm system
7.2 Quality 8.13 Cylinder manifold supply system
7.3 Siting 8.13 Manifold monitoring and indicator
7.7 Compressor noise system
7.9 Air intake 8.14 Manifold monitoring
7.10 Compressor types 8.15 Manifold indicator unit
7.13 Compressor lubrication 8.16 Alarm signal status unit
7.21 After-coolers 8.20 Compressor supply system
7.22 Receivers 8.21 Plant status monitoring
7.24 Air treatment and filtration 8.22 Plant indicator unit
7.24 General 8.25 Alarm signal status unit
7.25 Solid contaminants 8.30 Plant management
7.29 Water 8.31 Operating considerations
7.31 Oil 8.32 Simplex plant
7.39 Dryer controls
7.40 Dust filters

2

Contents

9.0 System design – medical vacuum supplies 12.0 Warning and alarm systems page 114
page 90 12.1 General
9.1 Medical vacuum supplies 12.7 Panel location
9.1 General 12.7 Central indicator panel
9.9 Siting 12.8 Repeater indicator panel location
9.11 Pump noise 12.9 Area warning and alarm panel location
9.13 Vacuum plant exhaust 12.10 System description
9.16 Efficiency 12.10 System components
9.18 Vacuum pumps 12.11 System layout
9.35 Pressure control 12.11 Central system
9.37 Valves 12.12 Area warning and alarm systems
9.39 Pressure regulation of vacuum system 12.13 General requirements
9.42 Vacuum indicators 12.13 Labelling
9.44 Electrical supply 12.14 Visual signals
9.45 Pump operating and indicating system 12.17 Audible signals
9.45 General description 12.18 Automatic re setting
9.49 Plant control unit 12.19 Temporary muting
9.53 Plant control indication 12.20 Continuous muting
9.54 Pump starter units 12.21 Electrical wiring
9.55 Plant status monitoring 12.22 System integrity
9.56 Plant status indicator unit 12.25 Relay condition
9.58 Alarm signal status unit 12.26 Mains power supply
9.62 Plant management 12.27 SELV/FELV power supply
12.30 Test facility
10.0 System design – anaesthetic gas scavenging 12.31 Warning and alarm system faults
systems page 100 12.31 General
10.1 Anaesthetic gas scavenging systems 12.32 Line fault
10.1 General 12.33 Communication/wiring fault
10.10 Background 12.34 Mains power failure
10.18 Sources of pollution and provision of AGS 12.35 Standby battery
systems 12.36 Legend
10.32 AGS system design 12.37 Indicator panel requirements for all systems
10.32 General 12.37 Indicators
10.35 Active and passive systems 12.40 Labelling
10.40 General design requirements 12.41 Construction
10.46 Safety criteria 12.48 Remote audible sounder
10.48 Performance criteria 12.49 Central indicator panel requirements
10.51 Flow diversity 12.49 Displays
10.52 Discharge outlet 12.50 Mute functions
10.53 Duplex system 12.53 Panel legend and display
10.54 Plant control indication 12.54 Repeater indicator panel requirements
12.54 Displays
11.0 System design – Nitric oxide page 109 12.55 Mute functions
11.1 Nitric oxide pipeline installations 12.58 Panel legend and display
11.1 Introduction 12.59 Area warning and alarm panel
11.5 Design considerations 12.54 Displays
11.10 Provision of terminal units, valves and area 12.60 Mute functions
valve service units (AVSUs) 12.62 Panel legend and display
11.14 Manifold 12.63 Location
11.22 Provision of valves
11.24 Provision of AVSUs 13.0 Pipeline installation page 126
11.28 Pipeline distribution 13.1 Accommodation of pipes
11.29 Identification 13.9 Pipeline materials
11.30 Alarm systems 13.10 Quality
11.32 Nitric oxide – risk assessment for COSHH 13.12 Pipes
compliance 13.14 Other fittings
11.38 Validation and verification 13.15 Cleaning
13.15 Pipes

3

Contents

13.16 Pipe joining fittings 15.43 Cross-connection
13.18 Pipeline jointing 15.44 Requirements for pipeline system tests
13.18 General 15.44 Leakage from total compressed medical
13.27 Jointing methods gas systems
13.30 Pipe preparation 15.49 Leakage into total vacuum systems
13.31 Use of N2 internal inert gas shield 15.50 Closure of area valve service units
13.31 Application 15.54 Zoning of AVSUs and terminal unit
13.33 Safety identification
13.34 Control cylinders 15.58 Cross-connection
13.35 Other installation processes 15.63 Flow and pressure drop at terminal
13.36 Inspection of joins units
13.37 Internal cleanliness 15.64 Mechanical function of terminal units
13.38 Penetration 15.65 Gas specificity of terminal units
13.39 Capping 15.66 NIST connectors
13.40 Removal of flux residues and oxides 15.68 Performance tests of the pipeline
13.45 Purging with the working gas system
13.46 Pipe supports 15.72 Functional tests of supply systems
13.52 Identification of pipelines 15.74 Pressure safety valves
13.54 Pipeline fittings 15.76 Warning systems
13.54 General 15.78 Verification of as-fitted drawings
13.55 Ceiling pendant fittings rigid, multi-purpose 15.79 Filling with medical air
type 15.86 Purging and filling with specific gases
13.61 Flexible pendant fitting 15.88 Quality of compressed medical gas systems
13.62 Bed head trunking/walling system 15.88 General
13.67 Shut-off valves 15.95 Particulate matter
13.68 Provision of valves 15.97 Oil
13.70 Area valve service units (AVSUs) 15.99 Water
13.75 Provision of AVSUs 15.101 Carbon monoxide
13.75 General 15.102 Carbon dioxide
13.79 Labelling 15.104 Nitrogen
13.81 Pressure sensors 15.105 Pipeline odour
13.82 Pressure gauges 15.106 Gas identification
13.83 Test points 15.111 Requirements before a MGPS system is taken to
13.84 Emergency inlet port use
13.86 Line pressure alarms and safety valves 15.111 General
15.115 Operational policy
14.0 Accommodation page 138 15.116 Cylinder storage and handling
14.1 Design and construction of plantrooms 15.117 Removal of construction labels
14.1 Location of plantrooms 15.118 Anaesthetic gas scavenging systems
14.7 Access 15.118 General
14.11 Construction and layout of manifold rooms 15.123 Performance tests: disposal systems
14.14 Heating and ventilation of plantrooms 15.123 Powered device
14.22 Lighting 15.125 Pipework/ductwork installation
14.23 Noise control 15.127 Performance testing
15.139 Receiving system
15.0 Validation and verification page 141 15.134 Performance efficiency
15.1 General 15.140 Methods and procedures for validation and
15.14 Summary of tests verification of medical gas pipeline systems
15.14 Tests and checks on the pipeline carcass 15.140 General
15.15 Test on the pipeline system 15.146 Labelling and marking
15.16 Tests before use 15.148 Sleeving and supports
15.17 General requirements for testing 15.150 Leakage
15.17 General 15.154 Cross-connection
15.29 Modifications,extensions or repairs to 15.157 Leakage from compressed medical gas
existing systems systems
15.37 Requirements for pipeline carcass tests 15.160 Leakage into vacuum system
15.37 Labelling and marking 15.163 Closure of AVSUs
15.38 Sleeving and supports 15.166 Zoning of AVSUs
15.39 Leakage 15.170 Cross-connection

4

Contents

15.174 Functional tests of terminal units
15.176 Performance tests of the pipeline
system
15.179 System supply tests
15.184 Safety valve inspection
15.187 Warning system tests
15.191 Verification of drawings
15.193 Filling with medical air
15.197 Purging and filling with specific gas
15.200 Tests for quality
15.203 Tests for gas identity
15.206 System taken into use

Appendix A – Testing, commission and filling for use:
Forms to be completed during testing and
commissioning of piped medical gases systems
page 173

Appendix B – Gas pressure variation with
temperature page 191

Appendix C – Pressure drop test device page 192

Appendix D – Membrane filter test device page 194

Appendix E – Equipment for contaminant testing
page 196

Appendix F – Equipment for gas identification
page 197

Appendix G – Procedures for measuring the design
flow of vacuum plant page 199

Appendix H – Procedure for measuring pipeline
volume page 200

Appendix J – Pressure loss data page 202

Appendix K – Pressure regulation for 400 kPa
(medical gases and medical air) and 700 kPa systems
(surgical air) page 208

References page 211

Other publications in this series page 213

About NHS Estates page 214

5

1.0 Scope

Guidance in this document Other guidance

1.1 Guidance in this volume of Health Technical 1.6 Guidance on the provision of MGPS is given in the
Memorandum (HTM) 2022 covers piped medical gases, Health Building Notes.
medical compressed air and medical vacuum installations,
and applies to all medical gas pipeline systems (MGPS)
installed in healthcare premises.
Design, installation and testing
1.2 An MGPS is installed to provide a safe, convenient
1.7 This volume of HTM 2022 deals with the issues
and cost-effective system for the provision of medical
involved in the design, installation and testing of an
gases to the clinical and nursing staff at the point of use.
MGPS.
It reduces the problems associated with the use of gas
cylinders such as safety, porterage, storage and noise.
1.8 The standard specification, Model Engineering
Specification C11, supports this HTM. C11 provides details
1.3 The guidance given in this volume should be
of the extent of the works required and is a procurement
followed for all new installations and refurbishment or
specification.
upgrading of existing installations.

1.9 Whenever appropriate, British Standard
1.4 It is not necessary to apply the guidance
specifications should be used.
retrospectively unless patient or staff safety would be
compromised. In this case, the guidance given in this
volume should be followed.

1.5 Existing installations should be assessed for
compliance with this volume. A plan for upgrading the
existing system should be prepared, taking account of the
priority for patient safety. Managers will need to liaise
with medical colleagues and take account of other
guidance published by the Department of Health in order
to assess the system for technical shortcomings.

7

2.0 General principles

General statement

2.1 An MGPS is designed to provide a safe and effective method of
delivering the required medical gas from the source of supply through a
pipeline system to the patient via a terminal unit.

2.2 Each medical gas must be supplied from a separate system, and it is
essential that all parts of each system are gas specific to ensure that there is no
possibility of cross-connection between any system. A schematic diagram of a
typical MGPS is shown in volume 1 of this HTM, ‘Operational management’
(Figure 1).

2.3 Systems for dental air and vacuum are covered in HTM 2022
Supplement 1, ‘Dental compressed air and vacuum systems’, since the
requirements are different. However, where anaesthetic gases are administered
in dental departments, the guidance given in this HTM should be followed.

2.4 During the installation stage, extensive tests are carried out to verify
that there is no cross-connection.

2.5 Where medical air 400 kPa is to be used for testing surgical tools and
other medical equipment, this requirement should be considered at the design
stage to ensure that sufficient capacity is available. Details of design flows are
given in Chapter 4 “Gas flow”.

2.6 MGPS should not be used to supply pathology departments, general
workshops or mechanical services. The 400 kPa medical air system may,
however, be extended to those departments where respiratory equipment or
surgical tools are serviced, such as in sterile disinfection units (SDUs), electronic
and biomedical equipment (EBME) workshops etc. In such cases only, to
facilitate the testing and checking of operation of equipment for the different
medical gases, all terminal units (excluding vacuum) may be connected to the
medical air supply and be provided with simplified alarm facilities and labelled
accordingly.

2.7 Separate installations should be provided for pathology and general
laboratories and workshops, although it is recommended that they are
constructed to the same specification as MGPS. They should not be provided
with medical gas terminal units. Piped medical vacuum systems are not
recommended for infectious disease units.

Quality requirements for medical gases and air

2.8 Medical gases supplied from cylinder or liquid sources comply with the
appropriate sections of the current edition of the European Pharmacopoeia (Ph
Eur). There is currently no Ph Eur for site-generated medical air and oxygen
pressure swing adsorber (PSA) systems. The quality specification for medical air
is as given in Table 1.

8


2.9 The introduction of the new Ph Eur for medical air will be effective
from 1998 and therefore medical air will need to comply with this new
specification. The Ph Eur also specifies validation protocols which will need to
be adopted.

2.10 The quality of piped medical compressed air, the particulate content,
dryness and concentration of impurities, should comply with the requirements
for maximum concentrations given in Table 1, which is based on the
specification for breathing air in BS EN 132:1991. Information on testing
procedures is given in Chapter 15, ‘Validation and verification’.

Table 1 Quality specification for medical air
(for the requirement for dental compressed air refer to the relevant
supplement)

Parameter Specification

Oxygen 20.9 +/–1.0%

Nitrogen 78% by inference

Particulate contamination Practically free from visible
particles in a 75 l sample

Water content
– see paragraph 2.13 115 vpm (0.095 mg/l)
(equivalent to dewpoint
–40ºC at atmospheric
pressure)

CO 5 ppm v/v

CO2 500 ppm v/v

Oil content (droplet or mist) <0.5 mg/m3

Odour
– see paragraph 2.11 none

Note: Similar values apply to other medical gases; see relevant paragraph(s) in
appropriate Ph Eur monograph.

Odour and moisture

Odour

2.11 The odour threshold of measurable particulate matter is approximately
0.3 mg/m3.

2.12 Some elastomeric materials, such as those commonly used in flexible
hose, may have a distinctive odour, particularly when new. Extensive tests
have shown that the agents likely to be responsible for the odour are present
only in minute (parts per billion) quantities and are considered to be of no
toxicological significance. Clearly the odour should not be nauseous.

Moisture

2.13 Similarly, those elastomeric materials have been shown to desorb
minute quantities of moisture into the gas stream. The amounts of moisture

9


are very small but, on initial testing, may result in moisture levels slightly in
excess of 0.095 mg/l. These slightly raised levels of moisture may persist on
initial testing for several months. Extensive tests have shown that these slightly
raised levels are of no consequence, and reduce following purging with the
working gas or use of the system.

2.14 Bacteria filters should be included in medical compressor systems to
reduce the risk of delivering spores or other infectious material to vulnerable
patients.

2.15 Micro-organisms can penetrate a bacteria filter if the material is wet.
Therefore it is essential that the dryness of the medical air supplied to a
bacteria filter is checked regularly (at least every three months) at the test
point, using the test equipment specified in Chapter 15.

Pipeline distribution system design

2.16 The following general information is required in order to design an
MGPS:

a. schedule of provision of terminal units;

b. design flow rates and pressure requirements at each terminal unit;

c. diversified flows for each section of the pipeline system;

d. total flow.

2.17 Guidance on deriving and calculating the above parameters is given in
chapters 3 and 4 of this volume.

2.18 The definition of “departments”, which may comprise several wards,
treatment rooms etc, should be agreed at the project design stage to avoid
confusion.

Safety

2.19 The safety of MGPS is dependent on four basic tenets:

a. identity;

b. adequacy;

c. continuity;

d. quality of supply.

2.20 Identity is assured by the use of gas-specific connections throughout
the pipeline system, including terminal units, connectors, etc, and by the
adherence to strict testing and commissioning procedures of the system.

2.21 Adequacy of supply depends on an accurate assessment of demands
and the selection of plant appropriate to the clinical/medical demands on the
system.

2.22 Continuity of supply is achieved by the specification of a system which
(with the exception of liquid oxygen systems which may include a secondary
vessel) have duplicate components, and by the provision of an adequate
emergency/reserve supply for all systems except vacuum; by the provision of
alarm systems, and by connection to the emergency power supply system.

10


Anaesthetic gas scavenging systems (AGSS) and high-pressure surgical air
systems are not considered as life-support systems and therefore duplicate
components and, in the case of the latter, an emergency/reserve supply
system, are not normally required. For operational reasons, reserve air
cylinders complete with regulators are usually available for surgical tools in
operating departments.

2.23 Quality of supply is achieved by the use of gases purchased to the
appropriate Ph Eur requirements or produced by plant performing to specified
standards, by the maintenance of cleanliness throughout the installation of
the system, and by the implementation of the various testing and
commissioning procedures.

Installation/supply of equipment/maintenance

The concept of the existing Quality 2.24 The installation of MGPS should only be carried out by specialist firms
Assurance BSI Scheme schedule QAS registered to BS EN ISO 9000 with scope of registration appropriately defined.
3720.1/206./A1 is currently under
review. Further guidance will be given
when appropriate.
Modifications

2.25 Special precautions are required when existing installations are to be
modified or extended to ensure that all sections of the pipeline system
remaining in use are not contaminated, and that the supply to patients is not
compromised. The section to be modified should be physically isolated from
the section in use. Closure of isolating valves is insufficient for this purpose.
Where area valve service units (AVSUs) have been installed the blanking
spades should be used. This isolation procedure is not required when work is
to be carried out on individual terminal units.

2.26 Modification of existing systems may be detrimental to the overall
performance of the system. In the case of older systems there may be
insufficient capacity to permit the system to operate safely with the flows
typically encountered in use today.

2.27 Any work involving alteration, extension or maintenance work on an
existing system should be subject to the permit-to-work procedure (see the
‘Operational management’ volume of this HTM).

Removal of pipework

2.28 Removal and cutting out of redundant medical gas pipelines and
equipment can present as great a hazard to patient safety as any other
modification. All such removal, including cutting into existing pipelines,
capping off and removal of redundant pipeline and equipment, should
only be carried out by specialist medical gases contractors. It should not be
carried out by demolition contractors.

Validation and verification

2.29 The objective of validation and verification is to ensure that all the
necessary safety and performance requirements of the MGPS will be met.
Validation and verification procedures will be required for new installations,

11


additions to existing installations and modifications to existing installations. The
scope of work will dictate the specific programme required. This is described in
more detail in Chapter 3, “Provision of terminal units”.

General fire precautions

General

2.30 The siting and general structural principles for the design of liquid
oxygen storage accommodation are given in Chapter 4 “Liquid oxygen
supplies and VIEs” and the requirements for plantrooms and gas manifold
rooms in Chapter 14 “Accommodation”.

2.31 Guidance on cylinder storage and handling is given in the ‘Operational
management’ volume of this HTM.

Fire detection system

2.32 Smoke or heat detector heads should be installed in the plantrooms,
medical gases manifold rooms and (when internal) medical gases cylinder
stores in any hospital having a fire detection system in accordance with HTM
82 ‘Firecode alarm and detection systems’.

Electricity supply to medical gas installations

General

2.33 The whole of the electrical installation should be carried out in
accordance with the extant edition of the IEE Regulations for Electrical
Installations.

2.34 The electricity supply to medical gas installations should be taken from
separate circuits from a distribution board which is an “essential” board fed by
the emergency generator system. This should also apply to the medical gas
alarms. Reference should be made to HTM 2011 ‘Emergency electrical
services’.

2.35 Care is required when selecting pipeline routes to prevent the pipes
coming into contact with electric cables and wiring, and to minimise the risk of
electric shock in the event of a fault on adjacent cables.

2.36 The final connection to any equipment, for example alarm panels or
control panels, should be made via an unswitched fused connection unit.

2.37 In the event of power failure or interruption, all systems should
continue to operate exactly as before the interruption occurred. For example,
except for automatic cycling compressors, dryers, pumps etc, the same
compressor and dryer (or vacuum pump) set should be on-line, and for
manifold systems the same bank should be running.

2.38 All electrical systems, including plant control systems, should be
designed in accordance with EMC Directives to reject spurious radio frequency
(RF) or mains noise typically occurring in hospitals, examples being diathermy

12


equipment and current spikes caused by plant start-up. Reference should be
made to HTM 2014 ‘Abatement of electrical interference’.

2.39 These systems should also be compatible with emergency electrical
supply systems which may be either non-interruptible or interruptible with
variable changeover delays.

Earthing

2.40 Pipelines should be bonded to the consumer’s earth terminal as
required by Regulation 413-2 of the IEE Regulations. This bonding should be
made as near as possible to the point at which the pipeline enters the building
from the plant. The size of the bonding conductor should be in accordance
with Table 54f of the Regulations. The pipelines should not themselves be
used for earthing the electrical equipment.

2.41 Flexible pipeline connections between the compressors or vacuum
pumping plant and the fixed pipelines should be bonded across to comply
with this requirement. Flexible connections in the fixed pipelines should not
normally be used, but if they are specially approved they should be similarly
bonded across.

Installation of electrical cables

2.42 Distribution pipelines should preferably be physically separated from
the metal sheath and armour of electric cables, as well as from metal
conduits, ducts and trunking and bare earth-continuity conductors associated
with any electric cables which operate at low voltage or above. Reference
should be made to HTM 2007 ‘Electrical services: supply and distribution’.

2.43 When physical separation is impracticable, or where there might be
contact with extraneous metal work, for example, where the pipes are carried
in metal partitions or where terminal units are mounted on metal bed-head
units, the pipelines should be effectively bonded to the metal work in
accordance with Regulations 525-10 of the IEE Regulations.

2.44 Where piped gases and electric wiring are enclosed in a boom, gas
control panel or other similar enclosure, the wiring should be carried in
separate conduit or trunking so that it cannot come into direct contact with
the piped gas installation. Where this is not possible, the wiring should be
secured in the most effective manner possible, clear of the medical gas pipes.
The cables should comply with IEE Regulation 523-17.

Electrical wiring in plantrooms

2.45 All electrical wiring in these rooms should be carried out using MICS
cable or cable of the type indicated in IEE Regulation 523-17, with adequate
protection against mechanical damage.

2.46 Fire-resistant cable conforming to BS 6387, PVC armoured cables, and
single insulated cables in conduit may also be used.

2.47 Each compressor, vacuum pump and manifold should be supplied from
a separate sub-circuit.

2.48 Metal-clad sockets, connection units and switches should be used in
plantrooms; plastic fittings are not appropriate.

13


Electrical supply pendants

Ceiling pendant fittings – rigid, multi-purpose type

2.49 The construction should provide segregation of low voltage, functional
extra-low voltage (FELV) electrical services by means of flexible partitions or
conduit, as appropriate. Access to “live” components should be via panels
which are removable by means of tools only.

Bed-head trunking/walling system

2.50 These fittings should generally be in accordance with HTM 2015
‘Bedhead services’. Separate compartments should be provided for electrical
services, nurse call/radio etc and medical gas pipelines.

14

3.0 Provision of terminal units

General

3.1 A typical schedule of provision of terminal units is given in Table 2.
Medical treatment policy is evolutionary, and therefore the project team
should review the requirements for individual schemes.

3.2 Terminal units should be mounted in positions which give the shortest
practicable routes for flexible connecting assemblies, between the terminal
unit and apparatus. Terminal units may be surface or flush mounted. They
may also be incorporated with electrical services, nurse call systems and TV
and radio audio services, in proprietary fittings such as bedhead trunking, wall
panel systems and theatre pendant fittings, etc. Refer also to HTM 2015
‘Bedhead services’.

3.3 When planning the installation of theatre pendant fittings, the location
of the operating luminaire and other ceiling-mounted devices should be taken
into consideration. When the operating room is provided with an ultra-clean
ventilation (UCV) system, it may be more practicable (and cost-effective) to
have the services (both medical gas and electrical) incorporated as part of the
UCV system partial walls.

3.4 The following installations are strongly deprecated:

a. floor-mounted terminal units;

b. vacuum systems in which body or other fluids are drawn through a
fixed pipeline connecting a terminal unit or other connector to a
remote vacuum jar.

3.5 All terminal units should conform to BS 5682:1984 (1992). Terminal
units intended for installation with the socket axis horizontal, ie wall mounted,
include a non-swivel device so that directly connected equipment such as flow
meters remain vertical; terminal units intended for installation with the socket
axis vertical, for example in certain types of pendant, do not include a
non-swivel device. Secondary locks are no longer included in terminal units.

Reference should be made to 3.6 An anaesthetic gas scavenging (AGS) terminal unit should be provided
EL(96)33 covering publication advice whenever nitrous oxide is available for anaesthetic procedures. In recovery
on the implementation of the Health areas, when nitrous oxide is not provided, where there is no primary source of
& Safety Commission’s ‘Occupational anaesthetic gas pollution and/or where nitrous oxide is used for analgesic
Exposure Standards for Anaesthetic purposes only, no anaesthetic gas scavenging system (AGSS) is required.
Agents’ published by the Department Where nitrous oxide is provided for analgesic purposes, scavenging is not
of Health, March 1996. Further practicable and pollution should be controlled by mechanical ventilation.
guidance is given in ‘Anaesthetic Details of ventilation requirements are given in the appropriate Health
agents: Controlling exposure under Building Notes and Design Guides.
COSHH’, prepared by the Health
Services Advisory Committee, ISBN 0- 3.7 The terminal unit (AGS) is specified in BS 6834: 1992, British Standard
7176-1043-8 for Active Anaesthetic Gas Scavenging Systems. AGSS are covered in
Chapter 10.

3.8 If nitrous oxide is provided in the equipment service room or
workshop, an appropriate AGSS must also be provided.

15


3.9 Medical quality compressed air should be available to at least one
workstation in the equipment service room and workshop. Terminal units in
accordance with BS 5682:1984 (1992) should be provided. The supply should
be taken from the medical air pipeline wherever possible.

3.10 Where an anaesthetic equipment testing area is provided, it will be
necessary to provide medical gases for the testing and calibration of
anaesthetic equipment. A full range of medical gas terminal units will be
required, but wherever possible, medical air should be used for testing
purposes. If medical air is provided instead of the medical gas, the terminal
units must be clearly labelled to prevent confusion: “TEST PANEL – GAS
TERMINAL UNITS CONNECTED TO 4-BAR MEDICAL AIR ONLY”.

3.11 Where gas mixers (blenders) are to be tested, it will be necessary to
provide the appropriate gases. These may be provided either from the MGPS
or from cylinders.

3.12 The specific and special requirements for nitric oxide pipeline systems
are covered separately in Chapter 11.

3.13 Where an array of terminal units is provided at a location, they should
be arranged as follows:

a. for a horizontal array, when viewed from the front, left to right:
oxygen, nitrous oxide, nitrous oxide/oxygen mixture (50% v/v), medical
air 4-bar, surgical air 7-bar, vacuum, anaesthetic gas scavenging, nitric
oxide, oxygen/carbon dioxide mixture:

O2, N2O, N2O/O2, MA-4, SA-7, VAC, AGS, NO, O2/CO2

b. for a vertical array, with oxygen at the top and in the sequence as for a
horizontal array. In many cases a vertical array is impracticable and a
more convenient arrangement will comprise a number of rows, for
example:

O2 N2O and/or N2O/O2

MA-4, SA-7, VAC, AGS, NO, O2/CO2;

c. for a circular array, for example where terminal units are installed on
the undersurface of a pendant, with the sequence as for a horizontal
array, in a clockwise direction when viewed from below. The AGS
terminal unit may occupy the centre of such an array.

3.14 Mounting heights for terminal units should be between 900 mm and
1400 mm above finished floor level (FFL) when installed on walls or similar
vertical surfaces.

3.15 When installed in pendants or similar, terminal units should be of a
type suitable for mounting within the specified fitting.

3.16 Pressure losses across terminal units should be in accordance with
BS 5682:1984. (The standard does not give pressure loss data for surgical air at
350 l/min – but see Table 4.

16


Table 2 Scale of provision of terminal units

Department O2 N2O N2O/O2 MA4 SA7 VAC AGSS

Accident and emergency department
Resuscitation room
per trolley space 1 1 – 1 – 1 1
Major treatment/plaster room
per trolley space 1 1 1p 1 1p 1 1
Post-anaesthesia recovery
per trolley space 1 - – 1p – 1 –
Treatment room/cubicle 1 – – – – 1 –

Operating department
Anaesthesia room 1 1 – 1 – 1 1
Operating theatre
Anaesthetist 1 1 – 1 1p 2 1
Surgeon 1 1 – 1 1p 2 1
per bed space 1 – – 1 – 1 –
Equipment service room
per work space 1 1 – 1 1p 1 1

Maternity department
Delivery suite
Normal delivery room
Mother 1 – 1 – – 1 –
Baby 1 – – 1 – 1 –
Abnormal delivery room
Mother 1 1 1 1 – 2 1
Baby 1 – – 1 – 1 –
Operating suite
Operating theatre
Anaesthetist 1 1 – 1 – 1 1
Obstetrician – – – – – 1 –
Paediatrician
per cot space (*) 1 – – 1 – 1 –
per bed space 1 – – 1 – 1 –
Equipment service room (**)
per work space 1 1 1 1 – 1 1
Neonatal unit
per cot space 2 – – 2 – 2 –
Equipment service room (**)
per work space 1 – – 1 – 1 –
(*) provision for 2 cots only, irrespective of number of cot spaces
(**) Where the Delivery Suite and Neonatal Unit are in close proximity, one equipment service
room can be shared.

In-patient accommodation
Single bedroom 1 – – – – 1 –
Multi bedroom
per bed space 1 – – – – 1 –
Nursery
per cot space (*) 1 – – – – 1 –
(*) provision for 2 cots only, irrespective of number of cot spaces

p = project team option

17


Scale of provision of terminal units


Radiology department
Special procedures room 1 1 – 1 – 1 1
Holding and recovery 1 – – 1p – 1 –
Ultrasound 1 – – – – 1 –
Fluoroscopy 1 – – – – 1 –
Urography 1 – – – – 1 –
General purpose room 1 – – – – 1 –
Tomography 1 – – – – 1 –

In-patient accommodation #
Single bedroom 1 – – 1p – 1 –
Multi-bedroom
per bed space 1 – – 1p – 1 –
Treatment room 1 – – 1p – 1 –
# appropriate for adult acute, children and elderly people

Intensive therapy unit (ITU)
per bed space 2 2p 2p 4 – 4 2p
Equipment service room
per work space 1 1p 1p 1 – 1 1p

Coronary care unit (CCU)

Acute mental illness accommodation
ECT room 1 1 – 1 – 1 1

Adult acute day care accommodation
Treatment room
Anaesthetist 1 1p – 1p – 1 1p
Surgeon – – – – – 1 –

Day patient accommodation
Single bedroom 1 – – – – 1 –
Multi-bedroom
per bed space 1 – – – – 1 –
Treatment room (p) 1 – – 1p – 1 –
Endoscopy room (p) 1 1p – 1p – 1 1p

Fracture clinic
Plaster room 1 1 – 1p 1p 1 1

Oral surgery, orthodontic department
Consulting/treatment room
Type 1 1 1p – 1 – 1 1p
Consulting/treatment room
Type 2 and 3 1 – – 1 – 1 –
Recovery room
per recovery position 1 – – – – 1 –
Appliance laboratory
per workstation – – – – 1 – –


18


Scale of provision of terminal units


Out-patient department
Treatment room 1 1p – 1p – 1 1p

Sterile services department
Washing room – – – 1 – – –
Packing room – – – – 1 – –
Medical equipment re-assembly
per workstation 1 – – 1 – 1 –
Medical equipment workroom
per workstation 1 – – 1 – 1 –


Note:
1. Nitric oxide
Terminal units for nitric oxide may be required as a project team option in intensive therapy units and neonatal units. In
exceptional circumstances, nitric oxide may be required in operating departments. The level of provision would be two
terminal units for each cot or bed space, and two terminal units per theatre.

2. Oxygen/carbon dioxide mixtures
Terminal units for oxygen/carbon dioxide mixtures may be required as a project team option in cardio-thoracic theatres
and in oncology units.

Where, in some ward areas, terminal 3.17 Terminal units which are wall mounted should be located as follows:
units are installed in recesses behind
a. distance between centres of adjacent horizontal terminal units:
covers/decorative panels etc, allow an
additional 100 mm on each side of (i) 35 ± 2.5 mm for three or more terminal units;
the outermost terminal units and 200 (ii) 150 ± 2.5 mm for two terminal units only;
mm from centre to top of recess and
This should be sufficient for double flow meters to be used, for
300 mm from centre to bottom of
example between an oxygen terminal unit and a vacuum terminal unit
recess. The depth of the recess should
serving two bed spaces;
be 150 mm.
b. the distance between the centre of the terminal unit and a potential
obstruction on either side (for example when installed in a corner)
should be a minimum of 200 mm on either side.

19


Terminal units for nitric oxide, oxygen/carbon dioxide mixture

3.18 BS 5682 does not include a terminal unit for nitric oxide or
oxygen/carbon dioxide mixture. In the absence of standards, the dimensions
given in Table 3 are recommended. They are based on the diagrams and tables
in BS 5682:1984 as follows:

Table 3 Recommended probe dimensions for nitric oxide and oxygen/carbon
dioxide mixture (CO2 less than 5%) and NIST dimensions for nitric
oxide

Figure 2 Probe and Table 3 from BS 5682

Diameters of probes

Service Identification Diameter Diameter
symbol C D
Nitric oxide NO 21.48 18.30
21.38 18.20
O2/CO2 O2/CO2 25.00 21.83 mixture (CO2<5%)
(CO2<5%) 24.90 21.73

Figure 5 Body of NIST connector and Table 6 from BS 5682

Diameters of body of NIST connectors

symbol E F
Nitric oxide NO 11.00 +0.11 14.00 +0.11
–0.0 –0.0

Figure 6 Nipple of NIST connector and Table 7 from BS 5682

Diameters of nipples of NIST connectors

symbol H J
Nitric oxide NO 11.00 –0.05 14.00 –0.05
–0.16 –0.16

Nitrogen for surgical tools

3.19 BS 5682 does not include a NIST for nitrogen. In the absence of a
British Standard, the NIST connector allocated in ISO 5359 may be used.

3.20 Where nitrogen is provided for surgical tools, the NIST connector is
recommended with the “body” forming the wall outlet. To avoid the hazard of
discharge of stored energy in low pressure, flexible, connecting assemblies, a
limited leak check valve should be included in the nipple.

20

4.0 Gas flow

General

4.1 A schematic diagram of a typical MGPS is shown in the “Operational
management” volume of this HTM. This diagram shows the pipeline
distribution system from the gas source to the point of use that is the terminal
units.

4.2 There are three aspects of gas flow to consider when designing the
pipeline distribution system:

a. the flow which may be required at each terminal unit;

b. the flow required in each branch of the distribution system (see the
schematic, which shows a system with several main branches);

c. the total flow, i.e. the sum of the flows in each branch.

4.3 The pipeline system should be designed so that the design flows given
in Table 4 can be achieved at each terminal unit.

4.4 If all terminal units were in use simultaneously, excessively large
pipelines and plant would be required. However, since not all terminal units
are used simultaneously, it is necessary to apply a diversity factor to the flow
in each branch of the system, to arrive at a realistic design flow.

4.5 The diversity factors used are derived from the results of surveys of
actual gas usage in typical hospitals.

4.6 The total flow for the system is the sum of the diversified flows to
each department.

4.7 The design engineer should always ensure that due account is taken of
the stated use of a particular department. For example, the number of
terminal units in use for ward areas may be appropriate for a DGH, but the
number may need to be increased for a specialist chest department. The
pipeline is required, however, to meet the peak simultaneous demand and is
designed accordingly. The source of supply will usually be required to deliver a
lower continuous flow.

4.8 It must be remembered that there is a limited range of pipe sizes, and
that where there is any doubt about flow requirements, a larger pipe size
should always be selected.

At the design stage the project team 4.9 All flows are in normal litres per minute (l/min) unless otherwise stated.
should define the individual
room/space required. The definitions
which follow are generic and are not
Gas flow
as detailed as those given in Table 2

Terminal unit flows

4.10 The following formula is used to calculate the volume flow required in
the pipeline at pressure Pg upstream of each terminal unit.

21

4.0 Gas flow

Table 4 Gas flow – flows required at terminal units

Service Location Nominal Flows litres/min
pressure kPa e Design flow Typical flow
required

Oxygen Theatres 400 100 a 20
All other areas 400 10 c 6

Nitrous oxide All areas 400 15 6

Nitrous oxide/ Delivery rooms min 275 20
oxygen mixture All other areas 310 b 20 15
400

Medical air Theatres 400 40 c 40
400 kPa ITU/neonatal 400 80 c 80
CCU 400 80 c 80
Other 400 20 10 c

Surgical air/ Theatres 700 350 d 350
nitrogen

Vacuum Theatres 40 40 40
Recovery (300 40 40
CCU mm Hg) 40 40
Ward areas below 40 40
atmospheric

Nitric oxide ITU, neonatal 400 15 6
theatres

Oxygen/carbon Cardio-thoracic 400 100 40
dioxide mixture theatres, oncology

a. During oxygen flush in operating and anaesthetic rooms.
b. Minimum pressure at 275 l/min.
c. These flows are for certain types of gas-driven ventilators under specific
operating conditions, and nebulisers etc.
d. Surgical tools/tourniquets.
e. Pressure required at terminal unit, not in pipeline.

4.11 The flow Qa required at a terminal unit is expressed in terms of free For manual calculations based on
air flow at standard temperature and pressure (STP). The relationship Table 4, the volume flow is expressed
between volume flow Qa at STP and the volume flow Qg at the pipeline in terms of free air flow Qa and it is,
pressure (Pg) is: therefore, not necessary to calculate
Qg
Qg = Qa*Ap
Pg

where Ap = atmospheric pressure
Pg = pipeline pressure

4.12 The flows required at terminal units, as shown in Table 4, are design
flows for each terminal unit; the actual pipeline distribution design will be
based on the diversified flow rates derived using the methods described in the
following paragraphs.

22

4.0 Gas flow

Pipeline flows

4.13 Normally, because Pg is considered to be constant throughout the
entire pipeline network, the volume flow Qg required in the upstream branch
of a T-junction is simply the sum of the volume flows in the downstream
branches, that is:
n
Qg = ∑ Qa for a = 1...n for n branches
a=1

4.14 By simply adding the downstream flows in this way, the resultant total
flow is higher than that found in practice and would result in unnecessarily
large pipe sizes. Therefore, an allowance for diversity of flow is made.

4.15 As discussed earlier, it is difficult to be predict diversities accurately,
but there are guidelines which can be used and these have been shown to be
adequate in practice.

4.16 For vacuum systems, the minimum vacuum should not fall below
300 mm Hg at each terminal unit at a flow of 40 l/m.

4.17 The design of the pipework system is based on flows and acceptable
pressure loss as shown in Table 4 to include terminal unit pressure loss given
in Table 23, Chapter 15. The overall consumption may be lower in practice,
but the systems would be capable of meeting the calculated demand within
an acceptable range, that is, the design flow operating at a nominal pressure
of 400 kPa.

