Experimental Study on Toxic Gas Produced during Pipeline Gas Explosions

International Journal of Scientific and Technical Research in Engineering (IJSTRE)
www.ijstre.com Volume 3 Issue 1 ǁ January 2018.
Manuscript id. 214563900 www.ijstre.com Page 14
Experimental Study on Toxic Gas Produced during Pipeline Gas
Explosions
JIA Zhi-wei1,2
XU Sheng-ming1
（1.School of Safety Science and Engineering, Henan Polytechnic University, Jiaozuo, 454003, China
2.Central Plains Economic Zone Coal Methane cooperative innovation center in Henan Province，Jiaozuo, 454003, China）
Abstract: Dangerous gas explosion accidents result in considerable amount of casualties and property damage.
Hence, an investigation on the generation of poisonous gases in gas explosions exerts important implications
for accident prevention and control and in the decision-making processes of fire rescue. Therefore, a gas
explosion piping test system is established in this paper. Experimental research on gas explosion is conducted by
selecting methane/air premixed gases with concentrations of 7%, 9%, 11%, 13%, and 15% in the gas explosive
range. This research aims to reveal the regularity of CO generation after gas explosion in pipelines.
Experimental results showed that when the gas concentration is small (< 9%), 1500–3000 ppm CO will be
produced. When the gas concentration is large (> 9%), the CO amount will reach 3000–40000 ppm. The
variation trend in CO concentration and the quantity of explosive gas are also obtained.
Key Words: gas explosion, piping test system, gas concentration, CO concentration
I. Background and significance of the study
Approximately 95% of China’s coal is obtained through underground mining, which involves complex
geological conditions and relatively adverse working environments. In 2013, the average mining depth of large
and medium coal mines is 650 m; the mining depth of Pingdingshan coal mine in Henan Province is 1000 m,
which extends downward with an average annual rate of 10 m [1-3]
. With the increased coal mining depth, the gas
content and pressure in the coal and the gas emission quantity also increase, thereby causing increasingly severe
gas explosions and coal and gas outbursts. In recent years, with the gradual increase in the coal mine safety
management level and safety investment in China, the death rate per million ton coal decreases annually, and
gas disaster has been effectively controlled [4-5]
. Nevertheless, in 2013, the death rate per million tons of coal in
China remains 10 times that of the United States; additionally, the death rate from gas and coal dust explosions
still exceeds 100 each year [6-7]
. In the past 10 years, considerable local and international research has been
performed about the factors influencing the gas explosion generation and the effects of shape, size, angle, and
wall roughness of underground roadway on the generation of flame and wave during gas explosion [8-14]
.
However, study on the mechanism and propagation law of gas explosion is still limited. In particular, research
on the generation and influencing factors of toxic gas during gas explosion lacks a system. Results cannot also
provide guidance on disaster relief decision for gas explosion accidents. Major coal dust explosion accidents
result in a substantial amount of casualties and property losses, a remarkable psychological trauma to the people,
and negative effects on the community. Therefore, research on the generation of shock wave, flame, and toxic
gas during gas explosion presents important guiding significance for accident control and disaster relief decision
[15]
. The generation and propagation of toxic gas, which causes considerable harm, should be investigated. The