4.18 Departments usually comprise several ward units and treatment rooms.
In order to avoid confusion, departments should be defined at the project
design stage so that diversified flows may be calculated.

4.19 Pressure requirements for surgical air are based on the requirement
that the minimum pressure should be 700 kPa at this point of use, that is,.
the terminal unit at a flow of 350 l/min.

4.20 Details of pressure requirements for all systems are given in
Appendix K.

Oxygen


4.21 Oxygen is used at a typical flow of 5–6 litres/min. Each terminal unit
should, however, be capable of passing 10 l/min (at STP) at a supply pressure
of 400 kPa (nominal) as shown in Table 4, in case nebulisers or other
respiratory equipment is used.

4.22 The diversified flow to each six-bed room is calculated on the basis
that 10 l/min will be required for the first terminal unit and that only 33% of
the flow to the remainder at 6 l/min will be required. This is equivalent to a
maximum of three terminal units in use simultaneously in a six-bed room.

4.23 In a typical ward comprising four 6-bed rooms, four single-bed rooms
and a treatment room, for the purpose of calculating the diversified flow QW

23

4.0 Gas flow

to the ward, the number of terminal units n used in Table 6 may be taken as
the total number of terminal units in the ward.

4.24 A department may comprise several ward units and treatment suites
where appropriate. The diversified flow for each department, QD, is based on
QW for the first ward unit, plus 50% of the flow for the remaining ward units.
For the purposes of this calculation, the first ward unit can be taken as the
largest ward unit within the department.

4.25 The formula in Table 6 is based on the assumption that a department
comprises a number of identical ward units; where this is not the case, the
diversified flow is QW for the first (or largest ward unit) plus 50% of the total
for the remaining ward units.

4.26 If one ward unit is significantly larger than the others, average the
flows from the ward units to obtain a more realistic flow.

Hyperbaric oxygen chambers

4.27 Monoplace hyperbaric oxygen chambers for clinical purposes should be
supplied from a separate branch. Typical flows for one-person chambers are as
shown in Table 5.

Table 5 Gas flow hyperbaric chambers

Max time for Total consumption Consumption
one complete for max treatment for each additional
treatment time (litres) minute l/min

O2 atmosphere and
recirculation
• on open circuit 2 hours 30,000 250
• on recirculation 2 hours 7250 40

O2 only; no recirculation 2 hours 30,000 250

O2 delivery by built-in 2 hours 1200 10
breathing mask and
overboard pump

O2 delivery by built-in 2 hours 7,200 60
breathing hood and
overboard pump

Note:
1. The flows for a recirculating unit assume the standard method of operation is
recirculation throughout the treatment. It is recommended that the pipeline should be
designed for open circuit operation to ensure adequate flow under all conditions.
2. Clinical practice may require the inclusion of air during the treatment; it may
also be necessary to switch to air in the unlikely event of an oxygen convulsion.
Therefore consideration should be given to the provision of medical air.
3. Some hyperbaric chambers use air as a buffer and considerably less oxygen is
consumed. The advice of the manufacturer should be sought.

24

4.0 Gas flow

Table 6 Oxygen diversified flows

Department Design flow for each Diversified flow
terminal unit l/min Q l/min

In-patient acute
Ward units – single
and multi-bedrooms 10 (n–1)6
QW = 10 +
Treatment rooms 3

Each ward unit
Departments comprising
several ward units
10
{
QD = QW 1+(w–1)
2 }
ITU and CCU 10 QI = 10 + (nB–1)6

Adult acute day care
Major treatment room 100 QT = 100 + 20(T–1)
Endoscopy room 10 QR = 10 + (n–1)6
Recovery room 10 QR = 10 + (n–1)6

Delivery suite 10 QM = 10 + (n–1)6
2

Normal delivery room 100 QM = 100 + (n–1)6
Abnormal delivery room 2

Neonatal unit 10 QN = 10 + (n–1)6

Operating room 100 QT = 100 + 20(T–1)

Anaesthetic room 10 QA = 10 + (A–1)6

Legend for all tables

n = number of terminal units
nB = number of bed spaces
W = number of ward units
T = number of operating rooms or major treatment rooms
A = number of anaesthetic rooms
S = number of operating suites (1 operating room + 1 anaesthetic
room)
Q = diversified flow
QW = diversified flow to ward units
QD = diversified flow to a department
QI = diversified flow to ITU or CCU
QT = diversified flow to operating room or major treatment room
QA = diversified flow to anaesthetic rooms
QR = diversified flow to recovery rooms
QM = diversified flow to maternity suite
QN = diversified flow to neonatal unit
QB = diversified flow to baby bed space
QDent = diversified flow to dental department
QWS = diversified flow to equipment workshop
QP = diversified flow to plaster room

25

4.0 Gas flow

Operating departments

4.28 The diversified flow for operating departments is based on 100 l/min
required for the oxygen flush. Therefore each oxygen terminal unit in the
operating room and anaesthetic room should be able to pass 100 l/min. It is
unlikely that an oxygen flush will be administered simultaneously in several
operating rooms. The diversified flow, QT, is based on 100 l/min for the first
operating room and 20 l/min for the remainder.

4.29 For anaesthetic rooms, each terminal unit should be capable of passing
10 l/min, but the actual flow likely to be used is 6 l/min. The diversified flow is
based on 10 l/min for the first room and 6 l/min for the remainder, since it is
possible that all anaesthetic rooms may be in use simultaneously. Recovery is
considered in a similar way, since again, it is possible that all bed spaces may
be in use simultaneously. To obtain the flow to each operating suite, add the
flows to the operating room and anaesthetic room, that is: 110 l/min.

4.30 The need for an oxygen flush in anaesthetic rooms should be taken into
account in the design. Assume one terminal unit in each department is in use
with oxygen flush at any one time, irrespective of the overall number of
operating suites.

4.31 Major treatment rooms, A & E theatres, surgery and maternity
operating departments should be treated as operating departments.

Intensive therapy and coronary care units

4.32 The diversified flow for these units assumes that all bed spaces may be
occupied. Each terminal should be capable of delivering 10 l/min and the
diversified flow is calculated assuming 10 l/min for the first bed space and
6 l/min for each of the remainder.

4.33 Bed spaces are used instead of numbers of terminal units to calculate
the diversified flow, since each bed space may have up to four (or more)
terminal units associated with it.

4.34 Oxygen should not be used as the driving gas for gas-powered
ventilators if they are capable of being powered by medical air. The minimum
flow characteristic which has proved adequate to drive current types of
ventilator is 80 l/min at 360 kPa.

4.35 If oxygen has to be used to power ventilators and/or ventilators are
operating in continuous positive airway pressure (CPAP) mode, the high flows
which may be encountered should be taken into account both when designing
the pipeline and when sizing the vessel. These ventilators can use exceptional
amounts of oxygen if set up incorrectly.

Maternity

4.36 For all normal delivery suites, the diversified flow is based on
10 l/min for the first terminal unit and 6 l/min for the remainder. In this case,
terminal units are provided for both mother and baby and, therefore, the
number of terminal units rather than rooms should be used to calculate
diversified flow.

26

4.0 Gas flow

4.37 For abnormal delivery suites, provision should be made for the oxygen
flush in the same way as for the operating room. The abnormal delivery suite
should be considered in the same way as the operating department.

4.38 In the event of multiple births, the additional gas usage will have
negligible effect on the total flow.

4.39 The maternity operating suite should be considered in the same way as
operating departments.

Nitrous oxide

4.40 Nitrous oxide is provided mainly for anaesthetic purposes and may be
provided occasionally for analgesic purposes. In all cases each terminal unit
should be capable of passing 15 l/min, but in practice the flow is unlikely to
exceed 6 l/min.

4.41 Therefore, for operating rooms and anaesthetic rooms allow 15 l/min
for the first room and 6 l/min for the remainder.

4.42 It must be assumed that where nitrous oxide terminal units are
provided, they may all be in use simultaneously. Design and diversified flows
for nitrous oxide are given in Table 7.

Table 7 Nitrous oxide diversified flows

Department Design flow for each Diversified flow Q l/min
terminal unit l/min

All departments 15 Q = 15 + (nB–1)6

nB = number of bed spaces or number of rooms as appropriate

Nitrous oxide/oxygen mixture

4.43 All terminal units should be capable of passing 275 l/min for a very
short period to supply inhalationary gasps by the patient, and a continuous
flow of 20 l/min. The actual flow would not normally exceed 20 l/min.

4.44 The diversified flow in intensive therapy units and coronary care units is
based on 20 l/min for the first bed space and 15 l/min for each of the
remainder, since it is possible that nitrous oxide/oxygen mixtures could be
administered at all bed spaces where provided.

4.45 The diversified flow in delivery rooms is based on 275 l/min for the first
bed space and 20 l/min for each of the remainder, of which only 50% will be
in use simultaneously.

4.46 Design and diversified flows for nitrous oxide/oxygen mixtures are
given in Table 8.

27

4.0 Gas flow

Table 8 Nitrous oxide/oxygen mixtures design and diversified flows

Department Design flow for each Diversified flow Q l/min
terminal unit l/min

Delivery rooms 275 QM = 275 + 20(nB–1)
2

Other areas 20 QI = 20 + 15(nB–1)

Medical air

General

4.47 Medical air is used to provide power for several types of equipment BS 4272:Pt 3:1988 provides for
including surgical tools, ventilators and nebulisers. Oxygen should be auxiliary outlets on anaesthetic
avoided as a power source because of fire risk and cost, and should not be machines for both air and oxygen
used where medical air is available, unless specifically recommended by the
device manufacturer.

4.48 Medical air should be provided at two different pressures:

a. a pressure of 400 kPa is required to drive ventilators and for other
respiratory applications;

b. a higher pressure of 700 kPa is required to drive surgical tools. In this
document, medical air at 700 kPa is referred to as surgical air to avoid
confusion.

Medical air 400 kPa

General

4.49 The use of medical air, particularly for respiratory use, has increased
markedly in recent years. This service is the most critical of the medical gas
services, since air-powered ventilators cease to operate in the event of failure
of the supply.

4.50 Medical air is also directly inhaled by patients during ventilation and it
may also be used to dilute oxygen before administration because of the
potentially toxic effects of pure oxygen.

4.51 The supply system for medical air 400 kPa may be a manifold system, a
compressor system or a proportioning system (synthetic air) and includes an
emergency/reserve manifold. A compressor plant should always be specified
where air-powered ventilators are to be used.

4.52 One of the major uses of medical air is for patient ventilators. Patient
ventilators fall into two main categories – those used during anaesthesia and
those used during intensive therapy. Pneumatically powered ventilators can use
up to 80 l/min free air continuously. The exact flow requirements will depend
on the design of the ventilator. The flow and pressure requirements for some
typical ventilators are given in Table 9.

28

4.0 Gas flow

4.53 Current models of anaesthetic ventilators are very similar to intensive
therapy models, and may require peak flows of up to 80 l/min and average
flows of 20 l/min. Almost all such units are pneumatically driven and
electronically controlled.

4.54 Medical air 400 kPa is also used for other equipment such as
anaesthetic gas mixers, humidifiers and nebulisers. The flow rates normally
required would not exceed 10 l/min, and this flow is always in excess of the
actual volume respired.

Pressure requirements

4.55 The minimum pressure required at terminal units for respiratory use is
355 kPa and all terminal units should be tested to ensure that the pressure
does not fall below 355 kPa at flows of: 80 l/min in intensive therapy units
and coronary care units; 40 l/min in special care bay units and operating
suites; 20 l/min in ward areas.

Table 9 Typical pressure and flow requirements for ventilators and nebulisers

Ventilator type Pressure kPa Flow l/min free air

Anaesthesia, typically gas driven, 300–700 1 Pneumatically driven
electronically controlled nominal 400 ventilators use up to
80 l/min
20 l/min continuous

Intensive therapy 300–700 1 180 peak 2
Electronically controlled nominal 400 80 continuous
Gas powered

Neonatal – electronically 300–700 1 80 peak 2
controlled nominal 400 40 continuous
Gas driven

Nebulisers 400 10

Notes:
1. It is strongly recommended that ventilators are not connected to the 700 kPa
system since the blenders only work satisfactorily with a tolerance of about 10% on the
differential pressure for air and oxygen, and incorrect mixtures could be obtained.
2. These flows can be achieved under certain clinical conditions. The peak flows
are usually of very short duration.

4.56 Medical air should not be used to supply mechanical services.

4.57 Some medical gas pendants use the medical air supply for operating
the control/retraction system. This is permitted, provided that:

a. a flow limiting device is provided to protect the medical air system in
the event of failure of any downstream component;

b. a non-return valve is incorporated to protect the system integrity.

4.58 The flow requirements should be ascertained and taken into account
prior to the installation of the equipment.

29

4.0 Gas flow


4.59 In ward areas and treatment rooms, all terminal units should be
capable of passing 20 l/min, although typically 10 l/min will be required.

4.60 The diversified flow to each six-bed room is calculated on the basis of
numbers of terminal units and that only 33% of the flow at 10 l/min will be
required for the remainder. This is approximately equivalent to a maximum of
three terminal units in use simultaneously in a six-bed room.

4.61 In a typical ward comprising four six-bed rooms, four single-bed rooms
and a treatment room, for the purpose of calculating the diversified flow QW
to the ward, the number of terminal units used in Table 10 may be taken as
number of terminal units in the ward.

4.62 A department may comprise several ward units and treatment suites.
The diversified flow for each department, QD, is based on QW for the first
ward unit, plus 50% of the flow for the remaining ward units.

Surgical air 700 kPa

Flow and pressure requirements for 700 kPa surgical air system

4.63 The pressure requirements of surgical tools are between 600 and 700
kPa and flows may vary between 200 and 350 l/min (STP) see Table 11. Most
surgical tools are designed to operate within this pressure range. Higher
pressures are likely to cause damage to tools. Inadequate tool performance,
however, is likely to result from the lack of flow at the specified pressure.

4.64 The introduction of synthetic air (from on-site blending of oxygen and
nitrogen) leads to the possibility of using nitrogen as the power source for
surgical tools. Synthetic air is covered in Chapter 7 “System design – medical
air”.

4.65 The pipeline systems should be designed to provide a flow of 350 l/min
at 700 kPa at the terminal unit. Existing systems may not meet this revised
specification; in any given pipe the pressure drop at a flow of 350 l/min will be
about twice the pressure drop at 250 l/min.

Diversity

4.66 Surgical air 700 kPa is only required where surgical tools are to be
used. This would typically be orthopaedic, neuro-surgery theatres and possibly
plaster rooms. However, to facilitate maximum flexibility, surgical air should be
provided in all theatres. The diversified flow is based on the assumption of
350 l/min for the first theatre and 25% of the remainder – see Table 12.

4.67 Because surgical tools are used only for specific applications, it is
unlikely that more than one tool is actually in use at any given time, even in a
large operating department comprising several theatres.

30

4.0 Gas flow

Table 10 Medical air 400 kPa design and diversified flows


In-patient acute
and multi-bedrooms 20 (n–1)10
QW = 20 +
Treatment rooms 3

Each ward unit
Departments comprising
several ward units
20
{
QD = QW 1+(w–1)
2 }
ITU and CCU 80 QI = nB–1*80
2

Adult acute day care
Major treatment room 40 QT = 40 + (T–1)*40
Endoscopy room 4

Delivery suite 40 QM = 40 + (T–1)*40
4

Normal delivery room 40 QM = 40n
Operating suite 40 QM = 40 + (T–1)*40
4

Neonatal unit 40 QN = 40nB

Dental department
Major dental/oral surgery 40 QDENT = 40nB

Operating room 40 QT = 40 + (T–1)*40
4
Anaesthetic room 40 QA = 40 + (A–1)*40
4
Recovery 40 QR = 40 + (nB–1)*10
4
Plaster room 40 QP = 40 + (nB–1)*40
4

Accident and emergency
Major treatment/ 40 QMT = 40 + (T–1)*40
radiodiagnostic/special 4
procedures

Table 11 Typical pressure and flow requirements for surgical tools

Type of tool Pressure kPa Flow l/min

Small air drill 600–700 200
Medullary reaming machine 600–700 350
Oscillating bone saw 600–700 300
Universal drill 600–700 300
Craniotome 620–750 300

31

4.0 Gas flow

System capacity

4.68 Unlike respirable equipment, surgical tools are used intermittently,
typically for a short burst of a few seconds up to a maximum of 2/3 minutes.
The manifold or plant, therefore, should have the capacity to provide the
design flow of the pipeline for a maximum period of 5 minutes in any
15-minute period.

Table 12 Surgical air 700 kPa design and diversified flows

Department Design flow for Diversified flow Q l/min
each terminal unit
l/min

Operating room 350 QT = 350 + (T–1)350
4

SDU, ODA 350 QWS = 350
workshop etc

Terminal units intended for equipment testing

4.69 It may be necessary to provide surgical air at 700 kPa in the equipment
service workshop for testing purposes. Unless a surgical air 700 kPa pipeline is
available nearby, it may be cost-effective to use portable cylinders, with a two-
stage regulator.

4.70 If a pipeline supply is to be provided, then each terminal unit should be
capable of passing 350 l/min. Where several terminal units are provided, it is
unlikely that more than one terminal unit will be in use at any time, and
therefore the total design flow for the equipment service workshop will be
350 l/min. Because the actual use will be low, it is unlikely that the provision of
such a terminal unit for testing purposes will have a significant effect on the
total design flow for the surgical air 700 kPa system.

Vacuum


4.71 Where vacuum terminal units are provided in ward areas, it is unlikely
that more than one terminal unit in any room (single or multi-bed) will be in
use at any time. Therefore the diversified flow QW should be calculated on the
basis of 40 l/min per ward unit of 28 beds, although each terminal unit should
be capable of passing 40 l/min.

4.72 For a department comprising several ward areas and treatment rooms,
the diversified flow is based on 80 l/min for the first bed and 1 l/min for the
remainder. For treatment rooms, 40 l/min should be allowed for the first room
and it may be assumed that no more than 25% of the remainder will be in use
simultaneously – see Table 13.

4.73 For a hospital comprising several departments, the total flow is based
on 80 l/min for the first bed and 1 l/min for any remaining beds not already
assigned to a specific department.

32

4.0 Gas flow

4.74 A factor of 0.75 should be applied to the calculated total flow to avoid
unrealistically high flows.

Operating departments

4.75 Vacuum is provided for the surgical team and anaesthetist; it is also
provided in the anaesthetic room and recovery.

4.76 Two terminal units are provided in each operating room. Since it is
possible for both terminal units in the operating room to be in use
simultaneously, each operating room will require 80 l/min and each terminal
unit should be capable of passing 40 l/min – see Table 13.

4.77 For anaesthetic rooms, it may be assumed that 40 l/min will be
required at each terminal unit.

4.78 Where there are several operating suites, each comprising one
operating room and one anaesthetic room, the diversity may be calculated on
the basis that for the first two suites no diversity should be allowed, that is,
240 l/min.

4.79 For more than two theatres, it may be assumed that 50% of
remainder will be in use simultaneously at 120 l/min per suite.

4.80 Maternity, accident and emergency theatres, and major treatment
rooms should all be treated as operating rooms.

4.81 Each terminal unit in recovery should be capable of passing
40 l/min. The diversity of flow is calculated on the basis that vacuum is being
used simultaneously at 25% of bed spaces (minimum one).

Table 13 Vacuum design and diversified flow


In-patient acute
and multi-bedrooms 40 QW = 40
Treatment rooms 40 OT = 40 + (nB–1)*40
4

Departments – ward areas 40 QD = 80 + (nB–1)*1

Operating room 40 QT = 80
Anaesthetic room 40 QA = 40
Operating suite
1 operating room 40 QS = (120*2) + (S–2)*120
2
Recovery room 40 QR = 40 + (nB–1)*40
4
ITU and CCU 40 QI = 40 + (nB–1)*40
4

33

4.0 Gas flow

Intensive therapy unit, coronary care unit and neonatal unit

4.82 Each terminal unit should be capable of passing 40 l/min, but it may be
assumed that only 25% of bed spaces will require vacuum simultaneously
(minimum one).

4.83 All other high-dependency areas should be treated as ITU/CCU.

34

5.0 System design – general

Cylinder manifold installation

General

5.1 Manifolds should be connected to the pipeline via a control panel
which provides two equal banks of gas cylinders. The changeover from the
“duty” to the “standby” bank of cylinders should be automatic. All manifolds
should be capable of passing the full pipeline flow. The temperature of the
gas may fall as low as –30°C as the gas passes through the regulator at
maximum capacity, and the equipment should be designed accordingly.

5.2 A schematic layout for a typical installation is given in Figure 1. Total
storage is usually provided on the basis of one week’s supply; each bank of
the manifold should hold not less than two days’ supply and a supply for
three days should be held in cylinders in the store.

5.3 The nominal and usable capacity of the cylinders commonly used on
manifolds are given in Table 14 (the figures are the equivalents at standard
temperature and pressure).

Table 14 Capacities of medical gas cylinders used on manifolds

Gas Nominal capacity (litres) **Usable capacity
at 137 bar g (litres)

Oxygen J size 6,800 6,540
Nitrous oxide J size 18,000
G size 9,000 8,900
Nitrous oxide/oxygen 5,000 4,740
mixtures G size
Medical air J size 6,400 6,220
5,550

Oxygen/carbon dioxide 6,800 6,540
mixture (5% CO2) J size

Nitric oxide AU size 1,500* –
Nitric oxide AK size 4,000* –

* This may be subject to change.
** The usable figures are for discharges down to a gauge pressure of
7 bar g. Two sets of figures are provided for air – for 400 kPa systems
and 700 kPa systems – the latter is for discharge down to 15 bar g.

5.4 An automatic manifold changeover from “duty” to standby should
occur at a cylinder pressure which will ensure the greatest possible utilisation
of the contents of the cylinders in the “duty” bank. If the normal operation of
the changeover control depends on an electricity supply, the design should be
such that failure of the electricity supply does not disrupt the flow of gas to
the distribution system.

35


Figure 1 Schematic layout of cylinder manifold (400 kPa) system (reproduced by kind permission of MEDÆS)

36


5.5 Manifolds and control panels should be designed and certificated for
use with 230 bar g cylinders. The manifold headers should incorporate a
renewable non-return valve to allow removal and replacement of any cylinder
and to prevent the discharge of a bank of cylinders in the event of “tail-pipe”
rupture. The “tail-pipe” manifold connector should be gas-specific.

Some manifolds default to a specific 5.6 In the event of power failure, on restoration of the power supply, the
bank following a power failure, original running bank should be on-line, that is, the same bank as was the
regardless of which bank was the running bank prior to interruption of the supply.
running bank prior to interruption of
the supply. 5.7 The tail-pipe cylinder connector must be a pin-index yoke connector in
accordance with BS 1319 for oxygen, nitrous oxide/oxygen mixture (50% v/v)
and medical air. The connector for nitrous oxide should be a side outlet valve
connector in accordance with BS 341 PE1. The manifold connectors should be
in accordance with the following:

M26 x 2 O2/CO2
M24 x 2 Air
M22 x 2 N2O/O2
M20 x 2 O2
M18 x 2 N2O
M16 x 2 NO
M14 x 2 N2 oxygen free (purge)

5.8 Pressure indication should be provided to indicate pressure in each
cylinder bank and in the MGPS.

Pressure control

5.9 The pressure control should maintain the nominal pipeline pressure
within the limits given in Appendix K.

5.10 There should be separate pressure regulating valves for each cylinder
bank and the control system should be designed so that the cylinders of one
bank can be changed, or the pressure regulator for one bank can be
overhauled, without loss of continuity of the gas supply.

5.11 Pressure safety valves should be of the self-closing type and be
installed on each distribution pipeline downstream of the manifold line
pressure regulator and the main isolation valve. A pressure safety valve should
also be installed between the emergency/reserve manifold and the pipeline
distribution system. It should have a flow capacity at least equal to that of the
pressure regulator immediately upstream of it. The discharge pipe should be
at least one size larger than the main pipeline.

5.12 This discharge pipe line should be vented to atmosphere, outside the
building, in an area where the discharge of oxygen, nitrous oxide, nitrous
oxide/oxygen mixture, oxygen/carbon dioxide mixture, and nitric oxide or
nitrogen will not contribute to a fire risk, or cause injury to personnel.

5.13 It should be well clear of any openable window or air intake. The ends
of the discharge pipelines should be turned downwards to prevent the ingress
of dirt and moisture, and be placed and protected so that frost cannot form
or be collected upon them. Similar safety valve arrangements are required for
installations supplied from liquid oxygen cylinder installations.

37


Manifold monitoring and indicating system

5.14 The monitoring and indicating system should perform the following
functions:

a. overall manifold monitoring;

b. manifold condition indication;

c. overall supply plant indication.

All functions should be appropriately identified. Indicators should have a
design life of at least one year. The system should be capable of automatic
reinstatement after restoration of the power supply.

5.15 Manifold monitoring, indicating and alarm systems should be on the
essential electrical supply.

Manifold control unit

5.16 The control unit should include a green “mains supply on” indicator.

Manifold monitoring

5.17 Each automatic manifold should be provided with monitoring to
detect:

a. duty bank operating;

b. duty bank empty and standby bank operating;

c. standby bank below 10% capacity when the duty bank is empty;

d. reserve bank below nominal 14 bar g (for nitrous oxide) and below The emergency/reserve manifold is
68 bar g pressure for other gases; monitored for condition (d)

e. pipeline pressure faults below –20% or above +20% of nominal
pressure.

Manifold indicator unit

5.18 There should be indicators to show the following conditions:

a. for each automatic manifold:
(i) a green “running” indicator for each bank. This should display
when the bank is supplying gas, irrespective of the pressure;
(ii) a yellow “empty” indicator for each bank when the running In practice, conditions (ii) and (iii) are
bank is empty and changeover has occurred; the same
(iii) a yellow “low pressure” indicator for each bank to be
illuminated after changeover, when the pressure in the bank
now running falls to the low pressure setting;

b. for each emergency/reserve bank a yellow indicator to be illuminated
when the pressure in the bank falls below 14 bar g for nitrous oxide or
below 68 bar g for other gases;

c. for the pipeline distribution system a red “low pressure” and a red
“high pressure” indicator to be illuminated when the respective
conditions occur.

38


Alarm signal status unit

5.19 The following indication of manifold conditions should be provided:

Indication Legend

a. green “normal” normal

b. yellow “duty bank empty,
standby running” change cylinders

c. yellow “duty bank empty,
standby low” change cylinders immediately

d. yellow “emergency/reserve
banks low” reserve low

e. red “pipeline pressure fault” pressure fault

5.20 Conditions (b) to (e) should be transmitted to the central alarm system.
Where relays are used, they should be normally energised relays which
de-energise under fault conditions, with contacts having a minimum rating of
50V dc, 50 mA.

5.21 Alternatively, volt-free, normally closed contacts rated at 50 V dc, 50
mA should be provided for transmission of conditions (b) to (e) to the alarm
system.

5.22 The panel can be incorporated into the manifold control unit or be a
separate unit within the plantroom. If mounted separately, the cabling should
be monitored for open/short circuit. In the event of such a cable fault, a red
“system fault” lamp should be illuminated on the alarm signal status unit,
together with the appropriate alarm condition.

Emergency reserve supply

General

5.23 A permanently connected reserve supply system must be provided for
all MGPS including nitric oxide systems (excluding 700 kPa surgical air
systems), for emergency use or to permit servicing or repair.

5.24 The reserve supply should be designed, when practicable, to provide
the same flow rate as the primary system and have sufficient connected
capacity to supply the pipeline for at least 4 hours. When such provision
would result in six cylinders or more on each bank, the additional cylinders
should be held in the manifold rooms. A non-return valve and isolating valve
should be installed immediately upstream of the reserve manifold connection
to the pipeline distribution system.

5.25 The requirements for the emergency/reserve supply capacity should be
set out in the operational policy and should take into account the local supply
situation for cylinders, liquid supply in the event of an emergency and the
system flow that would be required. The gas supplier should be consulted.

5.26 The specific requirements will depend on the method of primary
supply. Where this results in an unrealistic number of cylinders being kept on
site, the operational policy should be set out giving details of procedures to be
followed in an emergency, to ensure continuity of supply.

39


5.27 For large installations, it may be impractical to rely on a cylinder
manifold system and consideration should be given to either a bulk liquid or
liquid cylinder emergency/reserve supply.

5.28 The operational policy should set out the action to be taken in the
event of loss of the primary source of supply.

5.29 In the event of loss or failure of the primary source of supply, the
emergency/reserve system should be able to provide (at least for a short time)
the total system flow, since it will not always be possible to advise users
immediately of an emergency situation.

5.30 The operational policy should provide details of further action to be
taken, location of emergency manifolds, cylinders etc.

Emergency reserve supplies for manifold installations

5.31 The supply should be brought into operation automatically via a non-
return valve.

5.32 A two-cylinder emergency reserve supply would normally be considered
adequate for a cylinder manifold supply system. The cylinder valve of one
should be permanently open so that gas is immediately available. The cylinder
valve of the second cylinder should be closed so that by alternative use a
continuous supply can be maintained. A typical system is shown in Figure 2.

Emergency reserve supply for air compressors/liquid oxygen/oxygen
concentrators (PSA)

5.33 The supply should normally comprise a two-bank manifold system.
A typical number of cylinders in each bank would be five or six depending on
size and location. See also the Chapter on bulk liquid oxygen supply systems
for more details of the back-up and emergency supply facility.

Location

5.34 The emergency/reserve manifold for the cylinder system should be
located in the manifold rooms of the primary supply. Reserve manifold rooms
for other systems should similarly be installed in an appropriate manifold room.

Design

5.35 Except as stated herein, emergency/reserve manifold systems should
conform to the requirement for manifold supply systems in general.

5.36 The emergency/reserve supply to the cylinder manifold should come
into operation automatically, in accordance with the requirements for manifold
supply systems for 400 kPa systems given in Chapter 5.

5.37 Provision should also be made for an emergency/reserve inlet supply for
either a replacement or alternative supply.

5.38 Emergency/reserve supplies for liquid oxygen systems are covered in the
“Bulk liquid oxygen systems” section of Chapter 6. It may be advisable to
locate the emergency/reserve supply, or the emergency supply facility, where
provided, in a location remote from the primary source of supply.

40


Figure 2 Emergency supply manifiold (reproduced by kind permission of MEDÆS)

41

6.0 System design – oxygen supplies

Bulk liquid oxygen systems and vacuum insulated evaporator (VIE)

General

6.1 A VIE can be used for the storage of any cryogenic liquid which can
include, in healthcare premises, oxygen, nitrogen and nitrous oxide. The VIE is
a cryogenic pressure vessel made of stainless steel supported within an outer
vessel, similar to a vacuum flask. The VIE plant has advantages over other
oxygen supply systems where high demands exist, and is used whenever it can
be shown to be more economical, provided that a suitable location is available.
Bulk liquid oxygen installations show significant manual handling savings over
conventional cylinder manifolds. This part of the system usually remains the
property and responsibility of the gas supplier, who retains full legal
responsibility for compliance with the maintenance requirements and the
Pressure Systems and Transportable Gas Containers Regulations 1989.

6.2 The hospital should be made aware of the general operating principles
by the medical gases contractors and will need to include the VIE system in the
hospital alarm system.

6.3 Consideration should be given to the legal and operational
management consequences of using a different supplier of oxygen on the
same pipeline system. Any contracts involving different suppliers should clearly
state the obligations and limitations of liabilities.

6.4 The consumption of oxygen is increasing steadily, and in order to
ensure continuity of supply it is essential that the VIE is correctly sized for the
demand, and that a telemetry system is installed.

System sizing

6.5 The liquid oxygen vessel is normally selected to provide for at least
14 days’ consumption. An emergency back-up supply equivalent to 24 hours’
average use should be available on site. This may be provided by bulk liquid,
liquid cylinders or compressed gas cylinders, as appropriate for each site.

6.6 A maximum of 20 cylinders are normally connected to the emergency
manifold – ten on each bank. Where it would be impractical to hold 24 hours’
supply in cylinders on site (for example, in a large teaching hospital),
consideration should be given to the ease of supply in an emergency, for
example proximity to gas supplies depots, telemetry systems, etc, to see
whether it would be possible to reduce the number of cylinders on site. It is
essential that any relaxation of the number of cylinders held should be
validated and documented with the gas supplier, clearly stating responsibilities
and expectations for supply of cylinders.

6.7 Where additional outlet points are installed on a pipeline system fed
from a VIE, the hospital should notify the gas supplier to ensure that changes
in consumption do not jeopardise the security of stock.

42


6.8 With the use of telemetry systems, it is possible to monitor gas usage
and thus optimise the delivery frequency whilst maintaining adequate stocks.
The gas supplier should advise on the most appropriate vessel size for a
particular site, geographic location, and the standby requirements, taking into
account the demand, peak consumption and site location.

Equipment description

6.9 The system is designed to provide:

a. a liquid oxygen VIE at a pressure of at least 10.5 bar g;

b. standby oxygen facility with a capacity of at least 24 hours’ usable
supply to protect against VIE supply failure;

c. stand-alone emergency supply facility, where appropriate, to protect
against failure from the VIE to the hospital.

Standby oxygen facility

6.10 This may be provided by:

a. standby liquid oxygen VIE;

b. manifold liquid cylinders;

c. manifold compressed gas cylinders.

System layout

6.11 The various systems are:

Figure 3 VIE with cylinder back-up;

Figure 4 VIE with VIE standby;

Figure 5 VIE with liquid cylinder standby.

VIE

6.12 A VIE installation comprises:

a. a vacuum insulated tank to store the bulk liquid at the appropriate
operating pressure;

b. a pressure raising system to maintain the VIE operating pressure;

c. a vaporiser system to convert the liquid into gaseous product at
ambient temperature.

6.13 The control panel and instrumentation for the VIE are normally
mounted centrally at the front of the vessel. Pressure vessel details are given
on a plate mounted on the outer vessel. The vessel must be clearly labelled
with the product name.

6.14 A separate ambient vaporiser system converts the liquid into gas at the
required working pressure of 10.5 bar g.

43


Figure 3 Typical VIE layout and pipework configuration with cylinder backup (reproduced by kind permission of BOC)

44


Figure 4 Typical VIE layout and pipework configuration with VIE standby (reproduced by kind permission of BOC)

45


Figure 5 Typical VIE layout and pipework configuration with liquid cylinder standby (reproduced by kind permission of
BOC)

46


Control piping and instrumentation

6.15 The VIE pipework configuration will depend on the standby system.
The VIEs have top and bottom fill connections with a liquid outlet supply to
the vaporiser and a top gas economiser connection.

The valve information applies to BOC 6.16 IT IS NOT RECOMMENDED THAT ANY OF THE VALVES ARE
VIEs only. If other manufacturers’ OPENED OR CLOSED EXCEPT BY THE GAS SUPPLIER’S PERSONNEL OR
installations are in use, the operating EXCEPT IN AN EMERGENCY BY AUTHORISED PERSONNEL.
procedures should be ascertained by
the authorised person (MGPS) for the
Pressure raising system
site.
6.17 The pressure of the VIE is automatically controlled by a pressure raising
regulator which controls the flow of liquid to the pressure raising vaporiser as
required. The vaporised liquid maintains the VIE gas space pressure at a
minimum of 10.5 bar g.

6.18 Where several vaporisers are installed, there should be automatic
control of changeover to prevent excessive icing of an individual vaporiser.

Direct reading contents gauge and telemetry systems

6.19 The contents gauge of the VIE is of the differential pressure type,
indicating the liquid content. Calibration curves required for use with
differential pressure gauges should be provided by the gas supplier.

6.20 A telemetry system should be installed which continuously monitors
and records the tank contents and tank pressure. This information can be
used to identify liquid levels and consumption rates, and can indicate the VIE
operating condition to assist maintenance requirements.

6.21 This data will be transmitted to both the hospital and the gas supplier
as required.

6.22 Telemetry systems data can be used to predict the consumption rates
and future demands.

6.23 Safety note – VIEs are strictly designed and manufactured to
recognised national/international codes. Associated equipment is designed to
the appropriate standards and authorised by design authorities.

6.24 There must be no modification to the design of any part of the VIE
system without written authorisation from the gas supplier.

6.25 Records should be kept of design, installation, maintenance and of any
modifications which are carried out by the hospital and the gas supplier.

Control panel

6.26 The VIE medical control panel is designed to accept a supply of
gaseous oxygen from the VIE (at 10.5 bar g) or from the standby manifold (at
8.5 bar g) and to reduce the pressure to 4.2 bar g in the oxygen pipeline
distribution system.

47


Sites for liquid oxygen storage

6.27 The VIE should be located inside a fenced compound, which may also
house the control panel and the standby manifold. The location should be
acceptable to both the gas supplier and the hospital, and should be exclusively
reserved for the storage of liquid oxygen and other non-flammable cryogenic
liquids. The vessel should not be located inside a building. It may be necessary
to comply with local authority planning constraints in some areas. The site
chosen should comply with the safety distances in the British Compressed
Gases Association Code of Practice 19 – ‘Bulk Liquid Oxygen Storage at Users’
Premises’.

6.28 Space should be provided to facilitate any manoeuvring of the delivery
vehicle. Typical turning circle dimensions are as follows:

Coupled length m Width m Turning circle m

Articulated vehicle 16.5 2.5 27.5

Rigid vehicle 8.6 2.5 20.0

6.29 The safety distances shown in Figures 6 and 7 are taken from the
BCGA Code of Practice. The vessel should be at least 8 m from roads, drains,
buildings etc. The plinth should be concrete and should have free access at all
times and be designated a “no parking” area. It should be free from rubbish,
empty cylinders, and not used as a general storage area. The VIE compound is
not a cylinder store. It is also important that it is served by a good road, wide
enough and with turning facilities for road tankers. The road must be kept
unobstructed at all times.

Operation

6.30 During normal operation of the system, the valves should be in the
positions indicated below:

Valve ref/description Normal operation To reduce normal pressure

Gas withdrawal Closed Open

Liquid withdrawal Open Closed

Gas isolating Open Open

Liquid isolating Open Closed

Top fill Closed Closed

Bottom fill Closed Closed

6.31 Oxygen is supplied to the control panel at a pressure of 10.5 bar g
where its pressure is reduced to 4.2 bar g before it flows to the pipeline
distribution system. The control panel comes supplied with the following alarm
conditions:

Standby system in use

6.32 Should the oxygen supply from the main VIE fail, the standby system
will automatically supply oxygen and simultaneously a “standby in use” alarm
will be given.

48


Figure 6 Safety distances for cryogenic storage vessels (reproduced by kind permission of BOC and BCGA)

49


Figure 7 Safety distances for cryogenic storage vessels (reproduced by kind permission of BOC and BCGA)

50


51


6.33 Safety note: this is not the initial alarm condition of the system.
The VIE (see user manual) is supplied with a differential pressure switch
for liquid level alarm. The VIE user manual should describe in detail the
operation and actions necessary should this alarm condition be
initiated.

6.34 The VIE level alarm and “standby in use” alarm will remain on until the
VIE is refilled.

Standby low

6.35 Should no action be taken after VIE supply failure the standby system
will supply until pressure falls to a pre-set pressure at which time a “standby
low” alarm will be given.

Low line pressure

6.36 Gas usage without VIE or cylinder replenishment will cause further
pressure drop. At an outlet pressure of 3.75 bar g, a “low line pressure”
alarm will be given. This alarm condition will also be initiated in the event of a
regulator within the control panel failing shut or a pipeline failure.

High line pressure

6.37 If a regulator within the control panel fails open, a high pressure alarm
“high line pressure” will be given at 4.9 bar g.

6.38 Emergency shutdown:

a. in case of vessel safety valve blowing:
(i) close valve (liquid supply to vaporiser) to reduce VIE pressure to
below 16 bar g;
(ii) notify the gas supplier immediately;

b. in case of vessel bursting disc blowing:
(i) close valve (liquid supply to vaporiser) to reduce VIE pressure;
(ii) check that VIE pressure is below 16.0 bar g;
(iii) change valve to alternative bursting disc position;
(iv) notify the gas supplier immediately.

VIE filling

6.39 After commissioning, subsequent filling of the VIE is controlled by the All users should check their own
gas supplier. The driver should fill the VIE without disturbing the customer’s installations and ensure that they are
supply pressure or flow and without lifting safety valves or blowing bursting aware of the operating instructions.
discs. After filling, the driver should report any defects to the gas supplier The advice of the gas supplier should
immediately. also be sought in cases of doubt.

Maintenance

6.40 Maintenance is the responsibility of the gas supplier, but there are
customer checks which should be carried out daily and weekly. In addition, it
will be necessary to test the alarm system.

52


The high line pressure alarm requires 6.41 To test the alarm system, each alarm condition is initiated by the
specialist test equipment and the gas operation of a pressure switch. The control panel is supplied with three-way
supplier should normally be contacted ball valves on the oxygen supply lines to each pressure switch. Rotation of
to carry out this test. these valve handles through 180º allows oxygen pressure to the pressure
switches to be reduced, which operates the pressure switches and the
appropriate alarms.

Standby oxygen facility

6.42 A standby oxygen facility must always be provided.

6.43 It should be sized to provided 24 hours’ capacity, at average
consumption, by bulk liquid, liquid cylinders or compressed gas cylinders.

6.44 In the event of failure of the main VIE, the standby system should
come into operation automatically. There should be a non-return valve to
protect the standby system venting through the VIE in the event of a fault.

Back-up bulk liquid storage vessel

6.45 This should be sized to provide 24 hours’ supply at 50% capacity.

6.46 To prevent unnecessary gas losses, the economiser circuit should be
piped into the main supply distribution system downstream of the main
vaporiser.

6.47 The back-up vaporiser should be sized to provide 24 hours’ usage at
average flow rates.

Liquid cylinder back-up

6.48 The number of liquid cylinders required will depend on the flow rate
requirements, rather than the capacity.

6.49 To prevent unnecessary gas losses, the economiser circuit should be
piped into the main supply downstream of the main supply vaporiser.

Compressed gas cylinder back-up

6.50 The minimum size of the back-up manifold should be a 2 x 5 (J-size
cylinders).

6.51 There should be sufficient additional cylinders on site to provide
adequate back-up, and arrangements should be made to ensure that
24 hours’ supply is available.

Emergency supply facility

6.52 Where a risk assessment has identified a potentially vulnerable
situation, such as a remote liquid facility separated from the hospital by
roadways etc, then it may be advisable to consider an additional emergency
supply facility.

53


6.53 This may be either:

a. a permanent manifold system, located within the main hospital
complex;

b. a portable manifold system (for example 2 x 1 J-size cylinders) mounted
on a trolley for immediate use, to be connected via non-
interchangeable screw thread (NIST) connectors for use in specific
departments.

6.54 Where such a permanent manifold is installed, this may fulfil the
standby requirements if appropriately sized.

6.55 For a permanent manifold, it should be fully automatic and protected
by non-return valves and suitable valving arrangements (as indicated in the
“Cylinder manifold installation” section of Chapter 5).

6.56 All cylinders, whether on VIE back-up or manifolds, should be routinely
inspected and be subject to stock control procedures. Specific attention should
be given to expiry dates on the batch label fitted to each cylinder.

6.57 All gas manifolds should be subject to routine maintenance.



Indication Legend


b. yellow “VIE low < 25%” re-fill liquid

c. yellow “VIE empty, standby re-fill liquid
in use” immediately

d. red “pressure in standby reserve low
system <50%”

e. red “pipeline pressure fault
pressure fault”

50 V dc, 50 mA.

mA should be provided for transmission of conditions (b) to (e) to the alarm
system.

6.61 The panel can be incorporated into the VIE control unit within the VIE
compound, or be a separate unit within the enclosure. If mounted separately,
the cabling should be monitored for open/short circuit. In the event of such a
cabling fault, a red “system fault” lamp should be illuminated on the alarm
signal status unit, together with the appropriate alarm condition.

54


Liquid oxygen supplies

General

6.62 Traditionally, piped medical oxygen has been supplied from
compressed gas cylinder manifolds or VIEs, depending upon the oxygen usage
rate and storage requirements. The introduction of a supply by liquid cylinders
provides greater flexibility of storage facility for mid-range gas volumes
between the smaller compressed gas manifold capacities and the more
substantial bulk liquid volumes.

6.63 The advantages of medical oxygen liquid cylinders are:

a. increased handling efficiency;

b. labour saving for the hospital;

c. improved safety environment;

d. greater security of supply and stock holding;

e. reduced manifold and cylinder space.

6.64 A typical installation is shown in Figure 8. Due to increasing oxygen
consumption, the use of telemetry systems to monitor cylinder contents is
recommended. (See also telemetry systems for VIE systems in the “Bulk liquid
oxygen” section of Chapter 6.)

Liquid cylinder design

6.65 Medical oxygen liquid cylinders are double-walled with vacuum and
multi-layer insulation. They are suitable for transportation and storage of
liquid oxygen, and provide a complete self-contained gas supply system for
hospital use.

6.66 Cylinders are designed and supplied with gas-specific liquid fill and gas
use connections, as follows:

a. Liquid fill – CGA 440;

b. Gas use – ISO 5145.

Liquid cylinder manifolds

6.67 In practice, to cater for normal supply requirements, liquid cylinders
will be required to be manifolded together with the attendant control panel,
alarm and standby supply systems.

6.68 The manifold is designed to allow a number of liquid cylinders to be
manifolded together in such a way as to complement their particular
operating characteristics, giving a single gas outlet point to the control panel.

Control panel

6.69 The control panel is designed to maintain an outlet pressure of 4.2 bar
g at a required flow rate of up to 30 Nm3/hr (500 l/min).

55


Figure 8 Typical liquid cylinder installation (reproduced by kind permission of BOC)

56


6.70 The standby supply feeds into the control panel and, in the event
of the liquid cylinder pressure dropping below a pre-set value, a flow of
oxygen will commence automatically. This ensures that a constant supply of
oxygen at the correct pressure is maintained.

Emergency compressed oxygen manifold

6.71 The emergency oxygen supply consists of a manual or automatic
changeover manifold which comes into operation automatically. The manifold
size, and quantity of hospital stock, should be dictated by a particular
hospital’s requirements.

Siting requirements

6.72 It is not recommended that liquid cylinders are installed within
buildings; they should be installed in the open air in an enclosure designed for
the purpose.

6.73 Cylinder sites should be well-ventilated areas, away from any heat
source.

6.74 Where there is no alternative, a liquid cylinder manifold may be
installed in a building or a confined area, but only if the vent header (to which
all liquid cylinder vents will be connected) is piped to a safe area via a back
pressure control valve. This valve should be set at a pressure below that of the
liquid cylinder relief valve setting, thus ensuring any excess pressure is vented
to a safe area in a safe manner.

6.75 Where installed in buildings, generous ventilation should be provided
by means of fully-louvred access doors to the outside.

6.76 The appropriate calculation must be made to ensure that there is
adequate ventilation.

6.77 The site should be free from obstructions, with sufficient access to the
liquid cylinders, manifold, control panel and fill point.

6.78 The floor on which the liquid cylinders will be located (and where they
will be filled) should be concrete hard-standing, strong enough to support the
weight of the cylinders when full.

6.79 The floor should be level but designed to avoid any accumulation of
water in the vicinity of the liquid cylinders.

6.80 The cylinders should be located at least 3 metres from:

a. open sewers/drains;

b. pits;

c. trenches;

d. any openings to underground rooms/enclosures;

e. any combustible materials.

6.81 For further guidance on liquid cylinder location, refer to EN 1251
‘Cryogenic vessels – transportable vacuum insulated of not more than 1000
litre volume – operational requirements’ and the BOC Guidance Notes, Form
G4521.

57


Liquid cylinder manifold sizing

6.82 The manifold will be sized according to the average annual usage, with
liquid cylinder installations being ideally suited to annual consumptions of
between 3000 and 40,000 Nm3 per annum.

6.83 As the lower end of the medical VIE range reflects a minimum annual One 200 litre liquid cylinder (LC 200)
usage of approximately 27,500 Nm3 per annum, there is an overlap of would have a capacity equal to
annual consumption between 27,500 Nm3 and 40,000 Nm3 per annum, approximately 24 J-sized cylinders
where either a bulk VIE or a liquid cylinder installation could be considered
to satisfy a particular requirement or accommodate possible site restrictions.

Refilling

6.84 Refilling of liquid cylinders is carried out in situ, including pre- and post-
analysis and certification of the cylinders. The cylinder manifold is equipped
with a fill header which enables “remote” filling of multiple cylinders in situ.


6.85 The alarm signal status unit is the same as for VIE systems.


Indication Legend

a. green “normal” indicator normal

b. yellow “liquid low < 25%” re-fill liquid

c. yellow “liquid cylinders re-fill liquid
empty, standby in use” immediately

d. red “pressure in standby reserve low
system < 50%”


Conditions (b) to (e) should be transmitted to the central alarm system. Where
relays are used, they should be normally energised relays which de-energise
under fault conditions, with contacts having a minimum rating of 50 V dc,
50 mA.

mA should be provided for transmission of conditions (a) to (e) to the alarm
system.

6.88 The panel can be incorporated into the liquid cylinder manifold control
unit, or be a separate unit within the accommodation. If mounted separately,
the cabling should be monitored for open/short circuit. In the event of such a
cabling fault, a red “system fault” lamp should be illuminated on the alarm
signal status unit, together with the appropriate alarm condition.

58


Oxygen concentrator installations (PSA plant)

General

6.89 Oxygen concentrators or pressure swing adsorber (PSA) systems may
be an alternative to the more traditional supply systems (the terms oxygen
concentrator and PSA are interchangeable). Typical installations where PSA
systems should be considered are those sites having no access to reliable
liquid supplies, such as remote or off-shore sites or where the safety criteria
for a bulk liquid vessel cannot be met (for example, very restricted sites).
Otherwise, PSA systems should only be installed when an investment appraisal
shows them to be economical.

6.90 When installed, a PSA system will deliver product gas via the “oxygen”
pipeline system.

6.91 Oxygen concentrators operate by adsorbing, under pressure, other
gases in the atmosphere onto materials which have specific physio-chemical
properties, thus freeing the oxygen which is stored and transmitting it for use.
The adsorbents are known as artificial zeolites and are more commonly
referred to as molecular sieves. The sieves are arranged in pairs, one adsorbing
whilst the other regenerates. The waste product, essentially nitrogen, is
discharged to atmosphere during regeneration of the adsorbents. In some
systems, the use of vacuum increases the efficiency of the regeneration/
adsorption process. Regeneration requires the use of a small proportion of the
product gas.

6.92 The PSA process has reached a high level of technical sophistication
and is capable of producing oxygen with a concentration of about 95%. (For
the UK the minimum level, below which the emergency/reserve manifold will
come into operation, is 94%.) The remainder is mainly argon with some
nitrogen. The highest concentration is not likely to exceed 97/98%, except
when the emergency/reserve manifold is in use, when it will be 100%.

6.93 The major components of a PSA system and their layout are shown in
Figure 9. The typical major components of the system are the compressors,
receiver, dryers, molecular sieves, vacuum pumps, filters and regulators. Other
components are identical to those used for medical air and vacuum plant,
which are described fully in the appropriate sections. A suitable operating and
indicating system is also required, as specified below. Package supply systems,
which should be specified to meet the requirements given in this
memorandum, are available from manufacturers.

Siting

6.94 The plant should have all-round access for maintenance purposes and
allowance should be made for changing major components.

6.95 The siting of the plant should allow for adequate flows of air for three
different purposes:

a. air intake to the compressors;

b. cooling of the compressed air by the after-coolers;

c. cooling of the compressors.

59


Figure 9 Schematic diagram of a typical PSA installation

60


6.96 Each compressor may require ducting to ensure an adequate flow of
cool air. The manufacturer should be consulted over the range of operating
temperature for which the system is designed. In extreme circumstances,
refrigeration of the cooling air may need to be provided.

6.97 Air inlet filters should be fitted either to the compressor inlet or at a
suitable point in any ductwork. The filters should comply with BS 7226:1989
and be either dry medium filters or grade CA paper element filters.

Plant configuration

6.98 The plant should comprise:

a. duplex compressor – if more than two compressors are installed, the
plant should provide the design flow with one compressor out of
service;

b. duplexed air treatment/molecular sieve devices, that is, two sets of
filters and a pair of molecular sieves (one adsorbing whilst the other
regenerates), and one vacuum pump (if required by the manufacturer).

6.99 All duplexed components should be capable of independent operation.

Compressors and vacuum pumps

6.100 The compressors for the PSA systems may be any of the type
recommended for compressed air systems. It is also possible to provide a
combined medical air PSA plant. Generally, the compressed air requirement
per litre of product gas is of the order 4:1, and as a result the compressor
plant will be on longer than that typically seen in hospitals.

6.101 A vacuum pump may be required as part of the system. The vacuum
pump, if provided, is utilised during the adsorption/regeneration process.
Vacuum pumps may be of any type as for the piped medical vacuum system.
It will not generally be practicable to use water sealed pumps nor to utilise the
medical vacuum plant.

Compressor noise

6.102 The noise level produced by the compressors will increase with the
capacity of the supply system. The maximum free field noise level for
unsilenced compressed air plant, at 1 m from the plant, varies with the type
and power of the plant but should not normally exceed the following values:

Reciprocating Screw Vane Power

85 dBA 76 dBA 76 dBA 7.5 kW

89 dBA 78 dBA 76 dBA 7.6–15 kW

93 dBA 80 dBA 79 dBA 15.1–22 kW

97 dBA 92 dBA 90 dBA 22.1–60 kW

6.103 In noise-sensitive areas, an acoustic enclosure should be included in
the purchase specification for all compressors. Such an enclosure should
produce a reduction of at least 10 dBA in the free field noise level at 1 m.

61


Molecular sieves

6.104 Duplex molecular sieves should be provided in pairs to permit
continuous generation of oxygen. One of the pairs of duplex sieves will be in
the adsorbing stage, whilst the other regenerates.

Dryers

6.105 Air dryers of the desiccant type are usually integrated within the
molecular sieves and therefore do not regenerate independently. Refrigerant
dryers may also be included.

Oxygen monitoring system

6.106 The plant should include a calibrated paramagnetic oxygen monitoring
system comprising oxygen analyser, oxygen concentration indicator, oxygen
flow monitor and oxygen concentration/flow recorder. Connections for
calibration cylinders should also be provided. In the event of the concentration
falling below 94%, the monitoring system should isolate the PSA system from
the pipeline distribution system so that the emergency/reserve manifold goes
into operation. In addition to the above, an independent monitoring system
should be provided to isolate the plant when the concentration falls below
94%. The second system need not be provided with a flow indicator or
recorder.

Operating and indicating system

6.107 The operating and indicating system should perform the following
functions, as appropriate:

a. overall plant control and indication;

b. individual compressor starting;

c. individual vacuum pump starting (where fitted);

d. control of dryers (where installed as separate component);

e. control of molecular sieves;

f. plant status monitoring and indication;

g. optional indication of the plant alarm status (this function may be
considered to be part of the alarm system).

6.108 Provided that the individual compressor starters are housed in a
separate compartment, these functions may be carried out by separate units or
may be installed in a common panel and located on the plant or on the
plantroom wall.

6.109 Control panels containing pneumatic components should have vents to
permit release of pressure in the event of component failure. All functions and
indicators should be appropriately identified and should have a design life of at
least five years. The operating system should be capable of automatically
restarting after reinstatement of the power supply.

6.110 All components of the PSA supply system should be connected to the
standby electrical supply. The control system should ensure that compressors
restart in sequence to avoid overloading the essential power supply.

62


Plant control unit

6.111 The plant control unit should have a separate power supply for each
compressor and vacuum pump, controlled by a separate sub-circuit. The
design should be such that no single component failure in the control unit will
result in loss of plant output.

6.112 The unit should allow either manual selection of duty/standby for each
of the compressors or have an automatic sequence selection with a means for
manual override. The unit should ensure that two or more compressors do not
start simultaneously when power is applied.

6.113 A warning notice which complies with BS 5378 should be affixed
which indicates the presence of low voltage.

The vacuum pump, if provided, forms 6.114 Each compressor should have a selector switch which, when turned to
part of the molecular sieve system. the “on” position, allows the maximum and minimum pressure switches on
the receiver to control the “on” and “off” loading of that compressor. An
alternative “auto” position of the selector switch may allow automatic
selection of the compressors.

Plant control indication

6.115 There should be indicators for each compressor as follows:

a. green “mains supply on”;

b. green “compressor called for” which indicates that the compressor
motor is electrically energised;

c. an indicator of the pressure produced by the compressor.

Compressor and vacuum starter units

6.116 There should be individual starter units for each compressor and
vacuum pump, which should include the features recommended for medical
air compressor plants and vacuum plants respectively.

Molecular sieve control unit

6.117 The molecular sieve control unit may be mounted on the molecular
sieve columns or may be located with the plant control unit. There should be
separate power supplies for the “duty” and “standby” sieve assemblies, taken
from the same phase.

6.118 The molecular sieve control unit should contain the following:

a. a duty selector switch;

b. an on/auto selector switch;

c. individually fused, separate cycling systems for each sieve pair;

d. a system to control regeneration of the sieves in relation to pipeline
demand;

e. an oxygen concentration, dryness sensor and a pressure sensor;

f. an automatic changeover to the standby molecular sieve system, in the
event of failure of the duty unit by oxygen concentration, dryness or
pressure. This requires:

63


(i) electrical and pneumatic isolation of the “duty” sub-assembly so
that it is taken off-stream;
(ii) electrical and pneumatic energisation of the “standby”
sub-assembly so that it is brought on-stream;
(iii) activation of the appropriate fault indicator and associated volt-free
contacts;
(iv) the sub-assembly to remain in this mode of operation until the
fault has been rectified;

g. green function indicators for each dryer sub-assembly to indicate:
(i) molecular sieve 1 selected;
(ii) molecular sieve 2 selected;
(iii) selected molecular sieve – “normal”;
(iv) selected molecular sieve – “failed” (this fault indicator should
remain until manually reset by means of a reset button);

h. a fail-safe system which on failure of the power supply causes the
closure of all inlet, outlet, exhaust and purge valves.

Plant status monitoring

6.119 A monitoring system must be provided to detect the following faults in
the air compressor system:
a. plant faults (for each compressor):
(i) control circuit failed;
(ii) overload tripped;
(iii) after-cooler temperature high;
(iv) compressor temperature high;
(v) compressor run-up time too long;
(vi) activation of other safety devices supplied by the manufacturers;

b. plant faults (for each molecular sieve unit):
(ii) “vacuum pump called for”;
(iii) overload tripped;
(iv) activation of any of the safety devices supplied by the
manufacturer;
(v) oxygen concentration failure;
(vi) pressure fault;

c. plant emergency:
(i) oxygen concentration failed at below 94% concentration;
(ii) receiver pressure 0.5 bar g below the standby cut in pressure;
(iii) dryness above 0.51 mg/m³ (dewpoint –26°C at atmospheric
pressure);

d. pressure fault (cylinder reserve);
(i) pressure in each bank below 50% (of normal cylinder pressure) ;

e. pressure fault (pipeline);
(i) low pipeline pressure;
(ii) high pipeline pressure.

64


Plant status indicator unit

6.120 In addition to the plant control indication, there should be a plant
status indicator panel which may be mounted on the plantroom wall or
adjacent to either the compressor starter unit or the plant control unit. It
should have a warning notice which complies with BS 5378 to indicate the
presence of low voltage.

6.121 There should be indicators for each compressor to show the following
conditions:


b. yellow “control circuit failed”;

c. yellow “overload tripped”;

d. yellow “after-cooler temperature high”;

e. yellow “compressor temperature high”;

f. yellow for each individual safety device provided by the manufacturers;

g. yellow “compressor failure”.

6.122 There should be indicators for each molecular sieve dryer system to
show the following:


b. yellow “oxygen concentration fault”;

c. yellow “pressure fault”;

d. yellow “dryness fault”.

6.123 When the standby dryer is in operation, conditions (b) and (c)
(paragraph 6.122) should be transmitted as a plant emergency to either the
alarm system or to the plant alarm signal status unit.


6.124 An alarm signal status unit should be provided as part of the control
system. It should display the following conditions:

Indication Legend


b. yellow “plant fault” conditions b–f (see 6.121)

c. yellow “plant emergency” condition g (see 6.121)

d. yellow “emergency/reserve low” emergency/reserve banks low<50%

e. yellow plant emergency
“pipeline concentration pressure fault
below 94% O2 fault”

f. red “pipeline pressure fault” pressure fault.

6.125 Conditions (b) to (f) should be transmitted to the central alarm system.
50 V dc, 50 mA.

65


6.126 Alternatively, volt-free, normally closed contacts rated at 5 Vdc, 50 mA
should be provided for transmission of conditions (b) to (f) to the alarm system.

6.127 The panel can be incorporated into the plant indicator unit or be a
be monitored for open/short circuit. In the event of such a cabling fault, a red

6.128 The alarm signal status unit should be supplied from all individual plant
control units, or from a separate common supply.

Plant management

6.129 Connections should be provided which allow monitoring (but not
control) of the plant operation. For example: compressor – on, off, on-load,
unloaded; molecular sieves – on or off. These connections should be used to
provide input to the hospital energy management and building management
systems.

66

7.0 System design – medical air

Compressor systems for medical air 400 kPa

General

7.1 The major components of a medical air system and their layout are
shown in Figure 10. A suitable operating and indicating system is also
required, as specified below. Appropriate layout and adequate siting of these
components should be provided. Package supply systems which should be
specified to meet the requirements given in this memorandum are available
from manufacturers.

Quality

7.2 The required quality level for medical air is specified by
BS EN 132:1991. The requirements for maximum concentrations are given in
Table 1. The European Pharmacopoeia (Ph Eur) specifies maximum impurity
levels for carbon monoxide, carbon dioxide, sulphur dioxide, nitrogen
monoxide and dioxide, moisture and oils. In future, it may be necessary for
provision to be made to control the level of these contaminants and to
monitor the supply to ensure conformance with the specification.

Siting

7.3 The plant should have all-round access for maintenance purposes and
allowance should be made for changing major components.

7.4 The siting of the plant should allow for adequate flows of air for three
different purposes:

a. air intake to the compressors;

b. cooling of the compressed air by the after-coolers;

c. cooling of the compressors.

7.5 Each compressor may require ducting to ensure an adequate flow of
cool air. The manufacturer should be consulted over the range of operating
temperature for which the system is designed.

7.6 Air inlet filters should be fitted immediately upstream of the
compressor. In exceptional circumstances, additional screens, filters and
silencers may be required. The filters should comply with BS 7226:1989 and
be either dry medium filters or grade CA paper element filters.

Compressor noise

7.7 The noise level produced by the compressors will increase with the
capacity of the supply system. The maximum free field noise level for
unsilenced compressed air plant, at 1 m from the plant, varies with the type
and power of the plant but should not normally exceed the following values:

67


(PRV)

with PRV

*

with PRV

* *
Oil Water
† filter separator

Drain*
Oil Water
filter separator

†

Drain*

Bacterial
filter

Notes:
1. Drains marked * are dirty oil/water
2. Filters marked † are activated carbon to
remove smells

Figure 10 Typical medical air 400 kPa system (reproduced by kind permission of MIM)

68


Reciprocating Screw Vane Power

85 dBA 76 dBA 76 dBA 0–7.5 kW

89 dBA 78 dBA 76 dBA 7.6–15 kW

93 dBA 80 dBA 79 dBA 15.1–22 kW

97 dBA 92 dBA 90 dBA 22.1–60 kW

7.8 In noise-sensitive areas, an acoustic enclosure should be included in
the purchase specification for all compressors. Such an enclosure should
produce a reduction of at least 10 dBA in the free field noise level at 1 m.

Air intake

7.9 The air intake for a compressor should be located to minimise
contamination from internal combustion engine exhausts and the discharge
from vacuum systems, anaesthetic gas scavenging systems (AGSS) and
ventilation systems or other sources of contaminants. Ideally, air intakes
should be located at levels of at least 5 m above ground level.

Compressor types

7.10 There are many different types of compressor currently available in the
market. Three types which are most commonly available are:

a. reciprocating piston compressors;

b. rotary vane compressors;

c. rotary screw compressors.

7.11 The compressors may be of any type, provided they are suitable for
continuous running on load and for start/stop operation. If reciprocating
compressors are used they may be either single or two stage, although for a
400 kPa system a single stage compressor is usually satisfactory.

7.12 Compressors for medical air systems are selected by plant
manufacturers from the range of units currently available for industrial users,
and should be selected for their reliability and performance.

Compressor lubrication

7.13 Compressors may be oil-lubricated, provided that suitable
arrangements are made to ensure that the air quality specification given in
Table 1 is fulfilled.

7.14 Rotary compressors are sealed and cooled by oil or water. Oil control
is, therefore, essential and is usually provided as an integral part of the
compressor. Reciprocating compressors may be oil-lubricated, carbon ring,
PTFE ring or diaphragm-sealed type.

7.15 Oil-free compressors may be beneficial in reducing filtration
requirements.

7.16 Where water is used as the sealant, it should be de-mineralised and
the compressor should be provided with suitable feed water pre-treatment,
Such treatment must ensure that there is no risk of microbial contamination
to the air supply. In the event of failure of the water treatment system, the
compressor should automatically shut down to prevent contamination.

69


7.17 There is a danger that PTFE rings and lubricating oils could decompose
at high temperatures to form toxic products. This may be countered by fitting
a temperature sensor to the cylinder head or output of the compressor with
suitable controls to cut off the power supply to the compressors if excessive
temperatures are sensed.

7.18 On start-up, when oil is used as the sealant, moisture condensing at
high pressure forms an emulsion. Once operating temperature is reached,
water is readily separated. Because it is impossible to match the varying
demand with plant capacity, it may be necessary to include oil heating to avoid
emulsification. If it is intended to omit oil heaters, manufacturers should be
asked to confirm the suitability of the compressor for intermittent operation.
Oil-lubricated compressors, however, are considered to be satisfactory.

7.19 Where oil-lubricated compressors are used, suitable means of
separating oil from condensate should be provided.

7.20 Once a compressor installation has been selected:

a. the number required should be left to the supplier of the plant. The
plant should include at least two compressors, but additional
compressors may be included provided that in all cases the total
capacity will provide 100% of system design flow with one compressor
not running;

b. the individual compressors should be arranged so that they will supply
the system simultaneously if necessary;

c. the relative magnitude of the capital and running costs should be
evaluated at the time of purchase. Too much emphasis has been
placed on low capital cost at the expense of reliability and high power
costs. The running costs should be calculated at realistic levels of
usage;

d. the control system for the compressor plant should include an
“hours-run” counter and should be constructed in accordance with the
guidelines given below;

e. the efficiency of plant, expressed as the volume of air delivered to the
pipeline distribution system (after losses in the drying system) per
kilowatt-hour, should be stated by the supplier of the system. The
commissioning procedure should evaluate this efficiency by testing the
power consumption over a suitable period of time at 100%, 10% and
0% of the system design flow. A minimum efficiency of 5 m3/kWh at
100% and 10% is required. The power consumption at zero flow
should be less than 1% of that at 100% design flow.

After-coolers

7.21 After-coolers (and inter-coolers) usually form part of the compressor
sub-assembly. After-coolers should be fitted to oil-lubricated medical air
compressor systems, but may not be required on water-sealed screw
compressors. These will normally be air-cooled and may need ducting with
forced ventilation to ensure an adequate supply of cooling air.

Receivers

7.22 Air receivers should comply with BS 5169:1992 Class 3 and should be
supplied with test certificates. The minimum water capacity of the receivers
should be 50% of the compressor output in 1 minute, stated in terms of free

70


air delivered at normal working pressure. Receivers should also be fitted with
an automatic drain.

7.23 To facilitate the statutory inspection, there should be either two
suitably-valved air receivers, or a by-pass arrangement (for use in manual
operating mode only) in order to avoid interruption to the supply.

Air treatment and filtration

General

7.24 Contaminants can enter the compressed air system from three sources:
the atmosphere, the compressor and the pipeline distribution system. Each
potential source must be taken into account when specifying the type and
location of air treatment equipment. Filtration equipment may include pre-
filters, coalescing filters, carbon filters, particulate filters and any other
additional filtration equipment necessary to provide the appropriate quality.

Solid contaminants

7.25 Dirt particles in the environment cover a wide range of sizes, but
approximately 80% are less than 0.2 µm and are therefore not removed by
the intake filter to the compressor.

7.26 Although particles smaller than 40 µm are unlikely to cause mechanical
damage, a 5 µm intake filter is preferred, to avoid blockage of internal air/oil
separators.

7.27 There are a number of methods for measuring particle size and
concentration, such as cascade impactors, particle counters, light dispersion
photometers, laser counters etc. None of these is suitable for sampling from a
compressed air pipeline.

7.28 Filters are specified in terms of performance tests, for example, sodium
flame test, DOP test, etc.

Water

7.29 Water is always a contaminant in a compressed air system, regardless
of the type and location of the compressor plant, since the air drawn into the
compressor intake is never completely free of water vapour. The amount can
vary from 2.5 g/m3 to over 40 g/m3, depending on the climatic conditions.
Some of this is removed by the after-cooler and receiver, but about 20 g/m3 is
likely to remain in the compressed air unless removed by dryers.

7.30 A water content to not exceed 115 VPM (0.095 mg/l equivalent to
dewpoint –40°C at atmospheric pressure) is specified for medical air pipeline
systems. This can usually only be achieved by desiccant dryers; refrigeration
dryers can only perform satisfactorily down to a pressure dewpoint of about
+3°C and are therefore not recommended as the sole form of drying.

Oil

7.31 With oil-lubricated compressors, it is inevitable that the compressed air
contains oil. Even with oil-free compressors (non-lubricated), complete
freedom from oil and oil vapour cannot be positively guaranteed, as

71


hydrocarbon vapours may be drawn into the compressor. Oil levels in the air
supply must be controlled to 0.1 mg/m3, with means of monitoring on a
routine basis.

7.32 Oil will exist in the system in three forms: bulk liquid, oil aerosol and oil
vapour. Provided that the oil lubricant is appropriate and the after-cooler
properly designed, the amount of oil present as vapour should be small and is
unlikely to exceed 0.5 mg/m3.

7.33 The amount of oil present as bulk liquid and aerosol present in a
compressed air system is more difficult to predict. With modern, well
maintained oil lubricated compressors it is unlikely to exceed 5 mg/m3 due to
the high efficiency oil/air separator.

7.34 Oil-contaminated compressor condensate is classified as a trade effluent
by virtue of section 14 of the Public Health (drainage of trade premises) Act
1937. An oil condensate separator should therefore be installed.

7.35 Under the Water Resources Act 1991 section 85, it is illegal to make The maximum limits of oil in water are
a discharge of trade effluent to “controlled waters” via a surface water drain from 5 mg/l up to 15 mg/l
without the consent of the National Rivers Authority.

7.36 Similarly, under the Water Industries Act 1991, Regional Water Maximum limits range from region to
Authorities enforce the limit of oil condensate discharged into the public region, from 25 mg/l up to 500 mg/l;
foul sewer. Prior consent to discharge is mandatory. the local Water Authority should be
consulted
7.37 Condensate from oil-free compressors may be discharged to drain.

7.38 Any condensate produced from the compressor/dryer system must be
regarded as trade effluent, and is therefore not suitable for discharge to any
surface water system draining to any surface water sewer, water-course or
soak away; this may not apply if a suitable separator is installed.

Dryer controls

7.39 The dryer control system should ensure that regeneration is operated in
proportion to the compressed air usage. The effectiveness of the control
system will become apparent when the efficiency of the compressor system is
tested at 10% and 0% of the system design flow. Evidence of the reliability
and performance of a dryer system should be sought from manufacturers,
since these items are critical to the overall performance of the compressor
system. The dryer control system should include a dewpoint meter.

Dust filters

7.40 There should be a dust filter downstream of the dryers to remove
particles down to 1 µm, with a DOP penetration of less than 0.03%, when
tested in accordance with BS 3928.

7.41 Each dryer and filter assembly should be rated for continuous use at the
system demand flow, with air at 100% relative humidity at 35°C.

Activated carbon filter

7.42 Duplex activated carbon filters should be installed upstream of the final
bacterial filter.

72


Bacteria filters

7.43 Duplex bacterial filters should be fitted upstream of the final pressure
regulator with appropriate isolating valves. The filters should provide particle
removal to 0.01 mg/m3 and a DOP penetration of less than 0.0001%.

Pressure control

7.44 The pressure control should maintain the nominal pipeline pressure
within limits given in Appendix K. Duplex line pressure regulators should be
provided with suitable isolating valves. The regulators should be of the
non-relieving type.

Test point

7.45 A test point comprising shut-off valve and terminal unit should be
provided to permit sampling of the medical air quality.

Safety valves

7.46 Safety valves should be provided in accordance with the system
requirements given below. All safety valves should conform to BS 6759
Part 2:1984. A safety valve of the certified discharge capacity stated should be
fitted in each of the following positions:

a. on the delivery pipe of each compressor and upstream of any isolating
valve, non-return valve or after-cooler, capable of discharging the total
throughput of the compressor;

b. on each air receiver and dryer tower, capable of discharging the sum of
the throughput of all the compressors. It is not necessary to provide
safety valves on the dryer columns where the system is already
protected by a safety valve on the receiver and the downstream
equipment, that is, if the dryer column is already sufficiently protected;

c. immediately downstream of each pressure regulator, capable of
discharging the system demand flow.

7.47 All safety valves should be of the closed bonnet type and connected to
suitably-sized pipework to allow safe discharge, not necessarily to the outside.
The set pressure of the safety valves should be as given in Appendix K.

Traps and valves

Automatic drainage traps

See paragraphs 7.34 to 7.39 for 7.48 Electrically or mechanically operated automatic drainage traps should
effluent discharge requirements be provided on the after-coolers, receiver, separators and coalescing filters.
The discharge from these drainage traps should be piped to a suitable gulley.
Co-ordination with building work is required for this provision.

7.49 Drainage and tun-dishes are usually provided under the building
contract. Separators should be provided under the air compressor contract.
Provision of interceptor tanks may be provided under either the building
contract or the air compressor contract, as appropriate.

73


Non-return valves

7.50 Non-return valves are required to prevent backflow of the air supply in
certain situations. These valves should be located as follows:

a. between the compressor and the receiver, but downstream of any
flexible connector;

b. downstream of the dust filter on the dryer;

c. upstream of the emergency cylinder reserve connection in the pipeline
connecting the plant to the pipeline distribution system, to prevent
back feeding this plant;

d. upstream of any inlet point which may be used to feed the system in
an emergency;

e. downstream of the emergency cylinder manifold regulators.

Isolating valves

7.51 Isolating valves should be provided downstream of non-return valves
and upstream of, for example, the connection of the emergency reserve
manifold. Isolating valves should be provided in order to facilitate maintenance
or replacement of plant items.

7.52 Manually-operated ball isolation valves should be located in the
positions shown in Figure 10, to allow isolation of components such as
receivers, dryers, automatic drains, pressure regulators and filters. There should
also be a valve on the compressed air plant, upstream of the non-return valve
and the connection of the emergency cylinder reserve.

Pressure indicators

7.53 Pressure indicators should comply with BS 1780:1985 (1992), or have
an equivalent performance if electronic indicators are used. Calibration should
be in bar g or kPa. All gauges should have a minimum scale length of 90 mm,
and the working range should not exceed 65% of the full scale range, except
on differential pressure gauges. Where digital gauges are provided, the height
of the display should not be less than 14 mm. Pressure indicators should be
connected by means of gauge cocks.

7.54 Pressure indicators should be located:

a. on the plant control unit indicating receiver pressure;

b. on each receiver;

c. downstream of each pressure regulator;

d. on each dryer tower;

e. on the plantroom pipework, downstream of the plant isolating valve;

f. on the test point.