Experimental Study on Toxic Gas Produced during Pipeline Gas Explosions
obtained research results are largely important for estimating the diffusion range of toxic gas in underground
tunnel after gas explosion accidents.
II. Experimental study on carbon monoxide produced by gas explosion in pipelines
2.1 Establishment of experimental systems
In this experiment, we used the experimental system with a total length of 20.9 m. The explosion pipeline
showed a dimension of 80 mm × 80 mm. The gas explosion concentrations of 7%, 9%, 11%, 13%, and 15% of
methane/air premixed gas were selected to produce CO. We concluded that the CO amount in the gas explosion
accident is associated with the change in gas concentration. The schematic diagram of the gas explosion
experiment system is shown in Fig. 1.
1 2 3 4
5 6 7 8 9 10 11 12
1 - High Energy Ignition Device, 2 - Vacuum Flow Meter, 3 - Spherical Valve, 4 – Poison Gas Collection, 5–8
Front CO Detection Point, 9–12 Rear CO Detection Point
Figure 1 Gas explosion experiment system
Prior to the experiment, the spherical valve was opened. The vacuum pump was picked up at point 4, the
pipe was evacuated, the spherical valve was closed, and the gas with different concentrations was injected by the
vacuum flow meter. The gas explosion started at the ignition device and continued in the ball valve on the left
side of the pipeline. Points 5–8 were used to measure the gas explosion generated by the CO concentration. The
distance between points 5–8 and point 1 was 0.25, 1.35, 2.2, and 3.95 m, respectively. The physical model of the
experimental gas explosion system is shown in Figs. 2 and 3.
Figure 2 Cavity gas explosion experiment Figure 3 Gas explosion experimental
pipe system
2.2 Experimental data and treatment
Gas explosion with different gas concentrations (30 times) produced six groups of CO. Experimental results
are shown in Table 1。

Table 1 Relationship between each measuring point and the gas concentration
CH4 concentration
／%
CO concentration／ppm
Measuring point1 Measuring point2 Measuring point3 Measuring point4
7 1550 1600 1550 1400
9 2100 1900 1550 2200
11 16300 15200 17500 10700
13 26750 31050 28350 29500
15 39300 36900 32500 40300
7 1350 1400 1200 1750
9 2200 1350 1400 1700
11 11250 12000 11000 14550
13 27750 28050 29350 30500
15 33300 37000 31500 40500
7 1650 1750 1300 1400
9 2400 2200 2000 2150
11 13250 12050 13050 14550
13 28500 29150 29550 28700
15 39500 43200 44050 39500
7 1850 1300 1650 1400
9 2150 2150 2150 2150
11 11250 14050 11050 10050
13 31750 28350 29650 27850
15 39050 30500 32050 36500
7 1550 1350 2450 1050
9 2100 2050 1800 1350
11 13050 10500 11050 10300
13 31750 29000 30750 31550
15 35050 38050 40450 36750
7 1700 1350 1300 1650
9 2200 1700 1450 2050
11 13300 12500 13200 14300
13 28550 29350 31050 29850
15 33050 39500 27050 37050
The six groups of experimental results were averaged. The relationship between the gas concentration and
CO concentration was determined through the gas explosions with different concentrations, as shown in Fig. 4.

Figure 4 CO concentration with prefilled gas concentration
The relationship between CO and the amount of explosion gas involved in the enclosed confined space was
obtained using the following equations:
2 . 3 2 4 8
8 6 9 . 8 8xy  ;
9359.02
R .
III. Data analysis and conclusion
The amount of CO produced after a gas explosion in the pipeline is related to the concentration of the gas
during explosion. Therefore, the gas concentration determines the peak density of CO. When the gas
concentration exceeds 9%, the CO concentration also increases evidently; high gas concentration results in a
large amount of CO produced. This result is attributed to that when the gas concentration is small (< 9%), the
amount of oxygen in contact with the gas is relatively abundant. Consequently, methane can be fully reacted.
Given that the gas density is less than that of air, a stratified phenomenon occurs in the pipeline mixing process:
the gas is in the upper part, and the air is in the lower part. A small amount of gas combustion during explosion
is insufficient, thereby producing a small amount of CO. When the gas concentration is relatively large (> 9%),
the reaction occurs when the critical point begins to react strongly with a highly representative reaction.
Furthermore, the oxygen cannot fully support all methane combustion, and the amount produced by the CO
increases rapidly with increased gas concentration.
Experimental data analysis resulted in the following conclusions:
(1) When the gas concentration is small (< 9%), the gas explosion will produce a small amount of CO
(1500–3000 ppm). By contrast, when the gas concentration is relatively large (> 9%), the gas explosion will
produce a large amount of CO (3000–40000 ppm).
(2) High gas concentration results in large amount of CO produced. The following relation is also
obtained: 2.3248
869.88xy  .
IV. Acknowledgement
This study was supported by Program for National Natural Science Foundation of China (No.51774120).

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