7.55 Differential pressure indicators should be located on:

a. each coalescing filter;

b. each dust filter;

c. each bacterial filter;

or any combination, as appropriate.

74


7.56 All control devices should be connected directly to the pipework via a
minimum leak device (to allow removal for servicing) and not isolated by
valves. Gauges should be isolated for maintenance purposes by gauge cocks.

Operating and indicating system

functions:


b. individual compressor starting;

c. control of dryers;

d. plant status monitoring and indication;

e. indication of the plant alarm status.

7.58 Provided that the individual compressor starters are housed in a
separate compartment, these functions may be carried out by separate units
or may be installed in a common panel and located on the plant or on the
plantroom wall. Control panels containing components should have vents to
permit release of pressure in the event of component failure. All indicators
should be appropriately identified and should have a design life of at least one
year.

7.59 The operating system should be capable of automatically restarting
after reinstatement of the power supply.

7.60 All components of the medical air supply system should be connected
to the standby electrical supply. The control system should ensure that
compressors restart in sequence to avoid overloading the essential power
supply.

Plant control unit

7.61 The plant control unit should have a separate power supply for each
compressor, controlled by a separate sub-circuit.

of the compressors or have an automatic sequence selection with a means for
manual override. The unit should ensure that two or more compressors do not
start simultaneously when power is applied.

7.63 A warning notice which complies with BS 5378 should be affixed
which indicates the presence of low voltage.




b. green “compressor called for” which indicates that the compressor
motor is electrically energised;
c. an indicator of the pressure produced by the compressor.

75


Compressor starter units

7.65 There should be individual starter units for each compressor which
operate a single designated compressor. The starters should be provided with
safety interlocks, as specified by the compressor manufacturers, which should
inhibit plant operation until manually reset by means of a button. The starters
should allow automatic restart after an interruption to the power supply. Each
starter unit should contain the following:

a. an isolator interlocked with the covers;

b. either HRC fuses to BS 88 or suitable circuit breakers to BS EN 60947-2
and/or BS EN 60898;

c. an industrial grade ammeter to BS 89;

d. a “total hours” counter if not included in the plant control unit;

e. a green “mains supply on” indicator if mounted separately from the
plant control unit.

Dryer control unit

7.66 The dryer control unit may be mounted on the dryers or may be
located with the plant control unit. There should be separate power supplies
for the “duty” and “standby” dryer assemblies taken from the same phase.

7.67 The dryer control unit should contain the following:

a. a duty dryer selector switch;

b. a service function – to enable selection of continuous/normal running;

c. individually fused, separate cycling systems for each dryer;

d. a system to control regeneration of the dryers in relation to pipeline
demand;

e. a dewpoint meter and a pressure sensor;

f. an automatic changeover to the standby dryer system in the event of
failure of the duty unit by either dryness or pressure. This requires:
(i) electrical and pneumatic isolation of the “duty” sub-assembly so
that it is taken off-stream;
(ii) electrical and pneumatic energisation of the “standby”
sub-assembly so that it is brought on-stream;
(iii) activation of the appropriate fault indicator and associated volt-free
contacts;
(iv) the sub-assembly to remain in this mode of operation until the
fault has been rectified;

g. green function indicators for each dryer sub-assembly to indicate:
(i) dryer 1 selected;
(ii) dryer 2 selected;
(iii) selected dryer – “Normal”;
(iv) selected dryer – “failed” (this fault indicator should remain until
manually reset by means of a reset button);

h. a fail-safe system which on failure of the power supply causes the
following:
(i) closure of the exhaust and purge valves;
(ii) opening of the inlet and outlet valves.

76



7.68 A monitoring system should be provided to detect the following faults
in the air compressor system:

a. plant faults (for each compressor):
(ii) motor tripped;
(iii) after-cooler temperature high;
(v) compressor failed to go on load;

b. plant faults (for each dryer unit):
(i0 dryer failure;
(ii) pressure fault;

c. plant emergency:
(i) receiver pressure 0.5 bar below the standby cut in pressure;
(ii) receiver pressure 0.5 bar above cut out pressure;
(iii) dryness above 0.51 mg/m³ (dewpoint at -26°C at atmospheric
pressure);
d. pressure fault (cylinder reserve):
(i) pressure in duty bank below 50% (of normal cylinder pressure);

e. pressure fault (pipeline):



conditions:








7.71 There should be indicators for each dryer system to show the
following:


b. yellow “dryness fault”;

c. yellow “pressure fault”.

77




Indication Legend


b. yellow “plant fault” conditions (b–g), see 7.70;
(c), see 7.71

c. yellow “plant emergency” low reservoir pressure; high
moisture, that is, condition (b),
see 7.71

d. yellow “reserve low” emergency/reserve banks low
(<50%)


50 V dc, 50 mA.

7.74 Alternatively, volt-free, normally closed contacts rated at 50 V dc,
50 mA should be provided for transmission of conditions (b) to (e) to the alarm
system.

7.75 The panel can be incorporated into the plant indicator unit, or be a


Plant management

7.77 Connections should be provided which allow monitoring of plant alarm
conditions (b) to (e) and pump running for each “compressor”. These
connections should be volt-free contacts normally closed for each condition
having a minimum rating of 50 V dc, 50 mA. The building management
system should not be used to control the plant.

Operating considerations

7.78 Plant should be operated in accordance with the manufacturer’s
instructions and covered by a sound, effective, planned preventative
maintenance (PPM) policy.

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Synthetic air

General

7.79 This section gives technical details of the process and systems required
to generate medical air from mixing gaseous oxygen and nitrogen, derived
from a cryogenic supply.

7.80 For the purposes of the Medicines Act, it is considered that the
synthetic air is manufactured on-site, for use on that site only, in exactly the
same way as for medical air derived from compressor plant.

7.81 The production of synthetic air implies a manufacturing process, and
as such the process should be subjected to the same safety requirements as
for a pharmaceutical process. This should include, for example, a HAZOP
analysis and other safety analyses which may be necessary.

7.82 Synthetic air is generated by mixing gaseous oxygen and nitrogen in a
blender or mixing panel at pre-set pressures to ensure that the resultant
mixture is always correct. Continuous on-line monitoring of oxygen
concentration is provided to check the mixture; the system shuts down
automatically in the event of out-of-specification concentration.

7.83 In the event that one mixing systems shuts down, the pipeline is
supplied from the back-up mixing system to ensure continuity of supply.

7.84 The feasibility study should provide more information on the details of
the monitoring and alarm systems required, as well as operational
information.

7.85 The vacuum insulated evaporator (VIE) system supplying the medical
oxygen may be used to supply the synthetic air system, depending on the
actual system demands.

7.86 Nitrogen supplied to the synthetic air system may also be used to
provide the power source for surgical tools instead of surgical air at 700 kPa.

7.87 An electrical power supply is required in order, for example, to operate
solenoid valves and monitoring instrumentation. Therefore the system should
be on the essential power supply and connected via an uninteruptable power
supply (UPS) with at least 4 hours’ capacity. This should ensure continuity of
supply in the event of power failure.

System description

7.88 The gaseous oxygen and nitrogen are derived from bulk liquid supplies
contained in a VIE – as described in the “Liquid oxygen supplies” section of
Chapter 6.

7.89 The oxygen for synthetic air may be taken from the VIE supplying the
medical oxygen system or it may be from a dedicated VIE. It would normally
be more cost-effective for the oxygen to be taken from the main VIE,
although this would obviously depend on the existing VIE capacity, the
demand, space constraints etc. The feasibility study should provide more
detailed information on whether it is likely to be more cost-effective to
provide a totally separate VIE system or to use the existing medical oxygen
VIE.

79


Figure 11 Typical synthetic air layout – oxygen VIE supply (reproduced by kind permission of BOC)

80


Figure 12 Typical synthetic air layout – nitrogen VIE supply with air mixing equipment (reproduced by kind permission
of BOC)
81


7.90 For both the oxygen and nitrogen it is necessary to have a back-up
system. Since it is essential to ensure continuity of supply, the system demands
are such that this back-up should be derived from a second, smaller VIE.

7.91 This second back-up VIE can also provide the back-up to the medical
oxygen system, thus providing a more realistic back-up facility than the cylinder
manifolds currently installed.

7.92 Since four VIEs will be required (although two of them will be relatively
small), there will of necessity be space requirements to be considered when
planning the installation of a synthetic air system.

7.93 The system comprises:

a. storage vessels – one main vessel and one back-up vessel for both
oxygen and nitrogen;

b. vaporizers for both oxygen and nitrogen ;

c. medical oxygen flow control – where used to supply medical oxygen
systems;

d. surgical nitrogen flow control – where required;

e. control panel for the nitrogen and oxygen supplies to the mixing
panels;

f. duplicate air mixing panels;

g. buffer vessels – each mixer has a buffer vessel to smooth fluctuations
in demand;

h. warning and alarm system;

j. duplicate oxygen analysers on each mixer.

7.94 The system is shown in Figures 11 and 12, which are provided courtesy
of BOC and are copyright.

Storage vessels

Vessel summary

7.95 The following vessels are required:

a. one main oxygen vessel;

b. one standby oxygen vessel with 24 hours’ capacity;

c. one main nitrogen vessel;

d. one standby nitrogen vessel with 24 hours’ capacity.

Vessel operating pressure

7.96 The following operating pressures are required:

a. main vessels 12.5 bar g;

b. back-up vessels 12.5–14 bar g.

82


Main vessel capacity

7.97 The main vessel should normally be sized on the basis of 2 weeks’
supply. This should be calculated as 14 x the average daily usage. This should
provide adequate storage and a cost-effective vessel filling regime. The gas
supplier should, however, be consulted as there may be other factors, such as
geographical location, space etc, which need to be taken into account when
sizing the main vessels.

Back-up vessel capacity

7.98 The standby vessel should have 24 hours’ capacity at any time, that is,
it should be sized on the basis of twice the average daily usage. This will
ensure that there is always 24 hours’ supply available.

7.99 In addition to the normal instrumentation as set out in the “Liquid
oxygen supplies” section of Chapter 6, the vessels should be fitted with a
telemetry system to continuously monitor the vessel contents.

7.100 This information should be transmitted direct to the gas supplier and
also the hospital. The exact details of how much information, and where it
should be received, will depend on each hospital site.

7.101 The main vessel low level alarm is activated at 25% full; the back-up
low level alarm is activated at 50% full.

7.102 The safety relief valves and bursting discs should be sized in
accordance with the BCGA Code of Practice.

7.103 The liquid from the vessels should be supplied to the process at a
nominal pressure of 12.5 bar g.

Vaporisation

7.104 The main and standby vessels should have dedicated vaporisers
designed for continuous capacity and 24 hour capacity respectively at
1.5 x the required flows to ensure that the vaporisers are not overdrawn.

7.105 This may be achieved in each case by either a single set of vaporisers,
or by vaporisers operated on timed or manual changeover.

7.106 It is preferable for the vaporisers to operate on a timed changeover as
this minimises the maintenance actions which the hospital are required to
carry out.

7.107 The timed changeover will require a 110V or 240V supply; this should
be on the emergency supply and an uninterruptible power supply should also
be provided with at least 4 hours’ capacity.

7.108 Each isolatable vaporiser or set of vaporisers must have a safety relief
valve.

Medical oxygen flow control

7.109 A control panel (similar in principle to a C11 panel) should be provided
– the only difference is that the standby supply is from a low-pressure liquid
source, instead of high-pressure cylinders.

83


Surgical nitrogen flow control

7.110 A control panel to regulate the gaseous nitrogen to between 7.5 and
9.5 bar g, depending on the system design, should be provided.

7.111 The pipeline distribution system should be designed in exactly the same
way as for surgical air 700 kPa systems, as described in Chapter 8.

Control panel for the nitrogen and oxygen supplies to the mixing
panels

7.112 The control panel should be sized in order to provide pressure
regulated flows as appropriate for the mixing system; this would typically be
up to 200 Nm3/hr.

7.113 The standby supply regulation cuts in when the main line pressure falls
to 11 bar g; there is no regulation on the main supply line.

7.114 A non-return valve should be installed in both the nitrogen and oxygen
supply lines within the mixer to prevent cross contamination.

7.115 A non-return valve should also be installed on both the main oxygen
supply and the standby oxygen supply to the mixer to prevent the medical
oxygen line becoming contaminated with nitrogen.

Air mixing panels

7.116 A range of sizes of mixing panels are available with, typically, nominal
capacities of 50, 100 and 200 Nm3/hr.

7.117 A regulated supply of nitrogen and oxygen is mixed in a mixing valve.
The differential pressure at the inlet to the mixing panel is critical and should
not exceed 0.5 bar g. A pressure switch operated solenoid valve opens and
shuts on a 0.5 bar g differential.

7.118 The main mixer solenoid valve opens when the line pressure falls to
4.2 bar g; the standby mixer solenoid valve will open if the line pressure
continues to fall to 4.0 bar g.

7.119 Two independent paramagnetic oxygen analysers are provided on each
mixer to give continuous on-line measurements.

7.120 If the oxygen concentration falls outside 20–22% as measured by either
analyser, the mixer solenoid valve is held closed and the mixer is shut down. In
addition, a signal is relayed downstream to close the solenoid valve on the
buffer vessel associated with that mixer.

Buffer vessels

7.121 Each mixer has associated with it a buffer vessel to smooth fluctuations
in demand.

7.122 In the event that the oxygen concentration is outside the specification,
that is, 20–22%, the solenoid valve downstream of the buffer vessel will also
close, preventing air from the buffer vessel from entering the distribution
system.

84


7.123 The buffer vessel, together with appropriate safety relief, should be
sized to match each mixing panel to provide stable operation.


7.124 The same alarm conditions for liquid oxygen should also be
transmitted and displayed for the liquid nitrogen system. The following
conditions should be displayed for the mixing panels:

Indication Legend


b. yellow “plant fault” low gas pressure to any mixer

c. yellow “plant emergency” analysis out of specification on any mixer

d. yellow “reserve low” operating on final mixing panel/buffer
vessel only

e. red “pressure fault” pressure fault.

Where relays are used, they should be normally energised relays which de-
energise under fault conditions, with contacts having a minimum rating of
50 V dc, 50 mA.

50 mA should be provided for transmission of conditions (b) to (e) to the
alarm system

7.127 The panel can be incorporated into the mixing panel control unit, or
be a separate unit within the plantroom. If mounted separately, the cabling
should be monitored for open/short circuit. In the event of such a cabling
fault, a red “system fault” lamp should be illuminated on the alarm signal
status unit, together with the appropriate alarm condition.

Emergency supply facility

7.128 This may be appropriate on some sites. A risk assessment should be
carried out to establish the vulnerability of the main supply system of both
oxygen and nitrogen.

7.129 An emergency supply facility may be either:

a. a medical air compressed gas manifold located away from the main
supply within the hospital;

b. portable emergency manifolds on trolleys.

85

8.0 System design – surgical air 700 kPa

General

8.1 Surgical air at 700 kPa is only used as the power source for surgical
tools. These tools typically require high flows – up to 350 l/min – at 700 kPa at
the point of use. Where nitrogen is available on site, it may be used as an
alternative source of supply.

8.2 Supply systems for surgical compressed air may be a cylinder manifold
system, a dedicated 700 kPa compressor system or a compressor system
capable of supplying both the 700 kPa and the 400 kPa supplies. In practice,
the decision about which compressor system to install needs careful
consideration due to the flow rates required and total usage.

8.3 Cylinder manifold systems would normally be the most appropriate
supply system; a compressor system would only be required for large theatre
complexes specialising in orthopaedic and/or neurosurgery, and thus
necessitating a high use of pneumatically powered surgical tools.

8.4 It is possible to use nitrogen instead of air as the power source for
surgical tools. This may be derived from either a liquid source or cylinders. In
either case, the terminal units will need to be different from the existing
medical air 700 kPa terminal units. A non-interchangeable screw thread (NIST)
connector is already specified for nitrogen and should be used.

8.5 The pressure control unit should comprise a regulating valve with
upstream and downstream pressure gauges.

8.6 Whatever supply system is installed, the overall system should be
designed to provide a minimum of 700 kPa at the front of each terminal unit
at a flow of 350 l/min.

8.7 The maximum pressure under “no flow” or “low flow” conditions
should not exceed 9 bar g.

8.8 Cylinders of medical air should always be available for use in an
emergency.

Cylinder manifold supply systems

8.9 These should generally be based on the systems described for medical
air cylinder manifold systems in Chapter 5, except that the emergency/reserve
supply will not normally be required and the alarm system will be much
simpler.

8.10 The alarm conditions should be transmitted to the central alarm system
to alert porters and other staff of the need to change cylinders.

86


Compressor supply systems

8.11 These should generally be based on the requirements for medical air
400 kpa systems given in Chapter 7, and the quality of the delivered surgical
air should be the same as medical air, as specified in paragraph 2.10.

8.12 It is not necessary to provide duplex systems, since surgical air is not
used for life support systems. It may, however, be considered appropriate to
provide a simple standby manifold for larger installations. To avoid confusion
with the emergency/reserve cylinders supplies for 400 kPa systems, the
surgical air standby system for 700 kPa systems, where provided, is referred to
as a back-up system.

Operating and alarm system – cylinder manifold
supply system

Manifold monitoring and indicator system

8.13 The monitoring and indicator system should perform the following
functions:

a. overall manifold monitoring;

b. manifold condition indication;

c. overall supply plant indication.

All functions should be appropriately identified.

Manifold monitoring

8.14 The manifold should be monitored to detect the following:

a. duty bank operating;

b. duty bank empty and standby operating;

c. standby bank below 10% capacity when duty bank is empty.

Manifold indicator unit


a. a green “running” indicator;

Conditions (b) and (c) are the same b. a yellow “empty” indicator for each bank when the running bank is
empty and the reserve is in use;

c. a yellow “low pressure” indicator for each bank when changeover has
occurred and the pre-set low pressure has been reached.

87




Indication Legend

a. a green “normal” normal

b. a yellow “duty bank empty, standby
running” condition change cylinders

c. a yellow “duty bank empty, standby low”
condition change cylinders
immediately

d. a red “pipeline pressure fault”
indicator pressure fault

8.17 Conditions (b) to (d) should be transmitted to the central alarm system.
50 V dc, 50 mA.

system.

8.19 The panel can be incorporated into the manifold indicator unit or be a

Compressor supply system

8.20 The compressor operating system should be based on the
recommendations for 400 kPa compressor systems, except that simplex plant
operation only would be required.


8.21 A monitoring system should be provided to detect the following faults
in the air compressor system:

a. plant faults for each compressor:
(ii) motor tripped;
(iii)` after-cooler temperature high;
(v) compressor failed to go on load;

b. plant faults for each dryer unit:
(i) dryness failure (dewpoint meter > –26°C);
(ii) pressure fault;

c. plant emergency:
(i) receiver pressure 0.5 bar g below the standby cut-in pressure;

88


(ii) receiver pressure 0.5 bar g above cut-out pressure ;
(iii) dryness above 0.51 mg/l (dewpoint at –26°C at atmospheric
pressure);

d. pressure fault (cylinder reserve):
(i) pressure in duty bank below 50% (of normal cylinder pressure);

e. pressure fault (pipeline):



conditions:








8.24 There should be indicators for each dryer system to show the
following:

b. yellow “dryness fault”;

c. yellow “pressure fault”.



Indication Legend


b. yellow “plant fault” conditions (b–g), see 8.23;
(c),see 8.24

c. yellow “plant emergency” low reservoir
pressure; high moisture,
ie condition (b), see 8.24

d. red “pipeline pressure fault” pressure fault.

89


8.26 Conditions (b) to (d) should be transmitted to the central alarm system.
50 V dc, 50 mA.

50 mA should be provided for transmission of conditions (b) to (d) to the alarm
system.

8.28 The panel can be incorporated into the plant status indicator unit or be
a separate unit within the plantroom. If mounted separately, the cabling
should be monitored for open/short circuit. In the event of such a cabling fault,
a red “system fault” lamp should be illuminated on the alarm signal status
unit, together with the appropriate alarm condition.


Plant management

8.30 Connections should be provided which allow monitoring, but not
control, of plant alarm conditions (b) to (e) and pump running for each
“compressor”. These connections should be volt-free contacts normally closed
for each condition having a minimum rating of 50 V dc, 50 mA. The building
management system should not be used to control the plant.

Operating considerations

instructions and covered by a sound, effective, planned preventative

Simplex plant

8.32 The same philosophy should be applied to simplex plant as for medical
air compressor plant, except that no standby compressor, dryer system or
emergency/reserve manifold or cylinders will be required.

90

9.0 System design – medical vacuum supplies

General

9.1 The medical vacuum pipeline system provides immediate and reliable
suction for medical needs, particularly in operating theatres.

9.2 The medical vacuum pipeline system consists of the vacuum supply
system, the distribution pipework and terminal units. The performance of the
pipeline system is dependent on the correct specification and installation of its
component parts. This section describes the requirements of the vacuum
supply system.

9.3 The medical vacuum pipeline system should be designed to maintain a
vacuum of at least 300 mm Hg (40 kPa) at each terminal unit during the
system design flow tests; see Appendix G.

9.4 To ensure continuity of supply, the vacuum plant should be connected
to the essential electrical power supply.

9.5 The capacity of the vacuum supply system should be appropriate to
the estimated demand. Observations of the capacity actually used (in terms of
hours run by vacuum plant) in existing systems show clearly that the system
design flow calculations for most hospitals have been in excess of actual
demand. An appropriate reduction in capacity may be undertaken in an
existing hospital by installing a vacuum supply system based on the design
criteria in Chapter 4 when replacement is due. This could lead to considerable
savings in capital investment and the release of plantroom floor space.

9.6 With the exception of the vacuum discharge to atmosphere, the
pipeline distribution system for vacuum has traditionally been constructed of
copper. PVC pipework can be considered where cost-effective. Pressure
testing of PVC pipework should be carried out at 100 kPa.

9.7 The major components of a medical vacuum system and their layout
are shown in Figure 13. A suitable operating and indicating system with
alarms is also required. Appropriate layout and adequate siting of these
components should be provided. Packaged supply systems are available from
manufacturers which should be specified to meet the requirements given in
this memorandum.

9.8 The plant should consist of at least two identical pumps, a vacuum
reservoir with by-pass facilities, two duplex bacteria filters with drainage traps,
appropriate non-return valves, isolating valves, gauges and pressure switches,
an operating and indicating system, an exhaust system and a test point.

Siting

9.9 The plant should have all round access for maintenance purposes and
allowances should be made for changing major components.

9.10 The siting of the plant should allow for adequate flows of air to cool
the pumps. The manufacturers should be consulted over the range of

91


Figure 13 Schematic diagram of a typical medical vacuum system (reproduced by kind permission of MEDÆS)

92


operating temperature for which the supply system is designed. In extreme
cases, refrigerator cooling may be required.

Pump noise

9.11 The noise level produced by the pumps will increase with the capacity
of the supply system. For larger systems this can result in an unacceptable
noise level at the pump. The maximum free field noise level at 1 m from the
unsilenced pump should not exceed the following values for individual pumps:

Power Noise Level

5 kw 75 dBA

5.1–15 kW 82 dBA

15 kW 89 dBA.

9.12 A suitable acoustic enclosure may be required in the purchase
specification for all pumps with a free field noise level at 1 m of 80 dBA or
over. An enclosure should produce a reduction of at least 10 dBA in the free
field noise level at 1 m.

Vacuum plant exhaust

9.13 The position of the termination point should be carefully chosen to be
clear of windows, ventilation intakes and the intake of air compressors and
other equipment, since for oil-lubricated pumps the vacuum exhaust is likely
to be polluted with oil fumes.

9.14 Noise from the exhaust should be considered and a silencer fitted.

9.15 The construction should conform to the following criteria:

a. the exhaust should be sized to give a back pressure at system design
flow which is matched to the pump performance;

b. the termination point should be provided with protection, to reduce the
effect of wind pressure and prevent the ingress of rain, snow, insects or
animals;

c. weatherproof notices should be fixed at the discharge point(s) with the
legend “medical vacuum discharge point – do not obstruct”;

d. the exhaust pipe should be provided with a drainage valve at its lowest
point;

e. a silencer should be fitted on the exhaust pipe from each pump. This
may be integral with the pump unit.

Efficiency

9.16 The efficiency of the plant should be measured at 100% and 10% of
system design flow. The efficiency should not be less than 200 l/min of free
air aspirated, corrected to STP per kilowatt of electricity used when the pump
is equilibrated at normal operating temperature and whilst maintaining
pressure of 450 mm Hg (60 kPa). The pump should be capable of producing a
higher vacuum than that required in the pipeline, so that the resistance of the
bacteria filter and back pressure in the exhaust system can be overcome. For
this purpose the pump should be capable of providing a vacuum of not less
than 650 mm Hg (87 kPa).

93


9.17 The capacity of the vacuum pump should be specified in terms of the
free air aspirated (FAA) in l/min when the pump is operating at a vacuum of
475 mm Hg (63 kPa) and at 450 mm Hg (60 kPa) at the plant pipeline
connection. The performance of any pump is a curve which varies between a
negligible FAA at the maximum vacuum, and maximum FAA at the
atmospheric pressure, so that the capacity of any pump depends on the
vacuum at which it is operating. If a single FAA capacity value is quoted for a
vacuum pump, it has no meaning unless it is referred to a single vacuum
setting. A pump should be chosen which has a good performance curve in the
range 500–650 mm Hg (67–87 kPa).

Vacuum pumps

9.18 Vacuum pumps for medical vacuum plants are selected by plant
manufacturers from the range of units currently available for industrial use.
New designs of vacuum pumps continue to appear on the market. Any type of
pump may be used provided it meets the requirements of performance,
efficiency and reliability which are given here.

9.19 Water-sealed pumps should not be used.

9.20 Rotary vane pumps are available from several manufacturers and have
replaced reciprocating vacuum pumps which are now obsolete. Many different
models are available, with performance characteristics which are optimised for
different uses. Vacuum pumps for MGPS should be chosen for reliability under
stop/start use.

9.21 Pumps should normally be oil-lubricated. Vapours from the lubricating
oil are unlikely to be a significant component of the exhaust gases if correctly
maintained. “Dry running” rotary vane pumps are available at increased capital
cost and with lower efficiency than oil lubricated pumps of comparable
performance.

9.22 At least two pumps should be provided. The actual number is at the
discretion of the plant manufacturer to ensure optimum cost benefit of the
system. In all cases, the total capacity must be at 75% of the system design
flow with one pump not running. All pumps should be designed for
continuous operation.

9.23 All systems should comprise pumps and motors of identical type which
are suitable for continuous running and stop/start operation.

9.24 Pump motors should comply with the National Health Service Model
Engineering Specification C51 with the addition of Class F insulation and Class
B temperature rise.

9.25 A vacuum reservoir should be provided so that the duty pump does not
run continuously for low loads. The reservoir should be manufactured in
accordance with BS 5169 for class III, with test certificates provided to the
user. The minimum test pressure should be 4 bar g.

9.26 The water capacity of the reservoir should be equal to the plant design
flow at 450 mm Hg (60 kPa), in terms of free air aspirated in 1 minute with
the pump operating at 450 mm Hg (60 kPa).

9.27 Provision should be made for draining the reservoir under vacuum
conditions. By-pass facilities should be provided so that the reservoir can be
drained and inspected without interruption to the vacuum supply. The reservoir
should be fitted with suitable lifting lugs and feet.

94


9.28 If multiple reservoirs are provided, they should be arranged in parallel.

9.29 The bacteria filters and drainage trap should comprise two identical
sub-assemblies with manually operated isolating valves, arranged to allow
either sub-assembly to be on stream. Each sub-assembly should contain a
bacteria filter rated at the plant capacity.

9.30 The bacteria filter should be marked with the legend “bio-hazard”,
together with a description of a safe procedure for changing and disposing of
the filters and emptying the drainage trap.

9.31 The bacteria filters should have a filter efficiency, when tested by the
sodium flame test in accordance with BS 3928:1969, of less than 0.005% at
the system design flow.

9.32 The pressure drop across a clean filter at the system design flow
should not exceed 25 mm Hg (3 kPa) at a vacuum of 475 mm Hg (63 kPa).

9.33 The drainage trap may be integral with the bacteria filter and should
be fitted with a transparent sterilizable bowl to collect liquid.

Precautions for changing filters are 9.34 Microbial contamination – whereas there is no firm evidence which has
included in the ‘Operational demonstrated the need for bacteria filters, it is recommended that such
management’ volume of this HTM devices are included as precautionary measures.

Pressure control

9.35 The cut-in setting for the vacuum pumps should be adjusted to allow
for the pressure drop across the pipeline distribution system and the bacteria
filters. The cut in may be expected at about 500 mm Hg (67 kPa).

9.36 The cut-out setting should be at an appropriate point on the
performance curve of the pump, which minimises stop/start operation but is
at a vacuum which is economically attained by the pump. This cut-out setting
may be expected at about 650 mm Hg (87 kPa).

Valves

9.37 Non-return valves should be fitted, when necessary, at the inlet and
outlet of each pump to prevent backflow when a common discharge pipe is
used. (Some vacuum pumps include integral non-return valves.)

9.38 Manually operated valves should be arranged in the positions shown in
Figure 13, to allow isolation of components such as pumps, reservoirs, by-pass
pipework, drainage taps and bacteria filters.

Pressure regulation of vacuum system

9.39 A vacuum of 300 mm Hg is required at the connection point of each
terminal unit with a flow of 40 l/min whilst the system is operating at system
design flow.

9.40 Procedures for these tests are given in Chapter 15.

9.41 A pressure drop of 100 mm Hg (13 kPa) is allowed across the terminal
unit at a flow of 40 l/min (BS 5682:1984). A further pressure drop of
50 mm Hg (7 kPa) is allowed in the distribution pipework, giving a total

95


pressure drop of 150 mm Hg (20 kPa) between the terminal unit connection
point and the plant test point, which should be 450 mm Hg (60 kPa).

Vacuum indicators

9.42 Vacuum indicators should comply with BS 1780:1985 or have an
equivalent performance if electronic indicators are used. Calibration should be
0–760 mm Hg (0–101 kPa). All gauges should be a minimum scale length of
90 mm.

9.43 Vacuum indicators should be located on:

a. the plant control unit indicating the vacuum in the pipeline (ie on the
pipeline side of the bacteria filter);

b. each reservoir.

A differential vacuum indicator should be located across the bacteria filter. All
indicators should be connected directly to the pipework and not isolated by
valves.

Electrical supply

9.44 The electrical supply to the medical vacuum plant should be connected
to the essential electrical supply. A time-delay system should be provided to
avoid overloading the power supply on changeover.

Pump operating and indicating system

General description

functions:


b. individual pump starting;

c. plant status monitoring and indication;

d. alarm signal status unit.

9.46 Provided that the individual pump starters are housed in a separate
compartment, the operating and indicating system may be housed in separate
units or may be installed in a common panel and located on the plant or on
the plantroom wall.

9.47 Pneumatic components should have ventilation. All functions should be
appropriately identified. Indicators should have a design life of at least one
year. The operating system should be capable of automatically restarting after
reinstatement of the power supply.

9.48 The vacuum supply system should be connected to the standby
electrical system. The control system should ensure that pumps restart in
sequence to avoid overloading the essential power supply.

Plant control unit

9.49 The control unit should have a separate power supply for each pump
controlled by a separate sub-circuit. It should be manufactured and installed in

96


accordance with IEE regulations, and the design should be such that no single
component failure in the control unit will result in loss of plant output.

of the pumps or have an automatic sequence selection with a means for
manual override. The control unit should ensure that two or more pumps do
not start simultaneously when power is applied.

9.51 A warning notice which complies with BS 5378: Part 3: 1982 should
be affixed which indicates the presence of low voltage.

9.52 For testing purposes, each pump should have a selector switch which
when turned to the “on” position allows the pump to run continuously.




b. green “pump operating” which indicates that the pump motor is
electrically energised;
c. green “pump operating” which indicates that the pump is drawing
vacuum;

d. an indicator of the vacuum produced in the pipeline.

Pump starter units

9.54 There should be individual starter units, each one operating a single
designated pump. The starters should be provided with safety interlocks as
specified by the pump manufacturers, which should inhibit plant operation
until manually reset by means of a button. The starters should allow
automatic restart after an interruption to the power supply. Each starter unit
should contain the following:

a. an isolator interlocked with the covers;

b. either HRC fuses to BS 88 or suitable circuit breakers to BS EN 60947-2
and/or BS EN 60898;

c. starter;

d. an industrial grade ammeter to BS 89;
e. a total hours counter, if not included in the plant control unit;

f. a green “mains supply on” indicator, if mounted separately from the
plant control unit.

` Plant status monitoring

9.55 A monitoring system must be provided to detect the following faults in
the vacuum supply system:

a. plant faults for each pump:
(ii) motor tripped;
(iii) pump failed to go on load;
(iv) activation of other safety devices supplied by the manufacturers;

97


b. plant emergency – receiver vacuum has fallen, for example, by
50 mm Hg below the cut-in setting for the pump;

c. pressure fault (pipeline) – pipeline vacuum less than 360 mm Hg.


9.56 In addition to the plant control indication there should be a plant status
indicator panel which may be mounted on the plantroom wall or adjacent to
either the pump starter unit or the plant control unit. It should have a warning
notice which complies with BS 5378: Part 3: 1982 to indicate the presence of
low voltage.

9.57 There should be indicators for each pump to show the following
conditions:



c. yellow “motor tripped”;

d. yellow for each individual safety device provided by the manufacturers;

e. yellow “pump failure”.


9.58 The following indication of plant conditions should be provided:

Indication Legend

a. green “normal” indicator normal

b. yellow “plant fault” conditions (b–d), see 9.57

c. yellow “plant emergency” condition (e), see 9.57

d. red “pipeline vacuum fault” plant failure


50 V dc, 50 mA.

system.

9.61 The panel can be incorporated into the plant status indicator unit, or be
a separate unit within a plantroom. If mounted separately, the cabling should
“system fault” lamp should be illuminated on the alarm system status unit,

`Plant management

9.62 Connections should be provided which allow monitoring (but not
control) of plant alarm conditions (b) to (e) and pump running for each
vacuum pump. These connections should be volt-free contacts normally closed
for each condition having a minimum rating of 50 V dc, 50 mA.

98


instructions and be covered by a sound, effective planned preventative

99

10.0 System design – anaesthetic gas scavenging
systems

General

10.1 Anaesthetic gases are considered to be substances hazardous to health
for the purposes of the Control of Substances Hazardous to Health Regulations
1988 (COSHH), except where they are administered to a patient in the course
of medical treatment.

10.2 Detailed guidance on compliance with COSHH is given in EL(96)33 and
enclosure: ‘Advice on the Implementation of the Health & Safety Commission’s
Occupational Exposure Standards for Anaesthetic Agents’, published by the
Department of Health 1996. Further guidance is given in ‘Anaesthetic agents:
Controlling exposure under COSHH’, prepared by the Health Services Advisory
Committee, ISBN 0-7176-1043-8.

10.3 The COSHH regulations set out very specific duties that apply to
anaesthetic gases, and employers have a legal obligation to ensure that these
duties are discharged. It is therefore the responsibility of the general manager
or chief executive to implement the requirements of the COSHH regulations
with respect to anaesthetic gases.

10.4 The anaesthetic gases which are of primary concern are nitrous oxide
and halogenated agents such as halothane, enflurane and isoflurane. These
agents are usually administered in low concentrations compared to nitrous
oxide, and therefore for practical purposes it is only necessary to consider the
effects of nitrous oxide pollution.

10.5 The COSHH regulations require that, for every exposure to substances
hazardous to health, the following should be carried out:

a. assessment of the risk;

b. methods of achieving control of the risk;

c. means of monitoring that the methods of control are maintained in an
effective condition.

10.6 Both publications listed in paragraph 10.2 give details of the
management actions which will need to be carried out in order to comply with
the requirements of the COSHH regulations, and are briefly covered in this
chapter.

10.7 Effective control of exposure to anaesthetic gases will involve a
combination of the following measures:

a. the use of an effective scavenging system to remove the pollution at
source;

b. good room ventilation to dilute pollution from leaks, patients’ expired
air etc;

c. good housekeeping to minimise leakage arising from poorly fitted face
masks, flowmeters inadvertently left on, poorly maintained anaesthetic
or scavenging equipment etc.

100

10.0 System design – anaesthetic gas scavenging systems

10.8 Control of the risk is achieved by a combination of good
housekeeping, that is, minimising leaks, room ventilation and the removal of
waste anaesthetic gases at source by a scavenging system.

10.9 This section covers the specification, design and installation of
anaesthetic gas scavenging systems (AGSS).

Background

10.10 The following anaesthetic gases and agents are typically used in
general anaesthesia:

N2 O 6 litres/min

O2 4 litres/min

}
Halothane

Isoflurane 1–5%

Enflurane

10.11 The flammable anaesthetics such as ether and cyclopropane are no
longer used. Cyclopropane is no longer manufactured. The AGSS is not
usually designed for use with flammable anaesthetic agents. Refer to Health
Guidance Note ‘Static discharges’.

10.12 To ensure that all devices, for example anaesthetic machines,
ventilators and breathing systems, are suitable for the purpose, the guidance
given in BS 5724 Part 1 and BS 5724 Parts 2.12 and 2.13 should be followed.
(See also the ‘Report of a working party to review the anti-static requirements
for anaesthetising areas’.)

10.13 Nitrous oxide and oxygen are usually supplied from the MGPS, but the
halogenated anaesthetic agents are supplied from a vaporiser on the
anaesthetic machine. Leakage and spillage can occur from the anaesthetic
machine, for example when filling vaporisers, or if flowmeters are
inadvertently left switched on.

10.14 There are several different types of breathing circuit which can be used
to administer the anaesthetic gases to the patient, depending on the
procedure to be carried out. Nearly all breathing circuits, apart from paediatric
circuits, incorporate an expiratory valve or port, in the case of a ventilator, to
which a scavenging system can be connected.

10.15 The major source of pollution when a general anaesthetic is
administered is spillage from the expiratory valve or adjustable pressure
limiting valve on the breathing system, or from the expiratory port of the
ventilator. This valve needs to be replaced with a modified valve, to which a
scavenging system can be connected. The characteristics of these valves may
vary with orientation; there may be a further variation when a scavenging
system is connected. The anaesthetist will need to be aware of this and adjust
the valve as appropriate.

10.16 Both the expiratory valve and the expiratory port of the ventilator
should comply with the requirements of BS 6834:1987 (1992), so that a
scavenging system can be connected.

10.17 The expired gas flow depends on whether the patient is breathing
spontaneously or whether a ventilator is being used, and if so, the type of

101


ventilator. Typically the expired gas flow can reach 130 l/min, although this will
be for a short duration.

Sources of pollution and provision of AGS systems

10.18 Sources of pollution include the following:

a. excess gas from the expiratory valve on the breathing system;

b. discharge from the expiratory port of the ventilator, which may include
the driving gas;

c. expired air from the patient;

d. leakage from equipment, poorly-fitted face mask etc;

e. spillage from receiving system of the AGSS;

f. diffusion through tubing (this is thought to be negligible);

g. discharge from gas monitoring equipment (when used).

10.19 An AGSS can remove only pollution which can be captured at source,
that is, it can only remove pollution from the first two and the last sources. It
cannot remove pollution from any other source. Local ventilation systems may
remove pollution discharged into the environment, although the effectiveness
of such systems is being investigated.

10.20 In practice, this means that an AGSS can only be used to remove
pollution from anaesthetic breathing systems incorporating an expiratory valve
or port which complies with the requirements of BS 6834:1987 (1992) to
which an AGSS can be connected.

10.21 Therefore, AGSS should only be installed in areas where anaesthetic
gases are administered as a general anaesthetic via a breathing system. Since
nitrous oxide is almost always administered via a breathing system, an AGS
terminal unit will be required in all areas where a nitrous oxide terminal unit is
provided.

10.22 Details of the level of provision for AGS terminal units are given in
Table 2.

10.23 In general, AGS terminal units should always be provided in areas
where general anaesthetics are administered, such as operating and
anaesthetic rooms. There may be other areas, such as X-ray and endoscopy
departments, where general anaesthetics are also administered on a regular
basis, and therefore consideration should be given to providing an AGS
terminal unit in these areas. This is indicated in Table 2 as a project team
option.

10.24 The Ayres T-piece and Jackson-Rees open-ended reservoir bag are often
used in paediatric anaesthesia. It may not be possible to use an AGSS with
these types of paediatric breathing system. Specially designed local exhaust
ventilation systems have not been shown to be effective, and therefore the
requirement for good room ventilation is particularly important.

10.25 Inhalation analgesia is used for pain relief and reduction of anxiety
during childbirth, dentistry (where the practice is usually referred to as relative
analgesia) and occasionally in physiotherapy, ITU and acute wards, using a
mixture of nitrous oxide and oxygen.

102


10.26 In midwifery, the analgesic is supplied as a mixture of 50% nitrous
oxide/50% oxygen. In relative analgesia, the anaesthetist selects the
composition of the gas by adjusting the mixing valve of the relative analgesia
equipment. In both cases, administration is via a specially designed face mask,
and the patient exhales directly into the environment. Considerable spillage of
nitrous oxide can occur into the surrounding environment.

10.27 It is not possible to use an AGSS when nitrous oxide is
administered in this way as an analgesic.

10.28 For dentistry, local exhaust systems are currently being developed to
remove the pollution from the vicinity of the dental chair where relative
analgesia is used. These may be effective in reducing the resultant
environmental pollution.

10.29 In obstetrics, local exhaust ventilation systems, hoods and other extract
systems have not been shown to be effective in removing the pollution in
delivery areas where 50% nitrous oxide/50% oxygen is used as an analgesic.
In this case, the pollution should be minimised by good room ventilation and
good housekeeping techniques.

10.30 In recovery areas, the major source of pollution is the patient’s expired
gases. Local exhaust systems or proximity devices have not been found to be
effective because of the need for excessively high extract flows and close
positioning of the device to the patient, which may interfere with effective
nursing. In recovery areas, good room ventilation should be provided.

10.31 Health Technical Memorandum 2025 ‘Ventilation in healthcare
premises’ gives further information.

AGSS design

General

10.32 For new installations, an AGSS which complies with the requirements
of BS 6834:1987 (1992) should be installed in all operating departments and
other areas as required, in accordance with the level of provision set out in
Table 2 and as discussed above.

10.33 A typical system schematic is shown in Figure 14. This is taken from
BS 6834:1992 and shows the terminology used. A diagram of a receiving
system is shown in Figure 15.

10.34 For existing installations which do not comply with BS 6834:1987
(1992), an assessment of the effectiveness of the system should be carried out
in accordance with the ‘Operational management’ volume of this HTM. The
assessment should also include tests to ensure that the criteria for patient
safety, as specified in BS 6834:1987 (1992), can be achieved. If these criteria
cannot be achieved, or if the system cannot be shown to be effective in terms
of it ability to remove pollution, then consideration should be given to
installing a system which complies with BS 6834:1987 (1992).

Active and passive systems

10.35 AGSS which comply with BS 6834:1992 are active systems, that is,
the air flow form the disposal system is as a result of a powered device such
as a fan or suction unit.

103


Figure 14 Schematic diagram of AGSS to BS 6834

104


Figure 15 Schematic diagram of receiving system (reproduced by kind permission of MEC Ltd)

105


10.36 Passive systems are those in which the air flow from the disposal
system does not result from a powered device. The patient provides the driving
force to expel the gases.

10.37 Passive systems are not recommended. This is because they cannot
meet the specified safety requirements under all conditions due, for example,
to variations in wind direction and pressure which may result in excessive
suction pressure.

10.38 Some AGSS have been installed in which the disposal system discharges
into the mechanical ventilation system; such systems may be described as
semi-passive or assisted-passive systems. The ventilation system provides
the motive force to remove the pollution. These systems are not
recommended because, like passive systems, their performance is not reliable
and they cannot meet specified safety requirements under all conditions.

10.39 Where passive and assisted-passive systems are installed, an assessment
of their efficiency should be carried out as described in the ‘Operational
management’ volume of this HTM. Consideration should be given to replacing
these systems with an AGSS which complies with
BS 6834:1992.

General design requirements

10.40 The medical vacuum system should not be used to remove waste
anaesthetic gases. The medical vacuum system is designed to provide a suction
pressure of 400 mm Hg (53 kPa) at the terminal unit – see Chapter 9. If the
patient was inadvertently connected to this suction pressure, it would almost
certainly prove fatal.

10.41 Canisters which adsorb the volatile agent from the waste anaesthetic
gases are available, but are not recommended as a substitute for an AGSS
because they cannot adsorb nitrous oxide.

10.42 All safety devices should fail safe.

10.43 AGSS are in contact with the patient’s expired breath and hence there
is the potential for bacteriological contamination. The materials should be
reasonably resistant to corrosion, and should withstand cleaning, disinfection
or sterilization as appropriate. It is recommended that the transfer system and
other detachable components should withstand steam sterilization at 134 +
3–0°C. The manufacturer should recommend methods of cleaning, disinfecting
and sterilizing the system and the manufacturer’s recommendations should be
followed.

10.44 The fixed pipework may be of copper or other suitable material such as
PVC. Where copper pipework is installed at the same time as the MGPS, it is
desirable to use degreased pipework to the same specification as that used for
the MGPS (see Chapter 13) in order to avoid confusion.

10.45 Where PVC pipes larger than 38 mm diameter pass through a fire
compartment, they should be protected with metal sleeves extending for 1 m
either side of the compartment, in accordance with the building regulations.
The requirements of Firecode and HTM 81 should be followed.

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Safety criteria

10.46 The following safety criteria are specified in BS6834:1987 (1992) and
all AGSS should comply with these criteria, irrespective of whether they
comply fully with the other requirements of the British Standard.

Table 15 Safety criteria for AGSS

Maximum pressure Maximum pressure
at inlet at 30 l/min at inlet at 90 l/min
continuous flow continuous flow

Positive pressure relief at 50 Pa 500 Pa
inlet to transfer system

Maximum pressure Maximum pressure
increase at inlet at increase at inlet at
30 l/min for 5 s 90 l/min for 5 s

With any hose or tubing 1 kPa 2 kPa
totally obstructed

Maximum induced flow to the receiving system from the transfer system

0.5 l/min

10.47 Experience shows that any sub-atmospheric pressure at the patient end
of the AGSS may induce a gas flow from the breathing system under certain
conditions. Whilst this does not result in any barotrauma, there have been
instances where insufficient gas has been available to the patient as a result of
this phenomenon. Therefore there is a requirement in the British Standard
that the induced flow from the patient’s breathing system should not exceed
0.5 l/min.

Performance criteria

10.48 An AGSS which complies with BS 6834:1992 is intended to remove all
gases delivered to the receiving system, within the performance and safety
criteria specified. There should be no spillage of nitrous oxide from the
receiving system when the AGSS is set up as specified in the British Standard.
This test is intended to be carried out by the manufacturer. It is not easy to
reproduce the specified challenge waveform in an operating department. It
should not be necessary to carry out this test on-site, as no spillage should
occur provided the extract flow and pressure losses are within the specified
limits.

10.49 The performance criteria for the disposal system are specified in the
British Standard in terms of the extract flows at specified resistance, as shown
in Table 15.

10.50 The performance criteria shown in Table 2. (Anaesthetic gas
scavenging systems) should be achieved regardless of the number of terminal
units on each system; where more than one terminal unit is provided on the
system, the performance criteria should be achieved with all, or one, of the
terminal units operative.

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Table 16 Performance criteria for disposal systems

Flow with a resistance to flow Flow with a resistance to flow
producing a pressure drop of 1 kPa producing a pressure drop of 4 kPa

Maximum flow 130 l/min Minimum flow 80 l/min

Flow diversity

10.51 Although more than one AGS terminal unit may be installed in an
operating room or anaesthetic room for convenience, it may be assumed that
only one terminal unit will be in use at any given time. It may also be assumed
that the AGS terminal unit in the anaesthetic room and in the operating room
will not be in use simultaneously. Therefore, when sizing the plant, assume
one receiving system only in use for each theatre suite.

Discharge outlet

10.52 Careful consideration should be given to siting the discharge outlet
from the disposal system. It should preferably be sited at roof level, well away
from ventilation inlets, opening windows and other apertures, to prevent
pollution from re-entering the building.

Duplex system

10.53 Where duplex systems are installed, each pump should be capable of
meeting the full design flow.



Indication Legend

a. green “mains on and
air flow” normal
b. yellow “duty pump failed” plant fault

c. red “system failed” plant emergency

10.55 Indicator panels should be installed in the operating room and the
nurses’ station.

10.56 The air flow, that is, “plant on”, indication should be initiated by either
a pressure switch or air flow detection device at the pump, that is, mains
supply to the pump is not sufficient.

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11.0 System design – nitric oxide

Nitric oxide pipeline installations

Introduction

11.1 Nitric oxide (NO) pipeline installations are a developing science at
preliminary stages. The following paragraphs are intended as best practice
guidance at present.

11.2 The use of nitric oxide as a selective pulmonary vasodilator has had a
major impact on the management of both neonates and adults suffering from
respiratory distress syndrome. The immediate improvement in the patient’s
condition with nitric oxide has made its use routine, although the long-term
benefits have yet to be established by clinical trials.

11.3 Until recently, delivery systems have relied on the use of portable
cylinders, either AV (10 litre) or AK (40 litre) aluminium cylinders located at
the bedside. The introduction of such cylinders, however, adds to the
congestion in highly serviced ward spaces and proves an additional safety
hazard to both staff and patients. Whereas the smaller AV-size cylinder is
more manageable, its smaller capacity exacerbates the likelihood of running
out, which could cause patients to suffer pulmonary vasodilation resulting in
hypoxia and pulmonary hypertension.

11.4 The installation of a pipeline distribution system is intended to provide
a safe and reliable method of gas delivery. It also helps to reduce congestion
in the bed area and to ensure an adequate continuous supply of gas without
compromising its quality.

Design considerations

11.5 In the UK, nitric oxide for medicinal use is currently supplied as a
mixture of 1000 vpm in nitrogen. (This may change in the future.)

The breathing system should include 11.6 The therapeutic concentration of nitric oxide required in the patient
nitric oxide and nitrogen dioxide breathing system is normally between 5 and 20 vpm, with a maximum flow at
monitoring systems each terminal unit of about 200 ml/min. The gas is administered in
conjunction with medical oxygen to maintain the appropriate oxygen
concentration to the patient.

11.7 In the presence of oxygen, nitric oxide forms higher oxides of nitrogen,
particularly nitrogen dioxide (NO2), and dinitrogen trioxide (N2O3). The rate of
conversion depends upon both the concentration of nitric oxide and oxygen.
The higher the concentration of both components, the faster the rate of
oxidation. This is shown in Table 17.

11.8 In the presence of moisture, these compounds form nitric acid (HNO3)
and nitrous acid (HNO2) which will react with the traditional materials used for
MGPS.

11.9 Although during normal operation no part of the pipeline should
become contaminated with oxygen and moisture, experience has shown that

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such contamination is possible. Consequently, the use of austenitic 303
stainless steel is recommended for terminal units, non-interchangeable screw
thread (NIST) connectors, pipeline installation components and manifolds.
Elastomeric components used for valve seats, low-pressure flexible connecting
assemblies etc should be compatible with nitric oxide.

Table 17 Nitric oxide conversion rates

NO ppm

O2% 20 40 80 120

20 60.08 12.86 3.00 1.32
30 40.05 8.56 2.00 0.88
40 30.03 6.43 1.35 0.66
50 24.03 5.15 1.20 0.52
60 20.01 4.28 1.00 0.44
70 17.16 3.66 0.85 0.37
80 15.09 3.20 0.75 0.33
90 13.35 2.85 0.66 0.24
100 12.01 2.56 0.60 0.26

Time (min) to yield 5 ppm NO2 with different mixtures of NO in nitrogen.

Provision of terminal units, valves and area valve service units (AVSU)s

11.10 In highly serviced ward areas such as neonatal intensive care units and
ITUs, it is normal policy to provide at least two oxygen, two MA(4 bar), and
two vacuum terminal units for each bed space.

11.11 To ensure maximum flexibility it is similarly recommended that two
nitric oxide terminal units are installed for each bed space.

11.12 The provision of nitric oxide has also been suggested for installation in
specialist operating departments. A clinical judgement will have to be made on
such provision, taking into account the additional complexity and
consequences of discontinuation of the supply during patient transfer.

11.13 BS 5682 does not include a terminal unit for nitric oxide. In the absence
of standards the dimensions given in Table 3 are recommended; they are
based on the figures and tables in BS 5682:1984.

Manifold

11.14 The manifold should be located near to the areas to be served, in
secure accommodation and provided with good ventilation to the outside. The
accommodation should comply with the general requirements in this HTM and
have good access for cylinder handling.

11.15 In existing premises it may not be practicable to provide an external
manifold room. In such cases, mechanical ventilation will be necessary to
prevent the accumulation of gas in the event of a leak and during purging
after cylinder changing.

11.16 The manifold should be semi-automatic, complying with the
requirements for medical gas manifolds in this HTM.

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11.17 Additionally, the manifold should have a nitrogen purging facility to
purge any air introduced during cylinder changeover on each tailpipe. The
purging system should be provided with venting to outside to allow purging
with the working gas before the manifold is made ready for service. The
pressure of the nitrogen supply used for purging needs to be set below the
minimum operating pressure of the manifold, to prevent supply of nitrogen to
the patient and to prevent overriding of the alarm system.

11.18 Purging/changeover procedures are given in the ‘Operational
management’ volume of this HTM.

11.19 The manifold and line pressure safety valve vents should be piped to
discharge in a safe external location.

11.20 A gas-specific connector for nitric oxide cylinders is currently under
review. This connector will include a minimum pressure retention device to
prevent cylinder contamination with air.

11.21 The manifold operating pressure should be set to 4.2 bar g as
recommended for other medical gases. The nitrogen purging system should
be set to operate at 2 bar g, such that the warning system will continue to
alarm if the service gas cylinder valves are not opened after cylinder charging.

Provision of valves

11.22 Where nitric oxide systems are installed within or close to the
department served, the control of the distribution system will be by AVSUs
and valves installed as part of the manifold system.

11.23 Where nitric oxide manifolds are remotely located, AVSUs will need to
be installed within the ward area.

Provision of AVSUs

11.24 AVSUs should be provided for the neonatal intensive care unit, ITU and
theatres (if provided) to control one of each pair of terminal units installed.
This will ensure continuity of gas supply if the need arises for urgent servicing
or repair of terminal units.

11.25 AVSUs for nitric oxide systems will not require NIST connectors or
blanking spades. They will be of stainless steel construction and enclosed in a
lockable box with emergency access.

11.26 Many nitric oxide systems will be installed in existing premises which
may preclude the recommended valving arrangement. Where it is
impracticable to separate individual pairs of terminal units, it is recommended
that at least half of the total number should be serviced from a separate
AVSU.

11.27 AVSUs will be required to isolate terminal units for servicing, since
nitric oxide and nitrogen dioxide are toxic, and the check valves typically
included in terminal units for this purpose are not considered to be sufficiently
gas-tight.

Pipeline distribution

11.28 The flows of nitric oxide in clinical use are modest and pressure loss is
not a critical design factor. The installation will generally comprise 6 mm
stainless steel tubing installed by means of orbital welding using an argon

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shield. Argon should also be used during pressure testing and purging prior to
commissioning.

Identification

11.29 The pipeline installation should bear identification generally in
accordance with this HTM. Green has now been accepted as the identification
colour.

Alarm systems

11.30 The main alarm system indicator panel should be located in one of the
critical care areas where, as stated in the operational policy for the hospital,
staff responsible for cylinder management can be contacted. Repeater alarm
panel(s) should be located elsewhere, for example the neonatal intensive care
unit.

11.31 The alarm system should comply fully with the appropriate
requirements for manifold alarms and as follows:

Condition Legend Colour Audible

a. duty bank change cylinder yellow yes
empty –
change over
to standby bank

b. standby bank change cylinder yellow yes
below 50% immediately
capacity

c. purge cylinder change cylinder yellow yes
pressure low immediately *
10%

d. pipeline pressure pressure fault red yes
below 80%

* This action will be necessary before changing working gas cylinder.

Nitric oxide – risk assessment for COSHH compliance

11.32 Concerns about the effects of exposure to waste anaesthetic agents are
well documented and have lead to the development of AGSS. In some
departments, AGSS is not a practical control method and, based on a risk
assessment, ventilation is considered to be a satisfactory alternative.

11.33 The quoted occupational exposure limits for nitric oxide are 25 ppm
over an 8 hour time-weighted average and 35 ppm for 15 minutes, and for
nitrogen dioxide are 3 ppm over an 8 hour time-weighted average and 5 ppm
for 15 minutes.

11.34 Therapeutic concentrations of nitric oxide are extremely low, below
current occupational exposure limits. The conversion to higher oxides of
nitrogen (which is time- and concentration-dependent) is unlikely to result in
occupational exposure limits being exceeded.

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11.35 Tests have shown that with no scavenging, but ventilation providing
12 air changes per hour, the highest levels recorded were in the vicinity of the
ventilator outlet and were between 2.0 and 8 ppm nitric oxide and 0.2 to
0.5 ppm nitrogen dioxide were recorded. (With scavenging, the maximum
levels were respectively 0.2 ppm and a nil value for nitrogen dioxide.)

11.36 On this evidence, the provision of waste gas scavenging does not
appear to be an occupational hygiene priority although, if otherwise available,
staff may wish to use an existing system. (Standard AGSS components and
materials are satisfactory.)

11.37 Chemical adsorbsion filters are possible, but their availability is limited
and, taking into account the relative risk, may introduce a greater problem of
disposal.

Validation and verification

11.38 Pressure testing and purging should be carried out in accordance with
‘Validation and verification’, except that argon should be used prior to this
stage.

11.39 On satisfactory completion of all purging, the system should be filled
with the working gas and all terminal units should be checked for gas
identity. Quality tests should be performed using argon prior to this stage.

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12.0 Warning and alarm systems

General

12.1 The provision of a warning and alarm system is essential to monitor the
safe and efficient operation of MGPS. There are three reasons for this
monitoring:

a. to indicate normal function of the pipeline system by means of visual
indicators;

b. to warn by visual and audible indication that routine replacement of
cylinders or other engineering action is required;

c. to inform the user by visual and audible emergency alarms that
abnormal conditions have occurred which may require urgent action by
the user. This alarm condition will require a rapid response by the
various departments’ staff.

12.2 A schematic diagram of a typical warning and alarm system layout is
shown in Figures 16 and 17.

12.3 Warning and alarm systems are required for all medical gas and
vacuum systems. A much simplified system is required for surgical air systems
and for anaesthetic gas scavenging systems (AGSS), with the
warning/indication panel located in the operating room.

12.4 Warning and alarm systems comprise pressure sensors, a central system
providing information on all monitored functions, with repeater panels located
where information is required to ensure the necessary action is taken. Area
alarms should be provided to give warning to users downstream of the
designated area valve service unit (AVSU).

12.5 Pressure sensors should be connected to the pipeline by means of
minimum leak devices.

12.6 All MGPS warning and alarm indicating panels should comply with the
requirements of this HTM, including all operating room panels.

Panel location

Central indicator panel

12.7 Warning and alarm conditions for all medical gases in a central system
should be displayed on a central panel which is located in a position subject to
continuous 24 hour observation, such as the telephone switchboard room or
the porter’s lodge.

Repeater indicator panel location

12.8 Repeater panels include an audible facility and should be provided for a
central system to display information which is essential for the continuing
operation of the system.

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Figure 16 Typical warning and alarm system layout (reproduced by kind permission of Shire Controls)

115


Figure 17 Typical area alarm panel (reproduced by kind permission of Shire Controls)

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Area warning and alarm panel location

Sensors may be fitted within the 12.9 Local systems to display high and low gas pressure in the area should
AVSU enclosure be installed downstream of the AVSU. The sensors for these systems should
be located downstream of designated AVSUs. It should not be possible to
isolate the sensor with a separate shut-off valve. The panel, appropriately
labelled, should be located at a nurses’ station within each department, and
in special departments (SCBU, ITU and A & E). Some warning system
information may be appropriate in the pharmacy department, particularly in
the case of pressure swing adsorber (PSA) plant, synthetic air plant and
compressed air systems.

System description

System components

12.10 Warning and alarm systems include the following functional elements:

a. transmitters which convert the signal from the plant or manifold volt-
free alarm contacts into a form which can be transmitted via
multiplexed cable (for example using pulse width modulation – see
Figure 18). The transmitter may be a separate unit or may be
incorporated:
(i) in plant or manifold control panel;
(ii) in a separate unit;
(iii) in an indicator panel.

Cases (ii) and (iii) should include line fault monitoring devices;

b. indicator panels which display the transmitted signals;

c. interconnecting multiplex wiring which connects all transmitters to all
indicator panels.

System layout

Central system

12.11 A typical system layout is shown in Figure 16, which shows initiating
devices at remote locations such as the vacuum insulated evaporator (VIE)
compound, medical air and vacuum plantrooms, nitrous oxide manifold room
and emergency/reserve manifold rooms. The transmitters are normally located
close to the initiating devices. Indicator panels are typically located at the
telephone exchange, the porter’s room and the engineer’s office, to provide
information requiring action by engineering and other support staff. Certain
critical care areas such as theatres, delivery suites, special care baby units and
intensive care units should also have repeater indicator panels on the central
system to show emergency alarms which require action from the user.

Area warning and alarm systems

12.12 A typical layout of an area system is shown in Figure 17. For each gas
service there should be local pressure switches for high and low pressure.
These conditions should be indicated on a locally mounted indicator panel,
with facility to provide a common alarm condition for connection to other
alarm panels. The extent of the interconnecting wiring in an area alarm
system

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To alarm system

Figure 18 Signal path for typical plant (reproduced by kind permission of Shire Controls)

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is reduced by comparison with a central system. The area alarm panels carry
no indication of the warnings for cylinder replacement and plant function
which are given on central systems.

General requirements

Labelling

12.13 All visual signal panels should be permanently labelled according to
their function. including clear identification of the areas, rooms or
departments served.

Visual signals

12.14 Flashing visual signals should have alternate periods on and off, each
of equal duration between 0.25 and 0.50 seconds.

12.15 There should be two separately energised light sources for each signal,
arranged so that the failure of one source does not affect the other.

12.16 The light sources should have a design life of at least five years of
continuous operation.

Audible signals

12.17 All audible signal tones should be modulated equally at a rate of 4
Hz±10% between two tones of 440 Hz±10% and 880 Hz±10%.

Automatic re-setting

12.18 When a warning or alarm signal occurs and the system condition
subsequently reverts to normal, the corresponding visual and audible signals
should automatically reset to normal.

Temporary muting

12.19 Means must be provided on each panel for the user to mute the
audible signal. The signal must re-sound after a nominal 15-minute period if
the fault condition still exists. The process of muting and reinstatement of the
signal should be repeated until the fault condition has been rectified.
Operation of the mute should be accompanied by change from flashing to
steady illumination of the corresponding visual indicator on the central panel
only. Operation of the mute on area alarm or repeater panels should not be
accompanied by a change from flashing to steady illumination.

Continuous muting

12.20 An internally mounted switch should be provided to allow continuous
muting during periods of maintenance. When the system condition returns to
normal the continuous muting should automatically reset to normal operation.
When the continuous muting is in operation on any alarm condition, it should
not prevent the operation of the audible signal on other alarm conditions
when a fault condition arises.

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Electrical wiring

12.21 All electrical wiring should be in accordance with IEE regulations.

System integrity

12.22 If extra low voltage (ELV), maximum 50 V, is superimposed on the
signal or communication circuit (for example by cross-connection), the system
design should ensure that any damage to the system is limited to replaceable
panel components and that such damage is indicated as a system fault.

12.23 The performance of the system should not be compromised by the use
of multi-core cabling which carries ELV and communication signals in adjacent
cores.

12.24 The system should be designed to reject spurious radio frequency (RF)
or mains noise typically arising in hospitals, examples being diathermy
equipment and current spikes caused by plant start-up etc.

Relay conditions

12.25 If relays are used to transmit alarm signals, the relays should be
energised in their normal closed condition.

Mains power supply

12.26 The mains electricity supply should be derived from the essential power
supply (that is, must be on the emergency system).

SELV/FELV power supply

12.27 The panel power may be designed either as a safety extra low voltage
(SELV) system or a functional extra low voltage (FELV) system, as defined in
Part 4 of the IEE Wiring Regulations.

12.28 The ELV power supply may be housed either in the alarm panels or in a
separate metal enclosure.

12.29 The power supply should be rated for the full load of the panel, with
visual and auditory signals on all normal and alarm conditions.

Test facility

12.20 Each panel should be provided with a means to test all visual and
audible signals on that panel. The power supply should be capable of
sustaining all indicators and audibles.

Warning and alarm system faults

General

12.31 A flashing red visual indicator and an audible signal should operate on
all panels when any of the following conditions occur:

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a. line fault from the initiating device;

b. communication fault or other wiring fault;

c. mains power failure.

Line fault

12.32 The system should monitor the integrity of the lines between the
initiating devices and the panel or transmitter units. The “alarm system fault”
condition should be indicated on loss of integrity, for example open or short
circuits.

Communication/wiring fault

12.33 The system should indicate an alarm system fault in the event of loss
of data transmission between panels and transmitters.

Mains power failure

12.34 Failure of mains power should be shown by a flashing red indicator
and an audible signal, which should be powered from an internal battery.
The audible signal may be muted and not automatically reinstate as required
under normal power supply (see paragraph 12.19), but the visual indicator
should continue to flash until either the fault has been rectified or the battery
has discharged.

Standby battery

12.35 A battery should be provided with sufficient capacity to power the
visual and audible “alarm system fault” signal for a minimum period of four
hours. The battery should be sealed and exchangeable and should
automatically recharge within 72 hours.

Legend

12.36 The legend on this indicator should be “alarm system fault”.

Indicator panel requirements for all systems

Indicators

12.37 Panels should be provided with all indicators for the gas services in
local use.

12.38 The visual indicators should be arranged vertically in priority order,
with the normal indicators at the top. The sequence of gas services should be
from left to right:

a. medical oxygen (cryogenic and cylinders/pressure swing adsorber (PSA)
systems);

b. nitrous oxide;

c. nitrous oxide/oxygen mixture;

d. medical air 400 kPa (compressor plant,cylinders and synthetic air);

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e. medical vacuum (pumps);

f. nitric oxide;

g. oxygen/carbon dioxide mixture;

h. surgical air 700 kPa.

12.39 In addition to the gas service signal indicators, each panel must include:

a. a green “power on” indicator without an audible signal;

b. a red “alarm system fault” indicator with an audible signal.

Labelling

12.40 Panels should be labelled as follows:

a. medical gas alarm;

b. with the identification of the medical gas services indicated, and the
areas and departments served.

Construction

12.41 The fascia panel should be removable to allow access to the rear of the
fascia or to the panel for maintenance purposes.

12.42 Access to the interior of the panel should be tamper-proof.

12.43 It should be possible to replace the source of illumination without
removing the legend.

12.44 Panels should have electrical sections with protection at least equal to
IP 32 of BS 5490:1977.

12.45 Panels and their housings should be of adequate strength for their
purposes and be manufactured from corrosion-resistant materials.

12.46 If gas services are brought into the panel, they should be housed in
separate, enclosed compartments which are vented to the outside.

12.47 There should be gas-tight seals where electrical services pass through
any gas compartment.

Remote audible sounder

12.48 All panels should have provision for connection to a remote audible
sounder.

Central indicator panel requirements

Displays

12.49 The central panel should display all signals for all MGPS which are
generated by the warning and alarm system, as follows:

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Normal

The normal condition for all piped MGPS should be displayed as a
steady green visual signal. The “normal” indicator should extinguish in
warning and alarm conditions.

Warnings

Warning conditions appropriate to each MGPS should be displayed as a
flashing yellow visual signal which may be accompanied by a mutable
audible signal (see Table 19).

Emergency alarms

Emergency alarms are generated by loss of pipeline pressure or vacuum
and are indicated by flashing red visual signals accompanied by mutable
audible signals.

Alarm system fault

The “alarm system fault” condition should be displayed as a flashing
red visual signal accompanied by a mutable audible signal.

Mute functions

12.50 The temporary mute should cancel the audible signal for about 15
minutes and change the visual indicators from flashing to continuous on all
central and repeater panels.

12.51 Operation of the continuous mute should inhibit the 15 minute
reinstatement of the audible alarm.

12.52 Operation of the mute should not inhibit the visual or audible
indication of any subsequent alarm conditions.

Panel legend and display

12.53 Panel legend and display should be as shown in Table 19.

Repeater indicator panel requirements

Displays

12.54 The repeater indicator panel should always display “normal”,
“emergency alarm” and “alarm system fault” conditions as given above. The
repeater panel should display some or all of the warning conditions which are
displayed on the central indicator panel as given in paragraph 12.49. The
extent of the display of warnings should be varied to suit local clinical
requirements.

Mute functions

12.55 The temporary mute should cancel the audible signal for about
15 minutes whilst the visual indicator continues to flash. Operation of the
temporary mute (on the central panel) should change the visual indicator to
continuous illumination.

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12.56 Operation of the continuous mute must inhibit the 15-minute
reinstatement of the audible alarm.



12.58 The panel legend and display should be as shown in Table 19.

Area warning and alarm panel

Displays

12.59 Area panels should display “normal”, “emergency alarm” and “alarm
system fault” conditions as given in paragraph 12.49.

Mute functions

12.60 The temporary mute should cancel the audible signal for about 15
minutes whilst the visual indicator continues to flash.



12.62 The panel legend and display should be as shown in Table 20.

Location

12.63 The initiating devices for local area alarms should be located after
designated AVSUs. This designated position will normally be after the final
AVSU.

12.64 The area alarm panel should be located where it will be clearly visible,
for example in the operating room or at the reception desk, not in a corridor
or unmanned area.

12.65 Area alarm panels should be designed similarly to central alarm panels.
All alarm/indicators installed in operating departments should comply with the
requirements of this HTM, and any medical gas indicator should similarly
comply with these requirements.

12.66 For multi-theatre complexes, and critical care areas with several AVSUs,
the signals from each theatre area alarm panel may be multiplexed to a single
alarm panel.

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Table 19 Signals and display locations on central alarm systems

Plant Alarm condition Legend Colour Auditory signal Location ABCD

Cryogenic oxygen plants 1 VIE low <50% Refill liquid Yellow yes AB
2 VIE low <25% Refill liquid immediately Yellow yes AB

Automatic manifolds 1 duty bank empty; standby Change cylinders
bank running
2 standby bank below Change cylinders Yellow yes ABD
10% capacity (14 bar N2O) immediately Yellow yes ABCD

Medical air compressor 1 Plant fault Plant fault Yellow yes AB
2 Plant emergency Plant emergency Yellow yes ABC

Surgical air supply 1 System fault Change cylinders/ Yellow yes AD
plant fault
2 Emergency/reserve low Reserve bank empty/ Red yes AD
(if installed) plant emergency

Medical vacuum plant 1 Plant fault Plant fault Yellow yes AB

Oxygen concentrator 1 Plant fault Plant fault Yellow yes AB

Compressed cylinders on Reserve pressure below Reserve low Yellow no AB
reserve manifold serving an 68 bar (<14 bar for N2O)
automatic manifold

Compressed air cylinders on Pressure in either bank of Reserve low Yellow no ABC
reserve manifold serving a reserve <50%
cryogenic oxygen system

Compressed cylinders on Pressure in either bank of Reserve low Yellow no ABC
reserve manifold serving a reserve < 50%
compressor plant

Pressure fault (pipeline) For each gas service to indicate Pressure fault Red yes ABC
High or low that the pressure in the
distribution system has
risen/fallen 20% from normal
working pressure

Vacuum pressure (pipeline) To indicate that the vacuum in Pressure fault Red yes ABC
the pipeline serving the
department has fallen 20%
below the normal working
vacuum

Locations:
A central panel – telephone operator/switchboard and or/porter’s room/24-hour manned;
B facilities management office;
C theatre manager’s desk, special care baby unit and ITU nurses’ station;
D operating room.
For nitric oxide manifold alarm systems refer to Chapter 11.

Table 20 Area alarm legend and display

Alarm function Legend Colour Auditory signal

For each gas service to indicate that the pressure in the pipeline serving the department has high red yes
risen 20% above normal working pressure pressure

For each gas service to indicate that the pressure in the pipeline serving the department has low red yes
fallen 20% below normal working pressure pressure

For vacuum to indicate that the vacuum in the pipeline serving the department has fallen low red yes
20% below normal working vacuum vacuum

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13.0 Pipeline installation

Accommodation of pipes

13.1 Generally, MGPS should be kept away from areas where they may be
subject to any of the following:

a. mechanical damage;

b. chemical damage;

c. excessive heat;

d. splashing, dripping or permanent contact with oil, grease or
bituminous compounds, electrical sparks etc.

13.2 Service ducts or voids containing medical gas pipelines should have
adequate ventilation to prevent gas concentrations in the event of any leakage
occurring.

13.3 Exposed pipelines should not be installed in lift shafts, kitchens,
laundries, boiler houses, generator rooms, incinerator rooms, storage rooms
designed to house combustible materials or in any other fire risk area. Where
pipelines in hazardous areas are unavoidable, they should be enclosed in
non-combustible materials that will prevent the possibility of the liberation of
gases into the room in the event of pipeline failure.

13.4 Where pipelines are run in enclosed ducts with other services such as
steam mains and water supply systems, they should be inspected regularly as
corrosion can occur as a result of chloride deposits following leakage. They
should not be run in enclosed ducts with other services where they cannot be
inspected.

13.5 Pipelines should be protected from the possibility of lightning strikes.

13.6 Pipelines should be suitably protected where there is a possibility of
physical damage, for example from the passage of trolleys. Wherever
practicable a clearance of at least 25 mm should be maintained between each
service and 150 mm should be the separation distance between medical gas
pipeline and heating, hot water service and steam pipelines. Where pipelines
cross over other services and a clearance of 25 mm cannot be maintained, they
should be electrically bonded and wrap insulated, in accordance with IEE
regulations. They should be bonded to main earth at building entry and exit.

13.7 Buried pipelines should be run in a trench not less than 450 mm x
450 mm, with the pipe protected throughout its length by a continuous glazed
earthenware pipe or carried in properly drained ducts with removable covers.
These glazed pipes or ducts should be further protected where the pipe
crosses areas used by wheeled traffic; in such areas the glazed pipes and ducts
should be encased in concrete. Multi-way ducts should be used where more
than one pipe is to be carried.

13.8 The route of the pipeline should be identified on the surface and
should be clearly shown on site layout drawings. Pipelines concealed within
walls and floors should have their route clearly shown on “as-fitted” drawings.
Pipelines should not be encapsulated in floors, and any joints should be kept to
the minimum practicable. Pipelines in stud or plasterboard walls or partitions
are acceptable.
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13.9 Care is required when selecting pipeline routes to prevent the pipes
coming into contact with electric cables and wiring, and to minimise the risk
of electric shock in the event of a fault on adjacent cables. See Chapter 2.

Pipeline materials

Quality

13.10 The manufacturer should comply with BS EN IS0 9000 for pipes and
for all materials including fittings, terminal units etc. A complete specification
is given in Model Engineering Specification C11.

13.11 Where materials are obtained from suppliers from other countries, the
suppliers should be registered in accordance with BS EN IS0 9000.

Pipes

13.12 Material for pipes should be phosphorus de-oxidised, non-arsenical
copper to BS 6017. Dimensions must be in accordance with BS 2871, Part 1,
Table X or Table Y.

Pipe jointing fittings

For straight couplings, expanded joints 13.13 Materials for pipe jointing fittings must be phosphorus de-oxidised,
may be made instead of using BS 864 non-arsenical copper to BS 6017:1981 (1989). Pipe jointing fittings should be
fittings end-feed capillary fittings to BS 864.

Other fittings

13.14 Other fittings for connection to copper pipes, for example valve and
control panel fittings, may be of copper, brass, gunmetal or bronze to the
appropriate standard.

Cleaning

Pipes

Pipes should only be cut with wheel 13.15 All pipes must be cleaned and degreased for oxygen service and be
pipe-cutters, not hacksaws, to prevent free of particulate matter and toxic residues. They must be individually capped
the ingress of particulate matter at both ends and delivered to site identified as medical gas pipes.

Pipe jointing fittings

13.16 All pipe jointing fittings and sub-assemblies of fittings for connection
to pipes must be cleaned and degreased for oxygen service and be free of
particulate matter and toxic residues. They must be individually sealed in bags
or boxes and delivered to site identified as medical gas fittings.

13.17 Although it is not essential to degrease vacuum installations, these are
frequently installed by the contractor simultaneously with the medical gas
pipelines. Degreased pipe and fittings should, therefore, be used for the

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vacuum installations to avoid confusion. PVC pipework may also be used for
vacuum and anaesthetic gas scavenging systems (AGSS), and is generally used
for larger systems.

Pipeline jointing

General

13.18 Except for mechanical joints, copper-to-copper joints only will be
permitted on site, made with brazing filler rods which can be used without flux
and in the presence of oxygen-free nitrogen, which will be blown through the
pipeline during brazing procedure to prevent the formation of oxides.

13.19 Carbon dioxide should not be used as the inert gas shield.

13.20 This method eliminates the formation of oxide within the pipe, leaving
a clean bore. Some slight burnishing may occasionally be observed on
sectioned joints. Purging is still required to remove the internal shield gas and
the other particulate matter not associated with the brazing operation.

13.21 Copper joints to brass or gunmetal fittings will require the use of flux,
with subsequent cleaning to remove the flux residues and oxide deposits.

13.22 Heating of the joint for brazing should be carried out with
oxygen/acetylene or acetylene, hydrogen, liquid petroleum gas/ambient air
torches. Additional heating may be required for some fittings, for example by
means of a second torch.

13.23 In order to maintain the pipeline cleanliness and prevent formation of
verdigris after completion, it will be necessary to maintain the completed
system charged with medical air until the installation is finally commissioned.
On larger projects completed sections of pipeline should be similarly protected.

13.24 The techniques recommended cover all copper-to-copper joints and all
copper-to-brass/gunmetal/bronze joints in an MGPS, and are explained in more
detail below.

13.25 By agreement between the health facility management and the pipeline
contractor, the use of a purge gas may be waived on joints such as break-ins
to old pipeline systems, where pipe joints will not have been made in
accordance with this new technique.

13.26 This new technique should be used on all medical gas pipeline services.
The method is recommended for use in other non-clinical departments in
hospitals, such as pathology laboratories.

Jointing methods

13.27 Mechanical (threaded or flanged) joints may be made where A procedure for the removal of flux
pipelines are connected to items such as valves and control equipment. For residues and copper oxides is given in
vacuum pipelines of 76 mm diameter and above, screwed or flanged paragraph 13.40. Any alternative
compression fittings may be used. Mechanical joints should not be used process which is equally effective may,
elsewhere for general pipework installation. however, be substituted

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Where brass/gunmetal/bronze fittings 13.28 Brazing copper to brass/gunmetal/bronze
form part of an installation, they
a. brazed joints should be made using a copper-silver-zinc brazing alloy to
should be supplied to site individually
BS 1845 and an appropriate flux;
packed and complete with copper
pipe tails brazed to them so that these b. the flux residues and copper oxides created by this process should be
fittings can be joined to the pipeline chemically removed and if necessary the complete assembly must be
installation by fluxless brazing. cleaned and degreased for oxygen service;
Because of this requirement, it will be
c. no flux should be used for making joints on site. Joints must be carried
necessary for a copper-to-copper
out under controlled conditions off-site and sub-assemblies delivered to
brazed joint to be made adjacent to
site.
these fittings, for example in a wall
adjacent to a terminal unit or a valve
13.29 Brazing copper-to-copper joints:

a. brazed joints should be made using a silver-copper-phosphorus brazing
alloy to BS 1845. No flux should be used;

b. brazing should be carried out using oxygen-free nitrogen as an internal
inert gas shield, to prevent the formation of oxides on the inside of the
pipes and fittings;

c. when brazing, ensure adequate protection of adjacent pipe runs to
avoid oxidation.

Pipe preparation

13.30 Pipe ends should be cut square with the pipe axis, using sharp wheel-
cutters and cleaned of any cuttings or loose burrs. Expanded joints should be
made using the appropriate tools and dies. Only where the cut pipe has either
deformation or a burr which significantly restricts the flow of gas will de-
burring be necessary.

Use of N2 internal inert gas shield

` Application

It is recommended that the pipeline to 13.31 Oxygen-free nitrogen should be supplied to the inside of the
be brazed should first be flushed to pre-assembled, unbrazed, pipework through a pressure regulator and flow
remove the air. This may be followed controller or flow regulating device.
during the brazing operating by a
continuous or intermittent flow as 13.32 If necessary, the purge gas should be fed from two ends of a T-joint.
necessary, to prevent the ingress of Care should also be taken to ensure that other pipelines in close proximity to
air. Pipe ends may be capped if the one being brazed do not oxidise due to heat transfer.
desired to direct the flow of N2 into
sections of the pipe or pipes to be
brazed. Particular attention should be
given to the gas shielding of T-joint
fittings
Safety

If necessary, the oxygen content of 13.33 If working for prolonged periods in very confined spaces, precautions
the ambient air should be monitored must be taken to avoid excessive build up of nitrogen, by ventilating the
space or by piping the shield gas safely out of the space.

Control of cylinders

13.34 The contractor and the site engineer must keep a record of nitrogen
cylinders held on a site. Nitrogen cylinders should be accounted for and

129


removed from the site at the end of the contract, and must not become mixed
up with medical gas cylinders.

Other installation processes

13.35 Oxygen-free nitrogen should also be used internally on pipework – as in
paragraph 13.31 – whenever annealing or hot forming of pipework is carried
out.

Inspection of joints

13.36 Joints brazed should be inspected in accordance with the following
procedure:

a. before pressure testing, the site engineer should identify a number of
fittings to be cut out for examination in order to establish the quality
of the finished joint. The exact number to be cut out will vary with the
size of the installation, but as a guide a ratio of one fitting per
200 installations should be cut out. In any event, a minimum of two
and not normally more than five fittings should be cut out for
examination;

b. the fittings cut out should be cut open (quartered longitudinally) and
examined. If unacceptable joints are found, adjacent fittings should be
cut out until the extent of any faulty workmanship has been
established. The joints should be assessed in accordance with
paragraphs 13.37 and 13.38;

c. the pipeline should be made good;

d. the pipe should be fully inserted up to the shoulder of the fitting.

Internal cleanliness

13.37 The tube and fitting should be internally clean and free from oxides and
particulate matter. Some heat burnishing may be apparent and is acceptable.

Penetration

13.38 Penetration of brazing alloy:

a. due to tolerances of the capillary space on these pipes and fittings, full
penetration of the brazing alloy may not occur and is not necessary;

b. the minimum penetration at any point on the joint must be three times
the wall thickness of the tube or 3 mm, whichever is greater.

Capping

13.39 Sections of pipeline should be capped as soon as they are completed,
to prevent the ingress of air.

Removal of flux residues and oxides

13.40 The residue of flux and oxide resulting from the brazing of copper-to-
brass/gunmetal/bronze fittings must be removed before components are
delivered to site. The following procedure should be used, or alternatively, one
which is no less effective may be substituted.

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13.41 Allow joints to cool naturally to room temperature or at least to a
temperature at which they can be handled. This is specifically for gunmetal
fittings which, if cooled (or quenched) from the brazing temperature by
dipping in cold water, could crack.

13.42 The flux residues should be removed by immersion in hot water and
brushing with stainless steel type wire brushes.

13.43 The oxides formed should be removed by immersing in a 5–10%
sulphuric acid solution at 65ºC (nominal) to which 25–50 g/litre of potassium
dichromate has been added. The component should then be thoroughly
rinsed in hot water at 80ºC (nominal); this should result in a bright, clean
component.

13.44 The fitting should be degreased if necessary and bagged.

Purging with the working gas

13.45 Purging should be carried out strictly in accordance with the
procedures given in ‘Validation and verification’.

Pipe supports

13.46 The pipeline should be adequately supported at sufficient intervals in
accordance with Table 21 to prevent sagging or distortion. Supports for
surface mounted pipework should provide clearance to permit painting of the
surface. Where it is essential for pipes to cross electric cables or conduit, they
should be supported at intervals on either side of the crossing to prevent
them from touching the cables or conduit. Supports should be of suitable
material or suitably treated to minimise corrosion and prevent electrolytic
reaction between pipes and supports.

Table 21 Intervals between copper pipe supports

Outside dia mm Maximum interval Maximum interval for
for vertical runs m horizontal runs m

12 1.2 1.0
15 1.8 1.2
22 2.4 1.8
28 2.4 1.8
35 3.0 2.4
42 3.0 2.4
54 3.0 2.7
76 3.6 3.0

13.47 Pipelines need not be laid with falls. In the case of vacuum, the
sub-atmospheric pressure will result in the evaporation of any moisture
entering the system. It is possible, however, for vacuum jars to overflow and
thus for systems to require flushing through.

13.48 The connection from individual vacuum terminal units into the main
unit should be taken from the top of the pipeline to avoid flooding other
vertical pipe drops during flushing. Each vacuum main riser should be
provided with a double valve arrangement to permit drainage when the
system is under vacuum: one of the valves should be lockable in the closed
position. No other sloping or drainage arrangements are required.

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13.49 Pipelines need further protection in certain circumstances as follows:

a. where pipes pass through walls, partitions or floors they should be
fitted with sleeves of copper pipes which conform to BS 2871 and be
provided with appropriate wall or ceiling plates;

b. in radiodiagnostic procedure rooms etc, radio frequency (RF) screening
by means of extended sleeves will be necessary. The advice of the
equipment manufacturer should be sought;

c. corrosion of pipes can occur where they are in contact with timber
treated with fire-resistant or flame-retardant compounds, for example
some timber used for roof trusses and floor joists.

13.50 This contact should be avoided by the use of impermeable non-metallic
materials in the area where contact may occur. PVC spacers or adhesive PVC
tape may be used for this purpose. If spacers are used they should not be
liable to drop out due to shrinkage or subsequent movement of the pipe or
timber.

13.51 Such precautions are not required where untreated timber is used or
where the treated timber is effectively sealed with paint or varnish before the
pipes are fixed to it.

Identification of pipelines

13.52 Pipelines should be identified in accordance with BS 1710 and colour
banding for the pipelines should be used outside of the plantroom. Colour
band identification (see Figure 19) should be applied near to valves, junctions,
walls etc. Each gas should be identified in 6 mm letters. Self-adhesive plastic
labels of approved manufacture may be used for this purpose. A band
150 mm wide is usually adequate. All colour-coded tapes applied by the pipe
manufacturers should be removed before the systems are identified, in
accordance with this paragraph.

13.53 Care should be taken to maintain pipeline identification when
periodical re-painting is undertaken. The direction of flow should be indicated.

Pipeline fittings

General

13.54 Pipeline fittings which may be attached to an MGPS include various
types of terminal unit, valves, area valve service units (AVSUs), and other
components such as emergency inlet ports.

Ceiling pendant fittings – rigid, multi-purpose type

13.55 The construction should provide segregation of functional extra low
voltage (FELV) electrical services by means of flexible partitions or conduit as
appropriate. Access to “live” components should be via panels which are
removable by means of tools only.

13.56 When these fittings include flexible connecting assemblies for the gas
supply, the method of attachment to rigid pipework or terminal units should
be by means of the appropriate non-interchangeable screw thread (NIST)
connector in accordance with BS 5682:1984.

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A 00E55 WHITE
Notes:
O2
1. Base colours as follows:

A = yellow ochre 08C35
B = light blue 20E51 A 20D45 FRENCH BLUE

2. All colours in this
N2O
diagram should be
taken to be
representative rather
than exactly accurate.
00E55 20D45
3. Reference numbers in
colour codes conform to
O2/N2O (50% mixture)
BS 4800:1972

FRENCH GREY 12B21 00E55

O2/CO2 (CO2 ≤5%)

B BLACK 00E53

Medical air

PRIMROSE 10E53 B

Medical vacuum

GREEN 14E53 A

NO (nitric oxide)
“Proposed”

20D45 10E53

AGSS

B BLACK 00E53

N2

Figure 19 Colour code identification for medical gas terminal outlets and pipe installations

133


13.57 The fittings should be provided with adequate venting to allow escape
of gas in the event of rupture of one or all of the medical gas services.

13.58 The recommended height for rigid pendants is 2000 mm above finished
floor level (FFL).

13.59 The use of medical air for pneumatically actuated pendants is covered
in Chapter 4.

13.60 The manufacturer should confirm that these requirements are met prior
to the installation of the equipment; this should be demonstrated during the
validation and verification procedures.

Flexible pendant fitting

13.61 These should comply with the requirements of BS 5682, as amended.
In particular, all loose assemblies should be provided with appropriate NIST
connectors.

Bed-head trunking/walling system

13.62 These fittings should generally be in accordance with HTM 2015
‘Bedhead services’. Separate compartments should be provided for electrical
services, nurse call/radio etc and medical gas pipelines.

13.63 Flexible connecting assemblies used within the fitting should comply
with BS 5682, as amended.

13.64 The medical gas compartment should be provided with ventilation by
means of louvres, slots, etc to prevent the accumulation of any gas in the
event of rupture of the medical gas pipeline services.

13.65 In some departments it is becoming fashionable to install medical gas
services within concealed recesses (or behind decorative panels, paintings, etc)
to engender a more domestic appearance. In such cases, adequate provision
must be made for ventilation, and the required space to permit connection and
disconnection of equipment should be considered. The covers should be clearly
labelled to indicated that medical gas equipment is installed within/behind.

13.66 There are two possible alternative installation procedures:

a. the connection between the pipeline and the trunking should be
considered as first and second fix, with the trunking being pre-piped
and certificated as complying with HTM 2022;

b. the connection between the trunking and the pipework should be as
paragraph 13.56.

Shut-off valves

13.67 All valves should be of the lever ball type, which open and close with a
90° turn.

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Provision of valves

13.68 Valves should be provided on items of plant and sources of supply to
permit servicing and isolation of the main components and to connect the
sources of supply to the pipeline distribution system. Lockable line valves
should be provided:

a. at the pipeline entry to a building;

b. at the pipeline exit from a building;

c. on branches, risers etc at the connection to the main pipeline.

13.69 All valves located outside the plantrooms, wherever possible, should be
provided with lockable, ventilated enclosures.

Area valve service units (AVSUs)

13.70 AVSUs are provided for user access in an emergency (or for
maintenance purposes). They comprise a ball valve installed within an
enclosure, with lockable door permitting locking with valve “open” or
“closed”. The means of emergency operation should not introduce the
possibility of injury. The AVSU should provide means for physically isolating
and blanking off the pipeline both upstream and downstream of the valve.
The means of isolation should be readily operable, blank both the pipeline and
the valve port and be visible when deployed. In the event of leakage of the
blanking device, gas must be freely vented and must not be able to enter
either the valve port or the pipeline section blanked.

13.71 In an emergency, the user must be able to gain access in order to
operate the isolating valves quickly and simply without the need for a key.
There are several methods of providing such emergency access, for example
break-glass panels, plastic push-out inserts etc. Whichever method is used
must be safe and secure, but must not provide a risk of injury to the user. The
method of emergency access must be obvious and clearly labelled, and its use
must be evident.

13.72 The appropriate NIST connector bodies, with self-sealing check-valves,
captive plugs or caps, should be provided upstream and downstream of the
blanking plate. AVSUs may be designed for a single pipeline service or
multi-services. Where the cover bears the name of the gas service it should be
gas-specific. In the case of multi-service AVSUs, the design should be such as
to permit the attachment of a hose assembly to any one or more of the NIST
connectors while the cover is locked. The AVSU may include provision for
pressure gauges/pressure switches by means of separate bosses.

13.73 The enclosure should have adequate ventilation to prevent the
accumulation of gas in the event of a leak. Pipe entries and other penetrations
should be sealed to prevent gas escape by routes other than the vents or
openings into the user space. The enclosure should be designed to facilitate
sealing of these entries on site.

13.74 AVSUs should be clearly labelled to indicate their function and the
areas/beds etc served. Emergency access should not compromise the labelling.

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Provision of AVSUs

General

13.75 AVSUs should be provided as follows:

a. for general wards – one valve near the entrance to the ward;

b. for intensive therapy units, recovery, special care baby units, etc – one
valve at the entrance plus additional valves to control pipelines serving
between four and eight beds. The latter should not control more than
half the outlets in any one department;

c. for operating departments – one valve at the entrance to the
department plus valves to control each suite, that is, operating room,
anaesthetic room and (if provided) the plaster room;

d. all other departments – one valve at entry;

e. for vacuum service, AVSUs should be provided to facilitate
maintenance and isolation of specific departments.

13.76 For other departments, such as day-care surgery units, this may result in
unrealistically high numbers of AVSUs. As a guide, where there are fewer than
ten terminal units, a minimum of one AVSU should be provided at the
entrance to the department.

13.77 If possible, in critical care areas such as ITUs and neonatal units, each Where pneumatically actuated
AVSU should control only half the total number of terminal units in each pendant fittings are used, the medical
space. Where two sets of terminal units are provided to each bed/treatment air supply is typically used for the
space, consideration should be given to using one AVSU for one of each pair power source. In this case, closure of
of sets. one of the medical air AVSUs may
inactivate the pneumatic function, as
13.78 These would be isolated by two separate AVSUs. In this case, the well as isolating half the terminal
NIST connectors should be clearly labelled showing which terminal units or units. The fact that the AVSU controls
pneumatic function are served, and which AVSU isolates each NIST. the pneumatic operation of such
devices should be clearly labelled on
both the AVSU and the relevant NIST
Labelling
connector in the pendant fitting. The
more sophisticated pendants may
13.79 All valves should be clearly labelled to identify the areas/departments
have three NIST connectors for
served. In addition, AVSUs should be labelled to identify the individual rooms
medical air – one for the pneumatic
etc controlled. All valves and AVSUs should have flow direction arrows.
function and two for terminal units
13.80 The AVSUs should be similarly labelled, indicating which terminal units
and which pneumatic function is isolated by each AVSU.

Pressure sensors

13.81 Pressure sensors to provide the alarm function will need to be fitted to
pipeline distribution systems. In all cases they should be installed in a location
which is adequately ventilated and having access for maintenance. They may
be incorporated within AVSUs. Pressure sensors should be factory set and be a
replacement item. They should be connected to the pipeline by means of a
minimum leak connector.

Pressure gauges

13.82 Pressure gauges are not usually required outside the plantroom of an
MGPS. If provided, however, they should similarly be installed in an

136


adequately ventilated location. They may be incorporated within AVSUs,
theatre supply fittings etc. They should be installed with isolation cocks.

Test points

13.83 Each supply plant, that is, liquid facility, manifold, compressor, pressure
swing adsorber (PSA) and blending plant, should be provided with a test point
comprising lockable valve and terminal unit for test purposes. This should be
within the plantroom or enclosure, and be sited immediately upstream of the
distribution pipeline isolating valve.

Emergency inlet port

13.84 Medical oxygen and 400 kPa medical air systems should be provided
with an emergency inlet port to the pipeline distribution system. This should
be located downstream from the main source of supply, to permit connection
of a temporary supply plant. The emergency inlet should comprise a lockable
valve and blanked, gas-specific connecting port, and should incorporate a
non-return valve.

13.85 An emergency inlet port is not required for 700 kPa surgical air
systems.

Line pressure alarms and safety valves

13.86 The purpose of the line pressure alarm is to warn users that the
nominal line operating pressure is out of limits and that gas mixtures, whether
supplied by a blender/mixer or by an anaesthetic machine, may deviate from
the clinical desired proportion. Local action can then be taken to adjust the
mixture, or when an anaesthetic machine is in use the reserve cylinders can be
brought into use. The low-pressure alarm for nitrous oxide/oxygen mixture
supply pipelines will warn of possible demand valve regulator failure so that a
portable cylinder can be made available. The high/low pressure limits have
been set to accommodate the design of most types of anaesthetic equipment
where differential pressure or low pressure may affect performance.

13.87 The line pressure safety valve provides limited safety from differential
pressure effects since the pressure at which maximum discharge occurs will
result in a differential much greater than that for which the anaesthetic
equipment has been designed. They are therefore strictly system protection
devices.

13.88 The commissioning of medical gas pipeline line pressure regulators,
warning and alarm systems, and pressure settings is crucial to performance of
anaesthetic equipment and patient safety; once commissioned, medical gas
pipelines are subject to strict permit-to-work procedures, and
decommissioning a complete system is highly disruptive to patient care and
introduces considerable risk.

13.89 Statutory obligations under the Pressure Systems and Transportable
Gas Containers Regulations require the periodic testing of pressure safety
devices. It is not appropriate to test a medical gas pipeline system by either
raising the line pressure regulator setting or manually unseating the relief
valve. Such action could result in failure of anaesthetic equipment, and in the
event of failure of the safety valve to re-seat, considerable gas loss and further
hazard. Medical gas pipeline line distribution systems should be provided with
a pressure relief device downstream of the line pressure regulator connected
by means of a three-way cock so that the safety device can be exchanged for
a “certificated” replacement in accordance with the frequency required by the
Regulations.

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14.0 Accommodation

Design and construction of plantrooms

Location of plantrooms

14.1 Cylinder gas/liquid supply systems should not be located in the same
room as medical air compressors, PSA systems or vacuum plants.

14.2 Manifold rooms, emergency/reserve manifold rooms for pressure swing
adsorber (PSA) systems, vacuum insulated evaporator (VIE) installations and
medical compressed air systems should be located near to the medical gas
cylinder storage area.

14.3 All manifolds, including the emergency reserve manifolds, may be
located within the same room. Manifold rooms should be located on an
external wall(s) to facilitate ventilation, which will be required at high and low
level.

14.4 The emergency/reserve manifold for liquid oxygen systems has
traditionally been located within the VIE compound, but it is preferable to site
the manifold separately. For new installations, these emergency/reserve
manifolds should be located separately.

14.5 It is preferable to site the manifold for medical air 700 kPa systems
within the operating department. However, the gas used is at high flows,
but the overall consumption is modest and therefore there may be little
disadvantage in sites remote from the cylinder store. (The number of cylinders
stored in buildings should be kept to a minimum.)

14.6 The medical air 700 kPa manifold room may be used as the ready-use
store for a small number of spare cylinders to be used on anaesthetic
machines.

Access

14.7 Access to manifold rooms should be from the open air, not from
corridors or other rooms.

14.8 Normal commercial lorry access is suitable for gas cylinder delivery
vehicles, but consideration should be given to the provision of a raised level
loading bay when this is justified economically on the basis of cylinder
handling costs.

14.9 Two doors should preferably be provided in a manifold room. One
should be large enough to facilitate cylinder handling and must be in an
outside wall. Exits must be free of all obstructions. Doors must open outwards.
All doors must normally be locked to prevent unauthorised access, but should
be provided with means of entry and exit in an emergency, for example by a
combination of a key in a break-glass box and a push-bar arrangement on the
inside.

138

14.0 Accommodation

14.10 The internal walls, including any internal doors of the manifold room,
should be suitable non-combustible 2-hour fire-resistant material as defined in
BS 476 Parts 4 and 8. Internal doors should be avoided where practicable.
Heat detectors should be provided.

Construction and layout of manifold rooms

14.11 The manifold room will contain the manifolds as well as cylinder racks
holding sufficient spare cylinders to replace one bank of each manifold and
the emergency/reserve manifold. Further replacement cylinders should be
supplied from the non-flammable medical gas cylinder store. The size of the
manifold room should therefore be determined from the size of the
equipment, as advised by the manufacturer. Adequate space should also be
allowed for cylinder handling.

14.12 A typical automatic manifold with two “duty” and two standby
cylinders is 1.8 m long and 0.6 m deep. One extra cylinder on each bank adds
approximately 0.5 m to the overall length, so that a 2 x 6 manifold is
approximately 4 m long.

14.13 All medical gas manifolds may be installed in the same room.
Additional floor area should be provided to accommodate separate storage
racks for each gas. The racks should be designed along the lines of those on
the manifolds, but the stored cylinders may be closer together. Racks should
conform to BS1319. Wooden racks should not be used. With the exception of
N2O/O2 mixtures, under no circumstances should rooms contain gas cylinders
other than those appropriate to their manifolds.

Heating and ventilation of plantrooms

14.14 Ventilation louvres should be provided at both high and low levels for
all manifold rooms, to allow circulation of air. As a guide, well-separated
openings equivalent to at least 1.5% of the total area of the walls and room
should be provided. For example, given a manifold room 5.0 x 4.0 x 2.4 m
with a total area of the walls and ceiling of 63.2 m3, the total free open area
for ventilation required is 1 m3.

14.15 The aspirated air inlets should, if possible, be located externally, and
should vent to a safe area away from ventilation plant intakes etc. However,
they should not be taken as an alternative to the provision of an adequate air
supply for cooling purposes.

14.16 All vents should be vermin/bird-proof.

14.17 PSA and medical air compressors liberate, under maximum flow
conditions, considerable heat. Moreover, these plants aspirate air for
breathing purposes. Generous natural ventilation should be provided. The
ambient temperature of manifold rooms and plantrooms should be
maintained within the range of 10ºC to 40ºC. The ventilation rates should
ensure that the plantroom temperature does not exceed ambient temperature
by more than 10ºC.

14.18 In some cases it may be necessary to provide mechanical ventilation for
plantrooms, with supply air directed towards the compressor air intakes and
inter-/after-coolers. It should rarely be necessary to provide cooling.

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14.0 Accommodation

14.19 Manifold rooms may be used to store small numbers of nitrous
oxide/oxygen cylinders intended for portable use; these are taken from the
main cylinder store for the purpose of temperature equilibration, before being
delivered to wards etc.

14.20 To achieve temperature equilibration, additional heating may be
required; the natural ventilation must not be reduced. Where such heating is
provided, it should be preferably by indirect means, for example steam, hot
water or warm air. Naked flames and exposed electric elements should not be
used, and excessive surface temperature should be avoided. If necessary,
cylinders should be protected from excessive heat. Any primary heat source
should be located in a safe position, preferably remote from the manifold
room.

14.21 Additional space may be provided in such manifolds for holding
cylinders used on trolleys (in addition to spare cylinders intended for use with
the pipeline system) to allow temperature equilibration displays as appropriate.
Cylinder recognition charts, conforming to BS 349:1973 or BS 1319, should be
prominently displayed as appropriate.

Lighting

14.22 Manifold rooms should be provided with lighting to an illumination
level of 150 lux (15 lumens/sq ft) by means of bulkhead lighting fittings to
IP 54 BS 5490:1977. Plantrooms other than manifold rooms should be
provided with a lighting level of 200 lux (20 lumens/sq ft).

Noise control

14.23 Plantrooms should be designed and constructed to ensure the
satisfactory control of noise emission. The effect of two vacuum pumps or
compressors running together, in the case of duplex installations, and three or
more in the case of multiplex installations, will be to increase the free-field
noise level outside the plantroom by 5 dBa for each additional pump or
compressor operation over and above the specified limits. Consideration
should be given to providing acoustic enclosures to reduce the free-field noise
levels in noise-sensitive areas adjacent to plantrooms.

14.24 Acoustic enclosure and/or plantroom design must not inhibit normal
cooling functions or maintenance activities.

14.25 Free-field noise levels should be given to the architect to assist in
acoustic design of the plantrooms.

14.26 The discharge from some vacuum pumps may require silencing,
although it should be noted that rotary pump exhausts are not likely to require
silencers.

14.27 Compressors and pumps should be mounted on properly selected anti-
vibration mounting, where necessary, to minimise transfer of noise and
vibration to the structure of the building.

14.28 All pipework and electrical conduits connected to the plant should be
fitted with flexible connectors where necessary, to prevent the transmission of
noise and vibration along the pipelines and conduits.

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General

15.1 This section covers the validation and verification and filling for use of
MGPS. The requirements for anaesthetic scavenging systems are also covered
in paragraphs 15.118–15.139.

15.2 The test procedures and methods are also included in this chapter.

15.3 The objective of testing and commissioning is to ensure that all the
necessary safety and performance requirements of the MGPS will be met.
Testing and commissioning procedures will be required for new installations,
additions to existing installations and modifications to existing installations.
The scope of work will dictate the specific test programme required. This is
described in more detail in paragraphs 15.14–15.16.

15.4 This chapter describes the tests required and the test methods. Tests
are listed in Appendix A and the associated forms in Appendix B.

15.5 For extensions comprising fewer than 20 brazed joints, all the tests
may be performed with the working gas – the pressure test being replaced by
a leak test. An extension comprising more connections would, however, be
deemed to be a small installation, requiring all the appropriate tests to be
carried out, up to the final connection (and leak test). For the purpose of
ascertaining the number of joints, a straight coupling comprises two joints
and a tee comprises three joints.

15.6 For modifications and extensions (except for the final connection), all
work should be performed with an inert gas shield, to avoid widespread oxide
contamination and, thus, it is essential that a physical break is employed
between the pipeline being modified and any “in-use” systems and
prohibition labels are affixed to outlets in areas occupied by patients and that
all the identity, purity and quality tests are carried out. On a minor
modification, from which existing terminal units would not be removed, it
may not be practical to carry out a pressure test on the new carcass and
therefore this could be deleted. All other tests would be required, including
the pipeline pressure test.

15.7 The programme of tests is divided into three phases:

a. tests and checks on the pipeline carcass;

b. tests and commissioning of the complete pipeline system (with terminal
units installed) for safety, performance and particulate contamination
using test gas;
c. filling of the systems with specific gases, quality tests and proof of the
identity of those specific gases prior to use for patient care.

15.8 The basic rationale for the tests is depicted as a decision tree in
Figure 20.

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15.9 The personnel and test equipment needed for these tests are listed Systems that are not to be taken
together with the test requirements in Table 22. The particulate immediately into use should be filled
contamination of all pipeline systems may be checked using dry, oil-free with medical air and left under
medical air to establish that the pipeline has been constructed correctly and pressure. Nitric oxide systems should
is not contaminated. Successful completion of the commissioning tests be filled with nitrogen.
normally indicates the end of the installation contract. The systems may then Because of the possibility of oil
be left under pressure, filled with medical compressed air, for an indefinite contamination, systems other than
period. Responsibility for the system during this period needs to be clearly medical air supplied from compressors
defined in the contract. should be filled with medical air from
cylinders
Table 22 Personnel and test equipment requirements

Paragraph Test Personnel Equipment

5 Pipeline carcass CSO & CR

5.1 Labelling and marking CSO & CR
5.2 Sleeving and supports CSO & CR Pressure device
5.3 Leakage CSO & CR
5.7 Cross-connection CSO & CR

6 Pipeline system

6.1 Leakage CSO, CR & AP Pressure device
6.7 Area valve service units CSO, CR & AP Pressure device
6.10 Cross-connection CSO, CR & AP
6.15 Flow and pressure drop CSO, CR & AP Special test device
6.16 Mechanical function CSO, CR & AP Test probes
6.17 Gas specificity CSO, CR & AP
6.18 NIST connectors CSO, CR & AP
6.20 System performance CSO, CR & AP Metered leaks and
special test device
6.24 Supply systems CSO, CR & AP
6.26 Pressure safety valves CSO, CR & AP
6.28 Warning systems CSO, CR & AP
11.1 As-fitted drawings CSO & AP

7&8 Purging and filling CSO & CR

9 Particulate contamination CSO, CR, QC Particulate matter
and quality & AP tester, oil, water,
CO and CO2
measuring devices

10 Gas identification CR, QC & AP O2 analyser and
N2O meter

13 Anaesthetic gas CR & AP AGS test device
scavenging systems and induced flow
test device

Key CR Contractor’s representative AP Authorised person (MGPS)
CSO Contract supervising officer QC Quality controller

15.10 Tests for cross-connection are made on the complete pipeline system.
These tests are of fundamental importance to the safety of the pipeline
systems.

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Figure 20 Decision tree for testing and commissioning
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15.11 All supply systems and their major components should have certificates
(as specified in Model Engineering Specification C11) which show that they
meet the design requirements of the pipeline system.

15.12 Validation and verification should only be undertaken by contractors The concept of the existing
who are registered to BS EN ISO 9000 with their scope of registration Quality Assurance BSI Schedule
defined to include commissioning. QAS 3720.1/206 is currently under
review. Further guidance will be given
15.13 All relevant tests should be carried out by the persons listed in Table when appropriate
22 and witnessed by the appropriate persons, who must record the results
of the tests in writing for the hospital authority.

Summary of tests

Tests and checks on the pipeline carcass

15.14 The following tests must be carried out after installation of the pipeline
carcass but before concealment:

a. visual check of pipeline labelling, marking, sleeving and support;

b. leakage test;

c. documented tests for cross-connection;

d. valve tests for closure, zoning and leakage.

Tests on the pipeline system

15.15 The following tests must be carried out after complete installation of
the pipeline system:
a. tests for leakage on each medical gas pipeline system;

b. tests of area valve service units (AVSUs) for closure, zoning and correct
control of the terminal units involved;

c. tests for cross-connection, flow, pressure drop, mechanical function
and gas specificity of the terminal units and for cross-connection,
mechanical function and gas specificity of NIST connectors;

d. performance tests of the pipeline system;

e. functional tests of all supply systems;

f. inspection of safety valve certification;

g. tests of warning systems;

h. tests for particulate contamination. These tests may be carried out with
either medical air or after purging and filling with the specified gas.
If the system is not to be taken into immediate use, the tests for
particulate contamination should be carried out with medical air and
the system then left under pressure.

Tests before use

15.16 The following tests must be carried out after purging and filling with
the working gas:

a. test for particulate contamination;

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b. test for gas identities;

c. tests for gas quality;

d. checks of the labelling of AVSUs (to include gas label, flow direction
arrow and area served.

General requirements for testing

General

15.17 A physical break must always be used between existing pipeline
systems, and any in-use system and any system filled with purge gas. This can
be achieved either by deploying the spades/blanking plates incorporated in
area valve service units (AVSUs) or by cutting and capping the pipe. Full-size
disc “danger do not use” prohibition labels should be fitted to outlets taken
out of service.

15.18 The tests described in this document must all be carried out, in the
order given, for new installations. It may be necessary to modify the test
programme slightly for modifications or extensions to existing systems. Care
must be taken, however, to ensure that the basic principles are followed.
Paragraph 15.29 gives details of the tests required for modifications/
extensions to existing systems.

15.19 Pressure testing for leakage is carried out in two stages for pressure
gas systems. The first pressure tests are applied to the pipeline carcass, the
second to the whole installation, which may include terminal units and
medical supply units as appropriate. There is a third stage, which applies to
vacuum systems only. The whole installation is tested with the vacuum plant
in operation.

15.20 Purging and testing must be carried out with clean, oil-free, dry air or
nitrogen, except for those tests where medical air or the specific working gas
is prescribed. All test gases must meet the particulate contamination
requirements of paragraph 15.95. The shield gas may be used for the leakage
test on the pipeline carcass described in paragraph 15.39. Medical air from
the compressor plant may be used to test medical air and vacuum systems,
provided the quality tests (including those for particulate contamination), as
discussed in paragraphs 15.88–15.105, have been carried out. Cylinders must
always be used as the source of test gas for oxygen, nitrous oxide,
oxygen/carbon dioxide and oxygen/ nitrous oxide systems in order to prevent
the possibility of contamination with oil. Argon should be used for testing
nitric oxide systems.

The terminal units should all be 15.21 Before the pipeline system tests are carried out, every terminal unit in a
marked “Do not use” before system under test must be labelled to indicate that the system is under test
modifications have started and that it should not be used.

15.22 Terminal units are required to be supplied with such labelling affixed.
Special connectors will be needed to introduce test gas into different pipeline
systems. These must be of distinctive construction and permanently labelled
with their function and the contractor's name. The location of special
connectors on the site must be recorded and should be subject to routine
inspection under a planned preventative maintenance (PPM) system.

15.23 The results of all tests must be part of the permanent records of the
hospital and should show details of the services and areas tested. The test

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procedures are outlined in paragraph 15.140. Examples of the appropriate
forms are given in Appendix A. All signatories are entitled to copies of the test
forms. The procedure for filing and retaining these forms should be included in
the local operational policy.

15.24 During all pressure tests, the system under test must be physically
disconnected from the source of pressure whilst the test is in progress. In the
case of compressed air systems, the pressure at the plant must be reduced
below pipeline distribution pressure.

15.25 All errors found during testing must be rectified and the relevant
systems must be retested as appropriate before the records are signed.

15.26 The contractor must provide all forms, labour, materials, instruments
and equipment required to carry out the tests described in paragraphs
15.37–15.85. This must include all cylinders of test gas together with medical
gas probes and the test device described in Appendix C.

15.27 The quality controller (QC) should provide the test equipment specified
in Appendices E, F and G.

15.28 The sequence of tests given in paragraphs 15.44–15.78 and
15.86–15.110 must be maintained. Where a test is repeated one system at a
time (for example cross-connection), the order in which the systems are tested
may be decided on-site by consultation between the contract supervising
officer and the contractor's representative.

Modifications, extensions or repairs to existing systems

15.29 Where modifications, extensions or repairs to existing systems
are carried out, the tests and the sequence of tests summarised in
paragraph 15.14 should be followed as far as possible. In any case, great care
must be taken to ensure that the principles of the tests are followed; for
example, leakage tests should always be carried out before cross-connection
tests.

15.30 The permit-to-work system should always be followed whenever any
work is carried out on an existing system. The authorised person (MGPS)
should act on behalf of the management and would not, therefore, be a
member of the contractor’s staff.

15.31 Whenever modifications or extensions are carried out, it is always
advisable to test both the existing system and the new system separately,
before the break-in is made. Existing systems should be tested to determine
their performance and to identify any potential limitations which may arise as a
result of modifications. Where there is any doubt as to the cleanliness, it is
obviously desirable that tests for particulate contamination should also be
carried out on the existing system prior to any break-in. It is the responsibility
of the hospital authority to ensure that these tests are carried out prior to the
design phase of any modifications or extensions. It is the responsibility of the
management to ensure that remedial work is carried out on an existing system.

15.32 The tests for particulate contamination on any extension or
modification should only be carried out with medical air.

15.33 The exact tests carried out will obviously depend on the nature of the
modification/extension. A specification should be prepared for the performance
of the completed system. This specification should be as close as possible to
that given in Table 23.

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Table 23 Validation and verification: pressure during pipeline system tests

Medical gas Pipeline distribution Terminal unit Max pressure drop Min pressure (this Plant pressure
pressure kPa test flow l/min in pipeline at may vary by +/–5% kPa
(see ‘Design system design flow between max flow
considerations’ kPa and static condition)
for design flows kPa

O2 400 10–100 40 370 430–490
N2O, NO 15
Medical air 20–80
400 kPa

O2/N2O 400 20 90 310 430–490
mixtures 275
inhalationary
gasps

Surgical air 770 350 110* 700 kPa at see ‘Design
700 kPa 350 l/min considerations’
(max 900 kPa at
no flow condition)

Vacuum 53.3 kPa 40 26.6 kPa 40 kPa
(400 mm Hg) (200 mm Hg) (300 mm Hg)
below standard
atmospheric
pressure of
101.3 kPa
(760 mm Hg)

* To the back of the local regulator or terminal unit.

15.34 Existing compressed air systems will have been designed to provide
250 l/min at the terminal unit in accordance with HTM 22 (1978). It may not
be possible for such systems to provide 350 litres l/min, as specified in Table 4
Chapter 4, and there may be circumstances where this would be acceptable.
This should be clearly stated in the specification for the performance of the
completed system. However, every effort should be made to comply with the
performance and quality specification given here.

15.35 It may be necessary to repeat some of the system performance tests
such as flow and pressure drop, at selected terminal units on the completed
system to demonstrate satisfactory performance (see paragraph 15.33).

15.36 The break-in to the existing system should be carried out with an inert
gas shield where practical, and a physical break must always be made between
the existing in-use system. A leak test must be carried out using a suitable leak
detection fluid on this joint at working pressure, and the joint purged with the
working gas. Fluxless brazing should, of course, be used. ‘Danger – do not use’
labels should be affixed to outlets taken out of service in areas occupied by
patients.

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Requirements for pipeline carcass tests

Labelling and marking

15.37 A visual check must be made on each pipeline system to ensure that
the pipelines are labelled in accordance with the contract specification, and
that the terminal unit base blocks are marked in accordance with
BS 5682:1984.

Sleeving and supports

15.38 A visual check must be made on each pipeline system to ensure that
the pipelines are sleeved and supported in accordance with the contract
specification.

Leakage

15.39 The aim of this test is to establish that there is no leakage from the
piped medical gas systems. This is best shown by the use of sensitive pressure-
measuring equipment. With suitable equipment it is possible to make such
measurements during a relatively short test period, which may be more cost-
effective and will minimise errors which arise as a result of temperature
change.

15.40 The pressure drop during a test period of 2–24 hours must be less Within large volume systems it may be
than 0.025% per hour. The pressure drop must be corrected for variations preferable to test small sections of the
due to temperature (see Appendix B). Systems must be tested at a working system individually
pressure of 18.0 bar g for medical compressed air systems for surgical use,
10.0 bar g for all other compressed medical gas systems and 7.0 bar g for
vacuum systems. This test should be carried out on the pipeline carcass with
the area valve service units or other valves open.

15.41 During pressure testing, any safety valves and pressure-sensing devices
installed may be removed and the connections blanked off.

15.42 It is not desirable to cross-link the carcasses to form a single system for
the purpose of the carcass leakage test.

Cross-connection

15.43 The contractor must test for cross-connection and document the results
of these tests.

Requirements for pipeline system tests

Leakage from total compressed medical gas systems

15.44 There must be no links between the MGPS.

15.45 This test must be carried out on the pipeline system with the supply
system disconnected, so that gas cannot be supplied to the pipeline from the
supply system. For the purpose of this test, the supply system extends to the
last valve(s) detailed on the appropriate schematic drawing. This point should
be identified on the contract drawings.

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15.46 A leakage of not more than 0.02 l/hour is permitted from each
terminal unit.

15.47 The system must be tested at pipeline distribution pressure. After a
period under test, a pressure drop may be observed in the system. The
pressure drop must not exceed the value calculated from the formula:

p = 2n.h
V

where:

p = gauge pressure drop, in kPa

n = number of terminal units

h = number of hours on test (between 2 and 24)

V = volumetric capacity, in litres, of the pipeline system at atmospheric
pressure.

15.48 The following points should be noted:

a. with large volume systems, it may be preferable to test small sections of
the system individually;

b. the pressure change must be corrected for variations due to
temperature (see Appendix B);

c. where leakage is in excess of the specified limits, the source of the leak
must be identified and the fault rectified;

d. the volume of the system may be measured by the procedure given in
Appendix H.

Leakage into total vacuum systems

15.49 Prior to testing, the vacuum plant should be operated to remove any
condensation in the system. With the system at pipeline distribution pressure
and with the source isolated, the pressure increase in the pipeline must not
exceed 10 kPa after 1 hour. There is no additional allowance for temperature
correction in this test.

Closure of area valve service units

15.50 For pressurised systems the system upstream of the closed valve under
test must be at pipeline distribution pressure and the downstream line should
be evacuated by using an opened flow meter or probe. This upstream
pressure must be recorded and there should be no pressure decrease
upstream from the valve over a period of 15 minutes.

15.51 In the event of loss of pressure it will be necessary to identify the faulty
AVSU. This may be accomplished by introducing a pressure to about 1 bar g
after AVSUs, and checking for increased pressure.

15.52 For vacuum systems, the systems on the supply plant side of the closed
valve must be at pipeline distribution pressure and the terminal unit side
should be at atmospheric pressure. This upstream pressure must be recorded
and there should be no loss of vacuum upstream of the valve over a period of
time, typically 30 minutes.

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15.53 In the event of loss of vacuum, it will be necessary to identify the faulty
AVSU. This may be accomplished by introducing a vacuum of about
200 mm Hg after AVSUs and checking for any increase in vacuum.

Zoning of area valve service units and terminal unit identification

15.54 With pressure in one system at a time, a check of all AVSUs must be
made to ensure that each AVSU in the pipeline under pressure is labelled and
controls only those terminal units intended in the design (see opposite). The
labelling of each terminal unit must be checked to ensure that it is correct and
is in accordance with BS 5682:1984 (1992).

15.55 The AVSU under test should be closed; all other AVSUs should be open.

15.56 For pressurised systems, the system upstream of the valve should be Where pneumatically-activated
at pipeline distribution pressure and the downstream section should be de- pendant fittings are installed, a check
pressurised to about 1 bar. All downstream terminal units should be checked should be made to ensure that the
for pressure and the results recorded. During the test, the recorded pressure power source of medical air has been
of 1 bar, or thereabouts, will fall depending upon the number of terminal taken from the correct AVSU
units controlled, and it may be necessary to ‘top up’ the pressure to
complete the test.

15.57 For vacuum systems, the downstream vacuum should be about A downstream pressure or vacuum is
200 mm Hg (27 kPa) and all downstream terminal units should be checked required to positively identify terminal
for increase in vacuum. (As forpressurised systems it may be necessary to units controlled, and to discount the
“top up” the vacuum to complete the test. affect of a leaking terminal unit if the
pressure were zero
Similar valve closure and zoning tests
Cross-connection
should be performed for main service
valves
15.58 Each system in turn, including vacuum, must be checked as follows
to ensure that there is no cross-connection between pipelines for different
gases and vacuum.

15.59 Cross-connection tests should not commence until all installations are
complete. All AVSUs and any other valve in the distribution system must be
open on all systems. The system under test must be at pipeline distribution
pressure and all other systems must be at atmospheric pressure. A check must
be made to ensure that gas flows through every terminal unit of the system
under test, one at a time, and that there is no gas flow through any other
terminal units.

15.60 The test must be repeated on each system in turn, including vacuum,
preferably at one session.

15.61 There must be no cross-connection.

15.62 This test must be repeated in full if any subsequent modifications are
made to the pipeline system.

Flow and pressure drop at terminal units

15.63 The pressure drop must not exceed the values in Table 1 of
BS 5682:1984 (1992), as amended (but see also Table 23 for surgical air
systems and oxygen/carbon dioxide) when each terminal unit is tested one at a
time, using the appropriate device described in Appendix C, at its specified
flow with the pipeline at pipeline distribution pressure.

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Mechanical function of terminal units

This test requires that the terminal 15.64 It must be demonstrated for each terminal unit that the appropriate
unit is complete with its fascia in place gas-specific probe can be inserted, captured and released, and that the probe
does not swivel in any horizontally-mounted terminal units. In vertically-
mounted terminal units the probe should be capable of twisting without
undue force.

Gas specificity of terminal units

15.65 For each terminal unit, it must be demonstrated that gas is released
only when the correct probe is inserted, that no probe is captured, and that
no gas is released when probes for all other gases are inserted. All probes
used for this test must be certified to BS 5682:1984 (1992).

NIST connectors

15.66 For each NIST connector, it must be demonstrated that normal flow of
gas is achieved only when the correct NIST probe is inserted and mechanical
connection made. The NIST probes for all other gases must not make
mechanical connection.

It is not necessary to carry out these 15.67 It must be demonstrated (except for vacuum) for each NIST connector
tests on factory connected NISTs that the self sealing device substantially reduces the flow of gas when the nut
which are incorporated into certified and nipple is removed.
assemblies
Performance tests of the pipeline system

15.68 Each pipeline system in turn should be operated at the specified design
flow by introducing a number of calibrated metered leaks. It must then be
verified at representative terminal units throughout the installation, that at the
normal test flow for these terminal units, the pressure does not fall below the
values given in Table 23.

15.69 This test requires that:

a. the metered leaks are stamped to show the jet size;

b. the flow of test gas at the test pressure is determined for each jet size
used;

c. the design flow is corrected for the density of the test gas;

d. the leaks must be placed where the downstream flow could be at least
equal to the total flow through the leak. These leaks may be placed at
terminal units, AVSUs or NIST connectors as appropriate. This is not
likely to be the end of the branch;

e. approximately 20–25% of the terminal units distributed throughout the
system must be tested with the device described in Appendix C, to
measure the pressure at the specified flow.

15.70 For large vacuum systems, the specified design flow may be set by the
procedure given in Appendix G. With the system running at the design flow,
it must then be verified, at representative terminal units throughout the
installation, that at the normal flow for these terminal units (40 l/min) the
pressure drop does not exceed the value given in Table 23. It may be
necessary to incorporate an additional uncalibrated leak at the plant test point
to stabilise the vacuum level to 450 mm Hg at the plant/pipeline interface.

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15.71 For mixtures of oxygen/nitrous oxide (50% v/v), each terminal unit must
be tested to ensure that a peak flow of 275 l/min for 5 seconds can be
achieved with a minimum pressure of 310 kPa (3.1 bar g). This is the minimum
pressure for satisfactory operation of demand valve regulators. This is in
addition to the total system flow test.

Functional tests of supply systems

15.72 For all systems, prior to carrying out any tests, check that the provision
is in accordance with Table 2.

15.73 All supply systems must be tested for normal and emergency
operation, according to the manufacturers' manuals and contract
specifications. Check lists must be written for the appropriate functions of all
the items of plant in the installation. Particular attention should be paid to
the following:

a. manifold installations – test gas may be used for the following
checks:
(i) check that each half of all automatic manifolds operate at the The appropriate alarm functions may
specified pressures. A standard gas cylinder must be used to be tested at the same time
pressurise the manifold and a controlled leak allows observation
of the operating pressure;
(ii) check the operation of all pressure regulating valves and non
return valves;
(iii) check the operation of any heaters, where fitted;
(iv) check that the manifold can deliver design flow rate;
(v) check the operation of the emergency manifold;
(vi) check that all plant operates with start-up in the correct sequence
when switched to the stand-by power source;
(vii) check the operation of the warning and alarm system and the
plant indicator unit;

b. liquid oxygen installations:
(i) check that the heater unit, where fitted, vapouriser pressure
controls, relief valves, pressure controls and warning devices
operate according to specification;
(ii) check the function of the changeover to the reserve manifold;
(iii) check that operation is at maximum specified flow;
(iv) check the operation of the warning and alarm system and the

c. compressed air plants:
(i) check for the correct rotation and current at full load;
(ii) check for excessive vibration and noise;
(iii) check all automatic operations;
(iv) check the changeover to reserve manifold;
(v) check the function of automatic drains and by pass valves;
(vi) check the operation of all plant at its maximum continuous rating;
(vii) check that the power consumption of the compressed air plant is
in accordance with the contract specification;
(viii) check the accuracy of all pressure gauges and thermometers;
(ix) check that the insulation resistance and effectiveness of earthing of
all electrical items are in accordance with IEE regulations – extant
edition;

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(x) check that all plant operates with start up in the correct
sequence when switched to the standby power source;
(xi) check that the position of the air intake to the compressors is in
accordance with the contract specification;
(xii) check the operation of the warning and alarm system and the

d. vacuum plants:
(i) check for the correct rotation and current at full load;
(ii) check for excessive vibration and noise;
(iii) check all automatic operations;
(iv) check the operation of non-return valves and sensors;
(v) check the function of drains and bypass valves;
(vi) check the operation of all plant at its maximum continuous
rating;
(vii) check that the power consumption of the vacuum plant is in
accordance with the contract specification;
(viii) check the accuracy of all vacuum gauges and thermometers;
(ix) check that the insulation resistance and effectiveness of earthing
of all electrical items are in accordance with IEE regulations –
extant edition;
(x) check that all plant operates with start-up in the correct
sequence when switched to the stand-by power source;
(xi) check that the position of the vacuum discharge is in accordance
with the contract specifications;

e. oxygen concentrator plant:
(i) check the operation of cycling systems for each sieve pair;
(ii) check the control system to regenerate the sieves in relation to
pipeline demand;
(iii) check the operation of automatic changeover to standby
molecular sieve in the event of failure of duty sieve, low O2
concentration, dryness or pressure;
(iv) check the operation and calibration of sensors for O2
concentration, dryness and pressure, and all pressure gauges and
thermometers;
(v) check the operation of all pressure-regulating valves and non-
return valves;
(vi) check the activation of appropriate fault indicator and associated
volt-free contacts, and that the sub-assembly remains in this
mode of operation until the fault has been rectified;
(vii) check the operation of each dryer sub-assembly function
indicator;
(viii) check operation in the event of a power failure, to ensure that
all valves close in a fail-safe mode and to ensure the operation of
the emergency manifold;
(ix) carry out the same checks for each compressor as for
compressed air plant;
(x) check the operation of all plant at its maximum continuous
rating and check that the design specification for flow, pressure
and quality is achieved;
(xi) check the operation of the warning and alarm system and the
plant indicator unit.

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Pressure safety valves

15.74 Check that the specified pressure safety valves, line valves and non-
return valves have been fitted.

15.75 Verify that the valves are certified to operate in accordance with the
contract specification and conform to BS 6759:Part 2: 1984.

Warning systems

15.76 The operation of warning systems should be tested in all operating and
emergency conditions for one function at a time and one system at a time.
Particular attention should be paid to the following:

a. that all warning systems operate within the specified tolerance limits at
all operating parameters and fault conditions, and can be seen and
heard as specified in Table 19;

b. that systems react correctly following return to normal status;

c. that all panels and switches are correctly marked;

d. that all warning functions on all stations operate correctly;

e. that the warning system will operate from the essential supply standby
power source;

f. that all systems are labelled to show the areas they serve, or as detailed
in the contract specifications.

15.77 The following tests should also be carried out:

a. for central alarm panels, check that the operation of the mute switch
cancels the audible alarm and converts the flashing signals to steady;

b. for repeater alarm panels, check that the mute switch cancels the
audible alarm and that the flashing signals are converted to steady only
when the central alarm panel;

c. for area alarm panels, check that the operation of the mute switch
cancels the audible only;
d. check power failure operates red “system fault” indicator and audible;

e. check that a contact line fault operates the “system fault” indicator,
the alarm indicator and the audible;

f. check communication/wiring faults between central and repeater
alarms operate the “system fault” indicator and audible;

g. check audible reinstatement for each alarm panel;

h. check that the audible can be continuously muted via operation of the
internal push-button for gas service alarm condition only;

j. check for correct identification of each gas service on alarm panels and
“departmental” or plant specifying labels.

Verification of as-fitted drawings

15.78 The “as-fitted” drawings should be checked to ensure that all variations
from the contract drawings have been recorded.

154


Filling with medical air

With the exception of medical 15.79 An indefinite time may elapse after completion of the MGPS
compressed air systems supplied from construction contract before the MGPS are to be used. The construction
compressors, medical compressed air contract may be written in the expectation that this will happen. In such
cylinders should be used. For nitric circumstances the contract should require that the particulate contamination
oxide systems, oxygen-free nitrogen and odour tests specified in paragraphs 15.95 and 15.105 are carried out as
cylinders should be used an interim measure, using medical air as the test gas. Satisfactory completion
of these particulate contamination and odour tests may then signify the
completion of the construction contract.

15.80 It is the responsibility of the client to ensure that proper provision is
made in a specific contract for the maintenance, integrity and any special
connectors which may be required during this interim period.

15.81 All MGPS should be left filled with medical air at pipeline distribution
pressure until they are filled with the specific working gas shortly before use.
The medical vacuum pipeline need not be maintained under vacuum.

15.82 Provision should be made for regular running and maintenance of all
supply plant during such an interim period.

15.83 Details of the work carried out, as well as records of the system
pressures, should be recorded. This information is required in order to
demonstrate that the systems have been satisfactorily maintained under
pressure during this interim period. Tests for particulate contamination should
be carried out after the systems are filled with the specific gas. The extent of
the tests is at the discretion of the quality controller (QC).

15.84 Check that a “Danger – do not use” label is affixed to each terminal
unit.

Special connectors and cylinders may 15.85 When the construction contract has finished, the contractor should
be required to maintain the systems record the removal of all special connectors and cylinders from site.
under pressure

Purging and filling with specific gases

15.86 Each pipeline system must be purged with the specific working gas
shortly before use. The following conditions should apply:

a. all sources of test gas must be disconnected;

b. all special connectors must be removed from site;

c. each pipeline system must be at atmospheric pressure with all AVSUs
open;

d. each system must be filled to pipeline distribution pressure with the
specific gas from the supply system;

e. with the supply system on, each terminal unit must be purged at a
known flow with a volume of gas at least equal to the volume of the
pipeline being tested;

f. all oxygen, nitric oxide, oxygen/carbon dioxide mixtures, nitrous oxide,
and nitrous oxide/oxygen mixtures released during the purging process
must be disposed to a safe place.

15.87 Purging is not necessary for vacuum systems.

155


Quality of compressed medical gas systems

General

15.88 The objective of these tests is to establish whether the pipeline has
been contaminated during construction or modification. With the exception of
the particulate contamination and odour tests, these tests must be carried out
after the systems have been filled with the specific working gas. Oxygen,
oxygen/carbon dioxide, nitric oxide, and nitrogen must be vented to a safe
place. These tests are not required on a vacuum system.

15.89 These test procedures are based on existing practice. The particulate
contamination test is subjective in that it requires the quality controller (QC) to
make a judgement on whether or not particles are visible on the filter.

15.90 The oil, water, carbon monoxide and carbon dioxide tests are intended
to be carried out with detector tubes. These tubes give a quantitative response
and are not intended for re-use. The tubes should be agent-specific since non-
agent-specific (poly-test) tubes can respond to various agents such as volatile
inorganic compounds, giving misleading results. A dewpoint meter could be
used for water content.

15.91 These tests must be carried out on a representative sample of terminal
units in each system at the discretion of the QC. The sample must include as a
minimum the most distant terminal unit on each branch, normally the first
terminal unit to be tested. Depending on the results of the tests, the QC
should decide the number and location of additional terminal units to be
tested.

15.92 These tests are summarised in Table 24.

15.93 Medical compressed air (and PSA) plant should be tested for quality
before the pipeline distribution system is filled with the working gas.

15.94 Quality tests should be carried out on the plant as well as on the
pipeline distribution system.

Particulate matter

15.95 The test for particulate matter should be carried out at every terminal
unit. It can be carried out either after completion of the construction phase or
after the system has been filled with the specified gas. If, after construction,
the system is to be left filled with medical air, the particulate test would be
completed first. Once the system is filled with working gas, it would not
normally be necessary to repeat the test at every terminal unit. The actual
number of terminal units sampled is at the discretion of the QC. It would,
however, be necessary to repeat the test in full where there is insufficient
evidence to show that a system has been satisfactorily maintained under
pressure when left filled with medical air for the interim period.

15.96 The most distant terminal unit on each branch must be tested with a
membrane filter at a flow not less than 150 l/min for 30 seconds. The filter
must be free from visible particles when viewed in good light. A suitable test
device is described in Appendix D. All other terminal units should be purged.

156


Table 24 Summary for quality tests for medical gases pipeline systems

Test Gas Paragraph Specification Test result

Particulates All 15.95 Practically free Practically free from visible
from visible particles on
particles in 75 l membrane
sample filter 1

Pipeline Oxygen and 15.105 None 4 No odour
odour medical air
and surgical
air

Water All 15.99 115 VPM 5 H2O
0.095 mg/l detection
(equivalent to tube
dewpoint –40ºC satisfactory 2

at atmospheric
pressure)

Oil Medical air 15.97 Oil content Oil
400 kPa droplet and detection
Surgical air mist tube
700 kPa Oil vapour satisfactory
Oxygen supplied <5 ppm 3
from PSA plant

CO Medical air 15.101 Gas
400 kPa 5 ppm v/v detection
Surgical air tube
700 kPa satisfactory
Oxygen supplied
from PSA plant

CO2 Medical air 15.102 Gas
400 kPa <500 ppm v/v detection
Surgical air tube
700 kPa satisfactory
Oxygen supplied
from PSA plant <300 ppm v/v

NOTES:
1. Typically 40 µm is limit of resolution of human eye.
2. Hydrometer may be used instead of H2O detector tubes.
3. A large sample is required to detect these levels (at least 2 hours running).
4. Odour threshold for particulate material is approximately 0.3 mg/m3.
5. The current moisture specification for oxygen is 60 vpm, the proposed Ph Eur for O2/air and N2O is 50 vpm.

Testing on-site cannot be as accurate as testing under manufacturing conditions.

157


Oil

15.97 A representative sample of all terminal units on medical compressed air
systems and oxygen concentrator systems supplied by compressor plant must
be checked to ensure freedom from odour or oil.

15.98 The most distant terminal unit on the index pipe run and plant test The compressor plant must only be
point must be tested for the total oil content. Oil may be present as liquid, used to supply medical air systems
aerosol or vapour, and an appropriate test device is described in Appendix E. and vacuum systems for test purposes
The total oil content should be in accordance with Table 24. This test must
also be carried out at a test point on the compressor system and oxygen
concentrator system. It is desirable to carry out this test at a plant test point
before any pipeline system is supplied by that plant, to prevent
contamination of the pipeline distribution system. Care should be taken in
selecting the test point, to ensure a representative sample.

Water

15.99 This test is intended to identify contamination of the pipeline system by
moisture. It should not be confused with the test for compressor plant dryer
performance, although it may indicate a failure in the dryer system.

15.100 The plant test point and a representative sample of terminal units
distributed throughout the pipeline systems should be tested for total water
content. The water content must not exceed 115 vpm. The typical water
content of medical gas cylinders is normally below 5 vpm. This may be
measured using the appropriate test device described in Appendix E.

Carbon monoxide

15.101 The most distant terminal units on each branch of a medical air
pipeline system supplied from a compressor plant and PSA systems must be
tested for carbon monoxide, although it would not normally be necessary to
test more than five terminal units. The concentration of carbon monoxide
should not exceed 5 ppm v/v. This may be measured at up to five terminal
units in each system using the appropriate test devices described in
Appendix E.

Carbon dioxide

15.102 The most distant terminal unit on each branch of a medical air
pipeline system supplied from a compressor or an oxygen concentrated plant
must be tested for carbon dioxide. The concentration of carbon dioxide must
not exceed 500 ppm v/v for oxygen from an oxygen concentrator plant.

15.103 Carbon dioxide must not be used as the inert gas shield during
brazing.

Nitrogen

15.104 Nitrogen is used as the inert gas shield, and all terminal units, should
be tested to ensure that the systems have been adequately purged. For oxygen
systems and nitrous oxide/oxygen, an oxygen analyser must be used to ensure
that the oxygen concentration is not less than that given in Tables 24 or 25.
For nitrous oxide systems, nitrogen has been used as the inert gas, and an
instrument based on thermal conductivity, or an infra-red meter, must be used
to check that the system has been adequately purged at every terminal unit.

158


Pipeline odour

Certain plastic materials currently in 15.105 This test must be carried out as the final test. A representative
use will release small quantities of sample of terminal units on all systems must be checked to ensure that there
volatile organic matter into the gas is no taste or odour. This check is performed to ensure that no contamination
stream throughout their life, for has occurred, for example by oil or sealants, burned plastic pipe caps, etc. This
example, flexible hose assemblies, test must not be carried out on nitrous oxide or nitrous oxide/oxygen systems
pendant assemblies, etc. Research has unless filled with medical air test gas. On nitric oxide systems, this test can be
indicated that the quantities released performed using nitrogen from the purge cylinder.
are of no toxicological significance

Gas identification

15.106 The identity of the gas must be tested at every terminal on all
MGPS. This would include all new terminal units, whether on a new
installation or a modification or extension, and a representative sample of
terminal units on an existing system which may have been affected by the
work. All systems must have been filled with the specific gas according to
paragraph 15.86. During the test, do not connect any system to medical
equipment.

15.107 The composition of all compressed gases must be positively
identified. This can be accomplished using an oxygen analyser for oxygen,
nitrous oxide/oxygen and air, and a thermal conductivity or infra-red meter for
nitrous oxide.

15.108 A sampling procedure must be used which will minimise pollution
from nitric oxide, nitrous oxide and nitrous oxide/oxygen mixture.

15.109 The nominal gas concentration at the specific terminal units is given
in Table 25.

15.110 Vacuum must be identified by observation of suction at the
terminal units.

Table 25 Gas concentrations for identification purposes

Medical gas Oxygen concentration Nitrous oxide concentration
% v/v % v/v

O2 minimum 99.0 n/a

Medical and
surgical air 21.0 +/– 1.0 n/a

N2O 0 minimum 98.0

N2O/O2 50%/50% 50.0 +/– 2.0 50.0 +/– 2.0

Notes:
1. The tolerance of the measuring instrument should be allowed in
addition.
2. For oxygen concentrator plant (PSA) supplied system, the minimum
concentration must be 94% oxygen.
3. For bulk liquid/liquid or gaseous cylinder supplied systems, this must be
in accordance with the European Pharmacopoeia (Ph Eur)
requirements.
NOTE: 93% was the suggested EP figure when considering specification.

159


Requirements before a MGPS is taken into use

General

15.111 Before a system is used, the appropriate persons must certify in
writing that the tests and procedures required in paragraphs 15.37–15.78 and
15.86–15.110 have been completed, and that all systems comply with the
requirements. This must include certification that all drawings and manuals
required by the contract have been supplied and “as-fitted” drawings are
correct.

15.112 It must be verified that the AVSUs and the warning systems have
been labelled in accordance with the contract specification and are labelled (or
will be labelled prior to formal use) in a secure manner to state where they
serve.

15.113 All certificates must be dated and signed by the appropriate
witnesses, by the contract supervising officer and by the representative of the
contractor.

15.114 For modifications or extensions to existing systems, the performance
tests for flow and pressure drop (as described in paragraph 15.68) must be
carried out on the completed system using the working gas. If the
performance is in accordance with the specification prepared (as described in
paragraphs 15.29–15.36), the system may be taken into use, provided that all
the other tests have been satisfactorily completed.

Operational policy

15.115 A procedure must be available in accordance with the ‘Operational
management’ volume of this HTM, and must ensure continuity of supply of
cylinders and bulk liquid. This will incorporate a procedure for recording
delivery, handling and storage of full and empty cylinders, with an indication of
who is responsible for these activities. the composition of the cylinder contents
must be certified by the supplier. All deliveries of bulk liquid oxygen should be
tested for conformance to the product licence specification before despatch by
the supplier, and should be supplied with a certificate indicating compliance.

Cylinder storage and handling

15.116 There should be recorded visual checks for correct labelling, including
batch numbers. See the ‘Operational management’ volume of this HTM.

Removal of construction labels

15.117 When all tests have been completed satisfactorily, the construction
labels which were fixed to the terminal units should be removed on the
authority of the authorised person (MGPS).

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Anaesthetic gas scavenging systems

General

15.118 BS 6834:1992 specifies the tests to be carried out on AGS systems
which comply with the British Standard. The tests specified are performance
tests, to ensure that the system performs in accordance with the design
specification and safety tests, to ensure that the safety criteria are met.

15.119 Systems which do not comply with the British Standard should also
be tested to ascertain their performance and to ensure that the criteria for
patient safety can be achieved.

15.120 The tests for performance and safety criteria are described in this
Chapter. It is recommended that all AGSS are tested at commissioning and
that the tests are repeated yearly, or more frequently if there is reason to
suspect that the performance of the system is not satisfactory. Monitoring
staff exposure to anaesthetic gases is recommended in the ‘Operational
management’ volume of this HTM in order to comply with the requirements
of COSHH. The results of such monitoring will identify potential inadequacies
in the AGSS, which should then be tested to ascertain its performance.

15.121 The responsibility for the tests should be clearly identified at the
contract stage for new installations, in the same way as for the MGPS. In
general, the contractor should carry out the tests, which should be witnessed
by the authorised person (MGPS). It is unlikely that each health authority or
trust can justify the purchase of the specialist equipment required to carry out
these tests, unless there are a significant number of AGSS installed on the
site.

15.122 The general requirements set out in this volume for validation and
verification should be followed, including tests for cross-connection and
mechanical function of terminal units.

Performance tests: disposal systems

Powered device

15.123 All equipment should be tested to ensure that it performs
satisfactorily during continuous operation under full load for one hour.

15.124 All electrically-powered equipment should be tested as follows:

a. check for correct rotation;

b. check the current through the powered device at full load;

c. check the insulation resistance and the effectiveness of the earthing of
all electrical items.

Pipework/ductwork installation

15.125 The procedure set out in Appendix D ,Section D2 of BS 6834:1987
should be followed.

15.126 Where the AGSS is installed with other medical gases systems,
it should be included in the cross-connection tests as specified in
paragraph 15.58.

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Performance testing

15.127 The disposal system should be tested to ensure that it meets the Developments in oxygen standards
following requirements, regardless of the number of terminal units on the may result in reduced extract flows for
system: systems in the future

Pressure drop Extraction flow

1 kPa Maximum 130 l/min
4 kPa Minimum 80 l/min

15.128 These criteria should be met, regardless of the number of receiving
systems connected to the disposal system.

15.129 The test should be carried out as described in Appendix K of
BS 6834:1987 (1992). Where a disposal system is designed to operate with
more than one terminal unit, that is, more than one receiving system in use
simultaneously, the test should demonstrate that the above criteria can be met
under all conditions, that is, with one or all of the terminal units in use.

15.130 The test device should therefore first be inserted into each terminal
unit in turn, with all other terminal units closed. The test should be repeated
with all other terminal units open and in use. Ideally, this would mean inserting
a test device into every terminal unit on the system and checking at each
terminal unit in turn that the required criteria are met. In practice, it is
sufficient to connect a receiving system conforming to BS 6834:1987 (1992)
to every terminal unit, and to then check each terminal unit in turn.

15.131 The contractor should provide a certificate giving details of the
performance of the system.

Receiving system

15.132 The induced flow into the receiving system by the disposal system
should be tested at every receiving system, to ensure that the induced flow
does not exceed 0.5 l/min.

15.133 The procedure and the test equipment required are described in
Appendix F of BS 6834:1987 (1992).

Performance efficiency

15.134 The method of testing for performance is set out in Appendix G of
BS 6834:1987 (1992). The specific challenge gas flow, comprising a mixture of
oxygen and nitrous oxide, is introduced into the receiving system to simulate
the gas flow from the breathing circuit via the transfer system.

15.135 It should not be possible to detect any nitrous oxide in the vicinity of
the receiving system when the system is challenged in this way.

15.136 This test is difficult to carry out under site conditions, since it is not
easy to set up the correct challenge flow and the ambient conditions will affect
the results. This test should be carried out under laboratory conditions by the
manufacturer of the receiving system and a certificate should be provided in
accordance with BS 6834:1987 (1992).

162


15.137 It may be necessary to carry out an assessment of the performance
of an existing scavenging system which does not comply with BS 6834:1987
(1992). In this case, the test procedure set out in the British Standard should
be followed as far as possible.

15.138 The operation of flow indicators, power-on indicators and alarm
systems should also be checked.

15.139 For the purposes of diversity it may be assumed that in any
operating department, one receiving system for each operating suite is in use
at any time.

Methods and procedures for validation and
verification of medical gas pipeline systems

General

15.140 The procedure given here is an example only. Other procedures
may be used, but validation of the test method should be documented.

15.141 The sequence of tests in this procedure is important and should be
followed.

15.142 The general requirements of paragraphs 15.17–15.36 must be
observed.

15.143 All tests will need to be planned and carried out by the appropriate
persons.

15.144 Forward planning will be necessary to ensure that the necessary
persons and test equipment will be available.

15.145 Summaries of the tests required on the pipeline carcass and on the
total pipeline system are given in Tables 22 and 23.

Labelling and marking

15.146 Inspect each pipeline carcass to ensure that the pipelines and the
AVSUs are labelled in accordance with the contract specification, and BS 1710
and that the terminal unit base blocks are marked in accordance with
BS 5682:1984.

15.147 If the labelling and marking is correct, complete Form B1.

Sleeving and supports

15.148 Inspect each pipeline carcass to ensure that the pipelines are
sleeved and supported in accordance with the contract specification.

15.149 If the sleeving and supports are correct, complete Form B1.

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Table 26 Summary of tests required on pipeline carcass

Test order Description Form

1 Labelling and marking B1
2 Sleeving and supports B1
3 Leakage B1
4 Cross-connection B2

Table 27 Summary of tests required on pipeline system

Test order Description
Form

5 Leakage from total compressed into total vacuum B3
system
6 Leakage into total vacuum system B4
7 Closure of AVSU B5A
8 Zoning of AVSU B5B
9 Cross-connection B6
10 Flow and pressure drop at terminal units B7
11 Mechanical function of terminal units B7
12 Gas specifity of terminal units B7
13 NIST connectors B7
14 Performance tests of the pipeline sysem B7
15 Functional tests of supply system B8
16 Pressure safety valves B9
17 Warning systems B10
18 Verification of drawings B11
19 Filling with medical air B12
20 Purging and filling with specific gases B13
21 Quality B14
22 Gas identity B15

Leakage

15.150 If it has been necessary to link the carcasses to form a single system
for the purpose of this test, care must be taken to ensure the links are
removed. Alternatively, the test may be carried out on sections of the pipeline,
provided no part of the pipeline is omitted.

General conditions

15.151 The pipeline should be completely installed and correctly supported.
The base blocks of all terminal units should be fitted and blanked. Other
devices such as safety valves or pressure sensors need not be fitted. All
connection sockets for such devices should be blanked.

Procedure

15.152 Connect a suitable pressure measuring device to the pipeline. Fill the
pipeline with test gas at the specified test pressure. Disconnect and remove the
gas supply. Record the pipeline pressure and room temperature initially and
again at the end of the test period (2–24 hours).

164


Results

15.153 The rate of pressure drop during the tests should be less than
0.025% per hour, except for pressure changes due to temperature variations.
The pressure change due to temperature variation is approximately 0.35%
per ºC. Record the results on Form B1.

Cross-connection

15.154 Any links between the systems should be removed before this test
is carried out. All pipelines should be at atmospheric pressure and all AVSUs
should be open. A single pressure source should be used and connected to
one pipeline at a time. This should remain under pressure throughout the test.
At least one base block on all other pipelines should be fully open.

Procedure

15.155 Connect one pipeline to the pressure source. Check that no gas
flows from the open-base block on the other pipelines which are not under
pressure. Each terminal unit on the pipeline under test should be opened,
checked for flow and then reblanked. When testing has been completed on
one pipeline, the pressure source should be removed and that pipeline should
be left open to atmosphere. Another pipeline should then be pressurised and
the procedure repeated.

Results

15.156 The contractor should record that satisfactory tests have been
completed on Form B2.

Leakage from compressed medical gas systems

15.157 The leakage test described above should have been completed
satisfactorily. All terminal unit valves and other devices such as safety valves
and pressure sensors should be fitted. The supply system should be isolated
from the pipeline. there should be no links between the pipeline systems.
The test may be carried out on sections of each pipeline, provided no section
is omitted. Different sections and pipelines may be tested at the same time.

Procedure

15.158 Connect a suitable pressure measuring device to the pipeline.
Fill the pipeline (or section of pipeline) with test gas at pipeline distribution
pressure. This filling procedure may also be used to measure the volume of
the pipeline (see Appendix H). Disconnect and remove the gas supply. Note
the pressure and temperature initially and again at the end of the test period.

Results

15.159 The rate of pressure drop during the test period should not exceed
the value specified in Table 23, after allowing for pressure changes due to
temperature variation. Record the results on Form B3.

165


Leakage into vacuum systems

15.160 The leakage test described above should have been completed
satisfactorily. All terminal unit valves and other devices, such as pressure
sensors, should be fitted. The vacuum supply should be connected to the
system under test.

Procedure

15.161 Connect a vacuum gauge to the system. Run the vacuum supply
system to maintain pipeline distribution pressure until the pipeline system is
dried out. With the system at pipeline distribution pressure, isolate the vacuum
supply system. Note the vacuum initially and again after one hour.

Results

15.162 Record the results on Form B4. The pressure increase after one hour
should not exceed 10 kPa. There is no additional allowance for temperature
variation in this test.

Closure of AVSUs

15.163 The test specified in paragraphs 15.50–15.53 must have been
completed satisfactorily.

Procedure

15.164 The procedure for this test is as follows:

a. connect a pressure-measuring device to the system. The system should
be at pipeline distribution pressure, with all AVSUs closed;

b. depressurise the pipeline downstream of all AVSUs by inserting and
leaving an open probe or flow meter into downstream terminal units.

Results

15.165 Record the results on Form B5A. There should be no pressure or
vacuum decrease upstream of the valve under test.

Zoning of AVSUs

15.166 The tests specified in paragraphs 15.54–15.57 must have been
completed satisfactorily.

Procedure

15.167 The procedure for the test is as follows:

a. connect a pressure-measuring device to the system. The system should
be at pipeline distribution pressure, and all AVSUs except the one
under test should be open;
b. decrease the pressure in the pipeline downstream of the AVSU under
test to about 1 bar g (or 200 mm Hg (27 kPa) for vacuum). Note the
number of terminal units controlled by the AVSU and check that they
are all at the test pressure of 1 bar g (or 200 mm Hg (27 kPa));

166


c. as test probes are inserted into terminal units in the section under test,
there may be loss of pressure or vacuum. If necessary, re-adjust the test
pressure;

d. check the AVSU for leakage into the environment.

Results

15.168 Record the results on Form B5B. Open the AVSU to achieve
pipeline distribution pressure and proceed to test the next AVSU.

15.169 During the test, it will be necessary to have the supply system
connected to maintain pressures.

Cross-connection

15.170 These tests should be carried out on one pipeline at a time. All
pipelines should be at atmospheric pressure and AVSUs should be open.
A single-pressure source should be used and connected to one pipeline at a
time, which should remain under pressure throughout the test.

Procedure

15.171 The procedure is as follows:

a. connect one pipeline to the pressure source at pipeline distribution
pressure;

b. in order to depressurise the other system, insert an open probe into
one terminal unit on each other system. Check that no gas flows into
or out of these probes;

c. check that gas flows through every terminal unit of the pipeline under
pressure;

d. check that there is no gas flow from any other terminal units when
they are opened with the correct probes.

Results

15.172 Record the results on Form B6 if there are no cross-connections.

15.173 Repeat the procedure described above on each pipeline in turn,
including vacuum, preferably at one session. This test should be repeated in
full if any subsequent modifications are made to the pipeline system during
construction.

Functional tests of terminal units

15.174 These tests may be carried out at the same time as the cross-
connection test described above. In this case, only one system at a time is
pressurised.

Procedure


a. before commencing the tests, check that the test equipment meets the
requirements given in Appendix C for the system under test. All
terminal units should be complete with the fascia plate;
167


b. insert the test device described in Appendix C into each terminal unit in
turn on the system under test. Note that the pressure drop at the
specified flow does not exceed the value given in paragraph 15.63;

c. check that the gas-specific probe can be inserted, captured and
released and that it does not swivel in horizontally-mounted terminal
units, and that it can swivel without undue force in vertically-mounted
terminal units;

d. check that no gas is released at each terminal unit by the probes for all
other gases used, and that no probes can be engaged;

e. check that all NIST connectors accept the NIST probe for the correct NISTs incorporated in certified
gas, and that mechanical connection is made. Check that the NIST assemblies do not need to be tested
probes for all other gases do not make mechanical connection; (see paragraph 15.67)

f. note that the NIST self-sealing device functions as specified in
paragraph 15.67.

Results

15.175 Record the results on Form B7, if they are in accordance with
paragraphs 15.63–15.67.

Performance tests of the pipeline system

15.176 These tests should be carried out on one system at a time.

15.177 All AVSUs should be open. Connect a supply of test gas at the supply
source of sufficient capacity to meet the total design flow of the system. The
vacuum supply system may be used to test the vacuum pipeline system, as
described in Appendix G.

Procedure

15.178 The procedure is as follows: Remedial work may be needed if
these specifications are not met
a. insert leaks into selected terminal units, AVSUs and NISTs as
appropriate throughout the system under test, to provide a total
flow equal to the total design flow of that system;

b. run the system so that the pressure/vacuum at the source meets the
specification given in column 6 of Table 23;

c. check the gauge pressure at the specified flow (Table 4) at selected
terminal units throughout the system;

d. record the results on Form B8 if they are in accordance with paragraph
15.68.

Supply system tests

General

15.179 All supply systems should be installed and connected to normal and
standby power supplies.

15.180 Specific checklists should have been prepared for each item of plant
in accordance with paragraph 15.72.

168


Procedure


a. the functions and operating parameters of each item of plant should be
checked;

b. the supply systems should be shown to operate on the essential power
supply;

c. all pipework joints should be tested for leakage at normal operating
pressure;

d. the compressor plant should be tested for leaks during normal running.

Results

15.182 It should be confirmed that the manufacturer's specification meets
the requirements of the contract specification.

15.183 Record the results on Form B9, if they are in accordance with the
specific checklist.

Safety valve inspection

15.184 Tests of safety valves are not required.

Procedure


a. inspect each safety valve to check that the discharge capacity and the
set pressure are in accordance with the contract specification;

b. check that the safety valves conform to BS 6759:Part 2;

c. inspect the certification supplied with each valve.

Results

15.186 Record the results on Form B10 if they are in accordance with
paragraph 15.72.

Warning system tests

General

15.187 The tests should be carried out for one function at a time on one
system at a time.

15.188 All alarm systems should be fully installed and in operation.

Procedure


a. adjust the pressure in each pipeline system either locally or throughout
the pipeline system;

169


b. observe that the appropriate changes in warning-system conditions
occur in accordance with paragraphs 15.76 and 15.77;

c. check that the warning system will operate from the essential power
source.

Results

paragraphs 15.76 and 15.77.

Verification of drawings

Procedure

15.191 Inspect the “as-fitted” drawings, to ensure that all variations from the
contract drawings have been recorded.

Results

15.192 Record the results on Form B12, if the drawings are in accordance
with paragraph 15.78.

Filling with medical air

15.193 When an indefinite period may elapse before the system is taken into
use, it should first be tested for particulate contamination, using medical air, as
the test gas, in accordance with paragraphs 15.79–15.85.

Procedure

15.194 The procedure in paragraphs 15.79–15.85 should be followed for the
particulate contamination test only, in accordance with paragraphs 15.95 and
15.96. If the test is satisfactory, the system should be filled with medical air
and left pressurised at pipeline distribution pressure.

Results

15.195 If the results are satisfactory, they should be recorded on Form B14,
which should be annotated to indicate that the system has been tested with
medical air.

Special connectors

15.196 At the end of the contract period, the contractor should ensure that
any special connectors are removed from site.

Purging and filling with specific gas

General

15.197 The following should be carried out prior to purging and filling with
the specific gas (all systems may be filled with their specific gases at the same
time):

170


a. all previous tests should have been satisfactorily completed;

b. each pipeline system should be connected to its source of supply, with
all AVSUs open;

c. all sources of test gas should be disconnected;

d. all special connectors and cylinders should be removed from site.

Procedure


a. starting at atmospheric pressure (except for vacuum systems), fill each
pipeline system to pipeline-distribution pressure;

b. with the supply system on, purge each terminal unit with a known
volume of gas at least equal to the volume of the pipeline being tested;

c. leave each system at pipeline-distribution pressure, with the supply
system connected.

Results

15.199 Record on Form B13 that the systems have been filled in
accordance with paragraph 15.86.

Tests for quality

15.200 The pipeline systems should be at pipeline-distribution pressure and
filled with the specific gas, except for tests for particulate contamination,
which may be carried out with medical air if the system is not to be taken into
use immediately.

Procedure


a. the tests specified in paragraphs 15.88–15.105 should be carried out
on a representative sample of terminal units for each system, at the
discretion of the QC. The sample should include as a minimum the
most distant terminal unit on each branch, which would normally be
the first terminal unit to be tested. Depending on the results of the
tests, the QC should decide the number and location of additional
terminal units to be tested;

b. tests may be carried out simultaneously where appropriate;

c. the tests are summarised in Table 24.

Results

15.202 Record the results on Form B14 if they are in accordance with the
specifications of paragraphs 15.88–15.105.

171


Tests for gas identity

General

15.203 All systems should preferably be tested at the same time. The
previous tests must have been satisfactorily completed.

Procedure

15.204 The tests specified in paragraphs 15.106–15.110 should be carried
out at all terminal units, using the equipment described in Appendix F.

Results

paragraphs 15.106–15.110 and Table 25.

System taken into use

15.206 When all the tests have been satisfactorily completed, the
construction labels should be removed and the system may be taken into use.

172

Appendix A

Testing, commission and filling for use: forms to be completed during testing and
commissioning of piped medical gases systems

Form

Summary of tests B0

Carcass tests
Labelling and marking B1
Sleeving and supports B1
Leakage test B1
Cross-connection test B2

System tests
Leakage test B3
Vacuum leakage test B4
AVSUs – closure and zoning tests B5
Cross-connection test B6
Functional tests of terminal units
and NIST connectors B7
Design flow performance test B8
Sources of supply B9
Pressure safety valves B10
Warning systems B11
Verification of drawings B12
Purging and filling B13
Quality B14
Gas identification B15

173

Appendix B

Gas pressure variation with temperature

General

1. Tests are specified for leakage of the pipeline carcass and the pipeline
systems. During these tests, pressure changes may occur which are caused by
temperature changes rather than leakage.

2. Pressure changes due to temperature difference may be calculated
according to the Gas Laws.

3. It is assumed that the temperature in the pipeline is uniform in all
branches. If substantial runs are external, an average temperature should be
chosen.

Calculation

4. The change in gas pressure with temperature is as follows.

5. P1/T2 = P2/T2 where P1 and P2 are the initial and final absolute pressure
of a fixed volume of gas and T1 and T2 are the initial and final absolute
temperatures.

6. (bar absolute) and Kelvin
Therefore P2 = P1 x T2

T1

7. Care must be taken to express pressure and temperature in absolute
values.

8. Pressure is normally expressed in gauge pressure. Absolute pressure =
gauge pressure + atmospheric pressure.

9. Temperature is normally expressed in ºC.

Examples

10. The carcass of a medical air pipeline is tested for leakage at a working
pressure of 14.0 bar gauge pressure. The temperature is 13ºC at the
beginning of the test and 17ºC at the end of the test.

P1 = 14.0 + 1.0 = 15.0 bar a

T1 = 273 + 13 = 286K

T2 = 273 + 17 + 290K

therefore P2 = 15 x 290 = 15.21 bar (absolute)
286 (14.21 bar g)

that is, gauge pressure should read 14.21 bar at the end of the test, assuming
that no leakage has occurred.

191

Appendix C

Pressure drop test device

General

1. Special test devices are required to measure the pressure at specified
flows at each terminal unit.

2. Suitable test devices are commercially available or may be constructed
in accordance with the outline specification given below.

Measurement principle

3. Flow at a specified pressure may be measured either with a calibrated
orifice or with a flowmeter.

4. Pressure may be measured with a bourdon gauge.

5. A gas-specific probe conforming to BS 5682 should be used to connect
the device to the terminal unit.

6. The test device is connected to the terminal unit by the gas-specific
probe and the pressure at the specified flow is read on the gauge.

Functional requirements

7. The test device should consist of the following components:

Gas-specific Body on/off Orifice
probe to valve or
BS 5682 (optional) flowmeter

Pressure
gauge

8. The body may be of a design which allows exchange of the following
components:

a. gas-specific probes;

b. calibrated orifices;

c. pressure gauges.

9. An on/off valve may be incorporated into the body.

10. The complete assembly should be tested for leaks.

11. Where it would be impractical to use gas-specific probes, it is
permissible to use a specially designed universal probe, provided it is impossible
for such a probe to be improperly used on medical equipment.
The special probe should be clearly marked “test only”.

192

Appendix C

Test probes for gas specificity

12. The gas-specific probe for each service should be as specified in
BS 5682:1984.

Orifices

13. The orifices should be selected from the information on the
manufacturer’s data sheets or from practical testing.

14. These devices should be checked against a flowmeter before use.

Flowmeter

15. A bobbin flowmeter calibrated to a flow of 40 l/min may be used to
measure flow under vacuum.

Pressure gauge

16. A 50 mm bourdon gauge with an appropriate full scale reading and
interval should be used as follows:

Test pressure kPa Scale Scale interval

400 0–7 bar 0.1 bar
700 0–11 bar 0.5 bar
Vacuum 0–760 mm Hg 50 mm Hg
(0–100 kPa) (5 kPa)

Note: 1 bar = 100 kPa approx.

193

Appendix D

Membrane filter test device

General

1. The function of this test device is to collect particulate material which
may be present in the pipeline.

2. The terminal units to be sampled should be in accordance with
paragraph 15.91.

3. Filter holders appropriate to the pressure encountered are commercially
available.

4. The filter holder should be specified for use at pipeline-distribution
pressure and be oxygen-compatible.


5. A known volume of gas is passed through a membrane filter which will
collect all visible particles.

6. Membrane filters are available in a range of pore sizes. A maximum
pore size of 10 mm will collect all visible material. Pore sizes below 0.2 mm are
likely to restrict flow; typical pore size is 0.45 mm.

7. The QC should examine the condition of the filter, which should be
practically free from visible particles, and should decide whether the test has
passed or failed, according to the number and size of visible particles.

Test equipment

8. The following equipment is required:

a. a membrane filter holder;

b. a supply of white membrane filters of not more than 10 µm pore size
and with high mechanical strength;

c. a means of connecting the filter to the pipeline;

d. a means of controlling the flow through the filter, which is connected
downstream of the filter. One method of achieving this is to use the
appropriate Amal jets to achieve a flow of 150 l/min at 400 kPa and
700 kPa;

e. all equipment must be oxygen-compatible and hoses should be anti-
static.

Procedure

9. The following procedure should be carried out:

a. place a single filter into the filter holder;

194

Appendix D

b. assemble the filter holder so that it seals;

c. set the flow controller to 150 l/min;

d. connect the filter holder to the terminal unit for 30 seconds;

e. inspect the filter. Evaluate and record the result.

195

Appendix E

Equipment for contaminant testing

General

1. The function of these tests is to establish whether the pipeline has been
contaminated during construction or modification. The specifications for the
permissible concentrations of each component are summarised in
Table 24.

2. Simple equipment which is of the required sensitivity and is suitable for
use on site is commercially available.


3. A known volume of gas is passed through a tube packed with an
absorbent, which is coated with specific colorimetric reagents. The reagents
react quantitatively with the compound to be measured and produce a colour
change along the length of the tube, which is proportional to the
concentration of the compound being measured.

4. Tubes are available with appropriate sensitivities for the measurement
of oil, water, carbon monoxide and carbon dioxide, sulphur dioxide, and
higher oxides of nitrogen.

Procedure

5. It is possible to measure water, carbon monoxide and carbon dioxide
simultaneously by connecting a tube and pump for each contaminant to a
common hose, which is connected to the pipeline at a flow of 2 to 5 l/min.
The pump is used to draw a known volume of gas through the tube at
ambient pressure (the gas being tested should be allowed to escape freely to a
safe area), and allow evaluation of the concentration of the compound being
measured.

6. There are tubes currently available to measure oil contamination, but
each test takes a minimum of 120 minutes.

7. These tubes give a quantitative response and are not intended for re-
use. It may be appropriate if a nil reading is recorded, to validate that the tube
is functional by testing the tube on a known sample.

8. Record the results. Non agent-specific detector tubes are
difficult to interpret and are not
recommended because of their
qualitative and not quantitative
response

196

Appendix F

Equipment for gas identification

General

1. The function of these tests is positively to identify medical gases by
measuring their oxygen, nitrous oxide and nitric oxide content. The specified
concentration limits for this purpose are given in Table 25.

N2 should be used as the inert gas 2. Portable equipment of the required specificity and sensitivity is
shield; carbon dioxide should not be commercially available.
used
3. Thermal conductivity meters do not give a positive identification of
nitrous oxide in the presence of carbon dioxide, and should not be used as a
sole means of identification of nitrous oxide. A specific nitrous oxide meter
should be used. If carbon dioxide pipelines are present, for example in IVF
clinics, a carbon dioxide detector tube should be used.

Specificity

Oxygen

A paramagnetic meter is the specified 4. Oxygen-specific sensors using different measurement principles are
instrument for identity of oxygen currently in manufacture. The oxygen sensor should not give greater than
±1% response in the presence of 100% nitrous oxide, 100% nitrogen or
100% carbon dioxide. Nitrous oxide and nitric oxide could be present at up to
100% concentrations if the system has been inadequately purged.

Nitrous oxide

5. The nitrous oxide sensor should not give greater than ±1% response in
the presence of 100% oxygen, 100% nitrogen or 100% carbon dioxide. An
infra-red/fuel cell meter is now commercially available.

Specification

6. The equipment should be portable, preferably battery-powered, with
digital or analogue indication of 0–100% to one decimal place. The battery
should give at least eight hours’ continuous running between recharging or
replacement.

7. An accuracy better than ±1% is required, with a zero stability of 2.5%
per day.

8. The response time must be not more than 15 seconds to 90% of the
final reading.

197

Appendix F

Procedure

9. This is as follows:

a. calibrate the equipment to check zero and 100% response;

b. regulate the flow of gas from the terminal unit to the equipment;

c. allow the reading to stabilise;

d. record the result for each terminal unit.

198

Appendix G

Procedures for measuring the design flow of vacuum
plant

General

1. A method is described which enables a large vacuum system to be run
at the system design flow, using a minimum quantity of calibrated test
equipment.

Measuring principle

2. A calibrated orifice device is connected to the system close to the plant
so that the plant runs at the system design flow. The vacuum at that point is
then noted.

3. The calibrated orifice is then removed and a number of uncalibrated
leaks are introduced throughout the system to give the same level of vacuum
at the plant.

Test equipment

4. Suitable calibrated orifice devices are available.

5. Uncalibrated leaks may be constructed from medical gas probes
connected to large AMAL jets or lengths of suitable diameter tubing.

Procedure

6. Connect the air flow meter at a suitable point adjacent to the plant.
Set the meter orifice to the system design flow.

7. Run the plant continuously with the pipeline system isolated.

8. Record the pressure on the vacuum gauge.

9. Reconnect the pipeline system to the plant. Close the meter orifices,
leaving the vacuum gauge connected.

10. Insert non-calibrated leaks at suitable points throughout the pipeline
system.

11. Adjust the number and size of the non-calibrated leaks until the
vacuum gauge at the test point shows the same reading as in paragraph 8
above.

12. The system will then be running at the system design flow and the
total system test can be carried out at each terminal unit for performance.

199

Appendix H

Procedure for measuring pipeline volume

General

1. A method is described to measure the volume of a compressed medical
gas system with an acceptable accuracy.


2. A known volume of gas is delivered into a closed system from a
cylinder. The pressure changes in the system and the cylinder are noted. Since
the volume of the cylinder is known, the volume of the pipeline system can be
calculated.

3. The accuracy of the method depends upon the accuracy of reading the
pressure changes.

Test equipment

4. The following equipment is required:

a. a cylinder of test gas of known internal volume (water capacity). This is
not the volume of gas contained in the cylinder. To achieve maximum
accuracy it is essential to arrange for the maximum change in pressure.
In practice, the cylinder used to charge the system for this test should
be the smallest practicable to fill the pipeline to the operating pressure;

b. a cylinder pressure regulator fitted with an accurate gauge to measure
cylinder pressure. A gauge of at least 100 mm diameter with an
appropriate full-scale reading is required;
c. an accurate (100 mm) gauge to measure pipeline pressure. This gauge
should be calibrated in the same units as the cylinder pressure gauge;

d. a means of connecting the cylinder to the pipeline.

Procedure

5. Establish the water capacity of the cylinder of test gas (medical air or
nitrogen).

6. Fit the regulator onto the cylinder and read the pressure on the gauge.

7. Connect the pipeline pressure gauge to the pipeline and bleed the
pipeline to zero gauge pressure.

8. Connect the cylinder to the pipeline and allow test gas to flow slowly
into the pipeline up to pipeline distribution pressure. Turn off the cylinder
valve. Allow the system to equilibrate for a few minutes.

9. Read the pipeline pressure gauge and the cylinder pressure gauge.

200

Appendix H

10. The volume of the pipeline may be calculated as follows:

Pipeline volume = cylinder volume x change in cylinder pressure
change in pipeline pressure

P1V1 + P2V2 = P3V1 + P4V2

V1(P1 – P3) = V2 (P4 – P2)

therefore

V2 = V1 (P1 – P3)

(P4 – P2)

where

V1 = cylinder volume
V2 = pipeline volume
P1 = initial cylinder gauge pressure
P3 = final cylinder gauge pressure
P2 = initial pipeline gauge pressure
P4 = final pipeline gauge pressure

11. The volume (water content) of a G-size medical air cylinder may be
taken as 23.3 litres. The volume (water content) of a J-size medical air cylinder
may be taken as 46.6 litres.

12. To ensure maximum accuracy it is recommended that the system is
vented and refilled 2–3 times and the average result taken.

201

202

Pressure loss data

Appendix J
400 kPa
3000
22mm

2500 22mm
Pressure Loss

7kPa

2000 14kPa
Free air air flow (l/m)

22mm 21kPa
Free flow (l/min)

1500

15mm
1000
15mm

15mm 12mm
12mm
500
12mm

0
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75
Pressure drop (kPa/m)

400 kPa
35000
54mm

30000
Pressure Loss
54mm

7kPa
25000
14kPa

20000 54mm 21kPa
Free flow (l/min)

42mm
42mm
15000

35mm
42mm
10000 35mm

35mm 28mm
28mm
5000
28mm

0
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75

Appendix J
203

204

Appendix J
700 kPa
3500

22mm
22mm
3000

2500 Pressure Loss

22mm 7kPa
Free air flowflow (l/m)

2000 14kPa
Free air (l/min)

34kPa
1500

15mm 15mm
1000
15mm

12mm
12mm 12mm
500

0
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25 3.5 3.75 4 4.25

700 kPa
35000
54mm 54mm

30000
Pressure Loss

54mm
7kPa
25000
14kPa

20000 34kPa
Free flow (l/min)

42mm

42mm
15000 42mm

35mm
35mm
10000
35mm
28mm 28mm
28mm
5000

0
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25 3.5 3.75 4 4.25

Appendix J
205

206

Appendix J
42mm Vacuum at 450 mm Hg (60 kPa)
900

35mm
800

700

28mm
600
Free air flow flow (l/m)

500
Free air (l/min)

400 22mm

300

200
15mm

100
12mm
0
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5 5.75 6 6.25
Note: all lines are applicable to pressure losses of 10 mm Hg, 20 mm Hg, 30 mm Hg and 50 mm Hg (1.3 kPa, 2.7 kPa, 4.0 kPa and 6.7 kPa)

Vacuum at 450 mm Hg (60 kPa)

12000

10000 76mm
(l/m)

8000
Free air flow
Free air flow (l/min)

6000

54mm

4000

42mm

2000

35mm

0
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5 5.75 6 6.25
Note: all lines are applicable to pressure losses of 10 mm Hg, 20 mm Hg, 30 mm Hg and 50 mm Hg (1.3 kPa, 2.7 kPa, 4.0 kPa and 6.7 kPa)

Appendix J
207

Appendix K

Pressure regulations for 400 kPa (medical gases and medical air) and 700 kPa
systems (surgical air)

Pressure regulation for 400 kPa systems (medical gases and medical air)

1. The minimum pressure of 355 kPa which must be available at each
terminal unit is the minimum required for medical equipment, specifically
blenders. The pressure settings of the line regulators are based on achieving
this minimum pressure, taking into account the operating tolerances of the
components.

2. Typical pressure relationships are shown in Figure 21.

3. When designing the pipeline distribution system, the pressure loss
allowance of 10% (including terminal units and hose assemblies) requires a
minimum plant pressure of 420 kPa. The line pressure regulator has a control
tolerance of ±4%; the maximum pressure likely to occur during static
conditions is 460 kPa.

4. The pressure relationships are shown in Figure 21. Pressure regulations
are intended as a guide to illustrate the relationship between the various set
pressures. The actual pressure setting in practice could vary between 460 and
410 kPa depending on the design of the supply and distribution system. It is
important, however, that at the point of use, the minimum pressure is
achieved at the required flow.

5. Existing systems should be checked to ensure that any extension or
modification is compatible with the existing systems.

6. Pressure regulators which require a continuous bleed to control
pressure are not recommended because of the wastage of gas or air.

7. The pressure losses across a terminal unit and across a pendant (which
includes a terminal unit) are shown in Table 1 (Pressure regulation). This is
derived from BS 5682, amendment 5419:1987 and has been modified to
include surgical air with flows at 350 l/min.

Pressure regulation for surgical air 700 kPa systems

8. Compressed air for surgical tools should be available at the terminal
unit at a pressure of 700 kPa at the required maximum flow of 350 l/min.
To avoid over-pressurisation at lower flows, it will be necessary to provide a
pressure control unit upstream of the terminal unit. The pressure loss of the
hose connection between surgical tools and the terminal unit should be taken
into account.

9. When designing the upstream pipeline distribution system, the pipeline
pressure loss allowance of 15% requires a minimum plant/manifold pressure of
approximately 1150 kPa. The line pressure regulator has a control range of
±5%; the maximum pressure likely to occur during static conditions is
therefore approximately 1265 kPa.

208

Appendix K

10. These pressures are approximate; in practice the exact settings will
depend on the design of the supply system and the distribution system. It is
important to achieve the required flow at the minimum pressure at the point
of use; the actual pressure settings which are used to achieve this will vary
with each system design.

Area alarm nominal setting

11. The following statements apply to both 400 kPa and 700 kPa systems.

12. It should be noted that the alarm pressure switch setting and the
safety valve settings overlap. It is not intended that the alarm system should
provide a warning of safety valve relief. The over-pressure alarm is intended to
provide users with advance warning of a potentially hazardous increase in line
pressure which could adversely affect the operation of equipment such as
blenders. Safety valves are intended to provide system protection in the event
of regulator failure.

13. The over-pressure alarm setting should allow the alarm to switch off at
a pressure just above the maximum static pressure in the system.

14. Safety valves to BS 6759 have a specified performance in which the
minimum lift pressure is 97% of the set pressure whilst the full discharge
pressure is 110% of the safety valve set pressure.

15. Air receiver set pressure is 110% of the nominal working pressure.

209

Appendix K

600

580 580

560 Safety valve setting

540

Set pressure 530 kPa

520

510

500

High pressure switch
accuracy +/–4% set pressure
480 480

460 460 460

440 Set pressure 440 kPa Line pressure regulator
tolerance +/–4%
Can vary between
460 and 410
420

Pipeline operating range
400 Allowable pressure loss
420–380 kPa

380
375 at front of terminal unit

360
355

Low level pressure switch
accuracy +/–4% of set pressure
340

Figure 21 Pressure settings for 400 kPa systems

210

References

Acts and Regulations BS 1845: 1984 Specification for filler metals for
brazing.
Public Health Act 1961. The Stationery Office.
BS EN ISO 9000 Quality systems.
Water Resources Act 1991. The Stationery Office.
BS 2871 Specification for copper and copper alloys.
Water Industry Act 1991. The Stationery Office. Tubes.

SI 2169: 1989 Pressure systems and transportable gas BS EN 60898: 1991 Specification for circuit breakers
regulations. The Stationery Office, 1989. for overcurrent protection for household and similar
installations.
SI 3246: 1994 The control of substances hazardous to
health (COSHH) regulations. The Stationery Office, BS 4272 Anaesthetic and analgesic machines.
1994. Part 3 : 1989 Specification for continuous flow
anaesthetic machines.
Medicines Act 1968. The Stationery Office.
BS 4800:1989 (1994) Schedule of paint colours for
Electromagnetic compatibility (89/336/EEC). Official building purposes.
Journal of the European Communities L139 23.5.89.
Amended by 91/263/EEC and 92/5031/EEC BS EN 60947 Specification for low-voltage
switchgear and controlgear.

BS EN 60947-2: 1996 Circuit-breakers.
British Standards
BS 5169: 1992 Specification for fusion welded steel
BS 7671 Requirements for electrical installations. IEE
air receivers.
wiring regulations. 16th edition.

BS 5359: 1976(1983) Specification for magnetic
BS 88 Cartridge fuses for voltages up to and
eleven-disk packs for data processing. Mechanical
including 100V a.c. and 1500 V d.c.
and magnetic properties.
BS 89 Direct acting indication analogue electrical
BS 5378 Safety signs and colours.
measuring instruments and their accessories.
Part 3 : 1982 (1995) Specification for additional
signs to those given in BS 5378: Part 1.
BS EN 132:1991 Respiratory protective devices –
definitions.
BS 5682: 1984 (1992) Specification for terminal units,
hose assemblies and their connectors for use with
BS 341 Transportable gas container valves.
medical gas pipeline systems.
BS 6017: 1981(1989) Specification for copper refinery
BS 5724 Medical electrical equipment.
shapes.
Part 1 General requirements for safety.
Part 2 Particular requirements for safety.
BS 1319: 1976(1986) Specification for medical gas
Section 2.12: 1990 Specification for lung
cylinders, valves and yoke connections.
ventilators.
Section 2.13: 1990 Specification for anaesthetic
BS 1710: 1984(1991) Specification for identification
machines.
of pipelines and services.

BS 6387: 1994 Specification for performance
BS 1780: 1985(1992) Specification for bourdon tube
requirements for cables required to maintain circuit
pressure and vacuum gauges.
integrity under fire conditions.

211

References

BS 6834: 1987 (1992) Specification for active standards for anaesthetic agents. Department of
anaesthetic gas scavenging systems. Health, 1996.

BS 6759 Safety valves. Anaesthetic agents: controlling exposure under
Part 2: 1984 Specification for safety valves for COSHH. Health Service Advisory Committee.
compressed air or inert gases.
Code of practice 19 Bulk liquid oxygen storage at
BS 7226: 1989 Methods of test for performance of users premises (Revision 2). British Compressed Gases
inlet air cleaning equipment for internal combustion Association, 1996.
engines and compressors.
Medical gas pipe systems. Design and installation of
EN 1251 Cryogenic vessels – transportable vacuum (QAS 3720.1/206). BSI/Department of Health, 1988.
insulated of not more than 1000 litres volume –
operational requirements. Guidance notes for users of liquid cylinders of low
pressure cryogenic liquid supply vessels for liquid
oxygen, nitrogen or argon with capacity of under
450 litres (G4521). BOC Gas, 1996.
NHS Estates publications

Model Engineering Specifications. NHS Estates. 1993
(amended 1995)

Firecode

Health Technical Memoranda (HTMs)

81 Fire precautions in new hospitals. NHS Estates.
The Stationery Office, 1996.

82 Alarm and detection systems. NHS Estates. The
Stationery Office, 1996.

Health Technical Memoranda (HTMs)

2007 Electrical services supply and distribution. NHS
Estates. The Stationery Office, 1993. (issued in 4 parts).

2011 Emergency electrical services. NHS Estates. The
Stationery Office, 1993. (issued in 4 parts).

2014 Abatement of electrical interference. NHS
Estates. The Stationery Office, 1993. (issued in 4 parts).

2015 Bedhead services. NHS Estates. The Stationery
Office, 1994-95. (issued in 3 parts).

2025 Ventilation in healthcare premises. NHS Estates.
The Stationery Office, 1994. (issued in 4 parts).

Miscellaneous publications

Occupations exposure standards for anaesthetic
agents (EL(96)33). Department of Health, 1996.

Advice on the implementation of the Health and
Safety Commissions occupational exposure

212

Other publications in this series

(Given below are details of all Health Technical Component Data Base (HTMs 54 to 80)
Memoranda available from The Stationery Office. HTMs 54.1 User manual, 1993.
marked (*) are currently being revised, those marked (†) 55 Windows, 1989.*
are out of print. Some HTMs in preparation at the time of 56 Partitions, 1989.*
publication of this HTM are also listed.) 57 Internal glazing, 1995.
58 Internal doorsets, 1989.*
1 Anti-static precautions: rubber, plastics and fabrics† 59 Ironmongery.*
2 Anti-static precautions: flooring in anaesthetising 60 Ceilings, 1989.
areas (and data processing rooms), 1977. 61 Flooring, 1995.
3–4 – 62 Demountable storage systems, 1989.
2005 Building management systems, 1996. 63 Fitted storage systems, 1989.
2007 Electrical services: supply and distribution, 1993. 64 Sanitary assemblies, 1995.
2009 Pneumatic air tube transport systems, 1995. 65 Health signs*
2010 Sterilization, 1994, 1995, 1997. 66 Cubicle curtain track, 1989.
2011 Emergency electrical services, 1993. 67 Laboratory fitting-out system, 1993.
2014 Abatement of electrical interference, 1993. 68 Ducts and panel assemblies, 1993.
2015 Bedhead services, 1994, 1995. 69 Protection, 1993.
2017 Health building engineering installations: 70 Fixings, 1993.
commissioning and associated activities.* 71 Materials management modular system, 1993.*
2020 Electrical safety code for low voltage systems, 1993. 72 to 80 –
2021 Electrical safety code for high voltage systems, 1993,
1994.
Firecode
2023 Access and accommodation for engineering
services, 1995.
81 Firecode: fire precautions in new hospitals, 1996.
2024 Lifts, 1995.
82 Firecode: alarm and detection systems, 1996.
2025 Ventilation in healthcare premises, 1994.
83 Fire safety in healthcare premises: general fire
2027 Hot and cold water supply, storage and mains
precautions, 1994.
services, 1995.
84 Firecode: fire safety in residential care premises
2030 Washer-disinfectors, 1995.
(applicable in Northern Ireland only), 1995.
2031 Clean steam for sterilization, 1997.
85 Firecode: fire precautions in existing hospitals, 1994.
2035 Mains signalling, 1996.
86 Firecode: fire risk assessment in hospitals, 1994.
2040 The control of legionellae in healthcare premises –
87 Firecode: textiles and furniture, 1993.
a code of practice, 1994.
88 Fire safety in healthcare premises: guide to fire
2045 Acoustics, 1996.
precautions in NHS housing in the community for
2050 Risk management in the NHS estate, 1994.
mentally handicapped/ill people, 1986.
2055 Telecommunications (telephone exchanges), 1994.
2060 Supply and treatment of water.*
Health Technical Memoranda published by The Stationery
2065 Waste guidance.*
Office can be purchased from SO bookshops in London
2070 Estates emergency and contingency planning, 1997.
(post orders to PO Box 276, SW8 5DT), Edinburgh, Belfast,
2075 Clinical waste disposal: alternative technologies.*
Cardiff, Manchester, Birmingham and Bristol, or through
good booksellers. SO provide a copy service for
publications which are out of print; and a standing order
service.

Enquiries about Health Technical Memoranda should be
addressed to: NHS Estates, Department of Health,
Publications Unit, 1 Trevelyan Square, Boar Lane, Leeds
LS1 6AE.

213

About NHS Estates

NHS Estates is an Executive Agency of the Department of Health Technical Memoranda – guidance on the design,
Health and is involved with all aspects of health estate installation and running of specialised building service
management, development and maintenance. The Agency systems, and on specialised building components. SO
has a dynamic fund of knowledge which it has acquired
during over 30 years of working in the field. Using this Health Facilities Notes – debate current and topical
knowledge NHS Estates has developed products which are issues of concern across all areas of healthcare provision.
unique in range and depth. These are described below. SO
NHS Estates also makes its experience available to the field
through its consultancy services. Encode – shows how to plan and implement a policy of
energy efficiency in a building. SO
Enquiries about NHS Estates should be addressed to:
NHS Estates, Publications Unit, Department of Health, Firecode – for policy, technical guidance and specialist
1 Trevelyan Square, Boar Lane, Leeds LS1 6AE. aspects of fire precautions. SO
Telephone 0113 254 7000.
http://www.demon.co.uk/nhsestates/hpage.html/ Capital Investment Manual Database – software
support for managing the capital programme. Compatible
with Capital Investment Manual. NHS Estates

Some NHS Estates products Model Engineering Specifications – comprehensive
advice used in briefing consultants, contractors and
Activity DataBase – a computerised briefing and design
suppliers of healthcare engineering services to meet
system for use in health buildings, applicable to both new
Departmental policy and best practice guidance.
build and refurbishment schemes. NHS Estates
NHS Estates

Design Guides – complementary to Health Building
Quarterly Briefing – gives a regular overview on the
Notes, Design Guides provide advice for planners and
construction industry and an outlook on how this may
designers about subjects not appropriate to the Health
affect building projects in the health sector, in particular
Building Notes series. SO
the impact on business prices. Also provides information
on new and revised cost allowances for health buildings.
Estatecode – user manual for managing a health estate.
Published four times a year; available on subscription
Includes a recommended methodology for property
direct from NHS Estates. NHS Estates
appraisal and provides a basis for integration of the estate
into corporate business planning. SO
Items noted “SO” can be purchased from The Stationery
Office Bookshops in London (post orders to PO Box 276,
Concode – outlines proven methods of selecting contracts
SW8 5DT), Edinburgh, Belfast, Manchester, Birmingham
and commissioning consultants. Reflects official policy on
and Bristol or through good booksellers.
contract procedures. SO

Works Information Management System –
a computerised information system for estate NHS Estates consultancy service
management tasks, enabling tangible assets to be put into
the context of servicing requirements. NHS Estates Designed to meet a range of needs from advice on the
oversight of estates management functions to a much
Health Building Notes – advice for project teams fuller collaboration for particularly innovative or exemplary
procuring new buildings and adapting or extending projects.
existing buildings. SO
Enquiries should be addressed to: NHS Estates Consultancy
Health Guidance Notes – an occasional series of Service (address as above).
publications which respond to changes in Department of
Health policy or reflect changing NHS operational
management. Each deals with a specific topic and is
complementary to a related HTM. SO

214

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