The Evaluation of Methane Gas Explosion Risk in Confined Spaces - A Case Study in the Ship Building Industry

Abstract

Hydrocarbon gas explosions such as Methane gas in confined spaces represent a significant hazard across various industries, particularly mining, oil and gas extraction, and oxy-cutting processes. The risks associated with methane accumulation are exacerbated by the unique characteristics of confined environments, where gas concentrations can reach explosive levels. The explosive potential of methane is primarily influenced by its concentration in the air. Methane can form explosive mixtures when present in the air at concentrations ranging from approximately 5% to 15% by volume, known as the lower explosive limit (LEL) and upper explosive limit (UEL), respectively (Jia, 2023). Understanding the conditions under which methane becomes hazardous is crucial for developing effective safety protocols and mitigation strategies. This study is based on a truth gas leak near-miss incident. According to the study results, When approximately 2 kg of methane gas leaks (within 2 hours for 12 % leak cross-section) into a 169 m3 confined space, the ambient atmosphere reaches the lower explosion limit (LEL %5 v/v). The stoichiometric volume fraction in the air is 9.5 % (v/v) for methane (CH4) gas. This stoichiometric ratio equals approximately 10 kg of methane gas for a confined space volume of 169 m3. The methane gas escaping from the leak cross-sectional area of approximately 80% and 10% of the hose diameter may create an explosive atmosphere (10 kg methane gas LEL 9.5 %v/v) in a confined space of 169 m3 in approximately 15 minutes and 15 hours, respectively. According to the consequence analysis evaluation; the explosion of this amount of methane gas may be fatal. After an explosion caused by 10 kg of methane gas in the Ballast tank, a worker standing 1 m away will be exposed to 1523 kPa of overpressure. When an evaluation is made with a 1 s positive phase duration, the mortality rate due to lung damage, one of the most important air-entering body organs, is standing 1 m away will be exposed to 1523 kPa of overpressure. When an evaluation is made with a 1 s positive phase duration, the mortality rate due to lung damage, one of the most important air-entering body organs, is estimated as 93%. This situation may have more dramatic consequences depending on the number of people in the ballast tank.

Keywords

• Gas Explosion
• Explosion risk in Confined Spaces
• Consequence Analysis

The Evaluation of Methane Gas Explosion Risk in Confined Spaces – A Case Study in the Ship Building Industry

Abstract

Hydrocarbon gas explosions such as methane gas in confined spaces represent a significant hazard across various industries, particularly mining, oil and gas extraction, and oxy-cutting processes. The risks associated with methane accumulation are exacerbated by the unique characteristics of confined spaces, where gas concentrations can reach explosive levels. The explosive potential of methane is primarily influenced by its concentration in the air. Understanding the conditions under which methane becomes hazardous is crucial for developing effective safety protocols and mitigation strategies. This study is based on a truth gas leak near-miss incident in the shipyard ship building department. Before this study, there were many records of gas leaks due to hose and torch connection points and hose damage in oxy-fuel cutting operations. During the confined spaces (ballast, cargo, service, settling tanks etc.) gas free measurements on April 8, 2024, we detected a methane gas leak reaching explosive concentrations originating from a damaged welding hose. In this study, the question of what would happen if this explosive atmosphere in the confined space exploded under optimum conditions was answered. According to the results of the study, the explosive methane gas concentration in a 169 m3 confined space (ballast tank) was approximately 10 kg methane gas mass, and the methane gas leak of 80 % of the hose cross-section diameter reached an explosive concentration within 15 minutes. The amount of 10 kg methane gas leaking into the 169 m3 confined space was equivalent to the 95000 ppm (9.5 % v/v) methane gas concentration required to provide optimum explosion conditions. After an explosion caused by 10 kg of methane gas in the ballast tank (169 m3), a worker standing 1 m away will be exposed to 1523 kPa of overpressure. 10 kg methane gas used for the explosion scenario represents the stoichiometric fuel/air mixture (95000 ppm). When the evaluation is made by taking into account the 1 s positive phase duration, the mortality rate due to lung damage, which is one of the organs most exposed to air, means that a person standing 1 m away is exposed to 1523 kPa overpressure and the probability of death (Pr) is estimated as 93%. This result may have more dramatic consequence depending on the number of people in the ballast tank.

Keywords

• Gas explosion
• Explosion risk in confined spaces
• Consequence Analysis

References

1. Izci, F. B., Gökyay, O., & Barlas, B. (2024). Investigation of non-fatal occupational accidents and their causes in Turkish shipyards. International journal of occupational safety and ergonomics, 30(1), 33-40.
2. Kravtsov, A. N., Zdebski, J., Svoboda, P., & Pospichal, V. (2015, May). Numerical analysis of explosion to deflagration process due to methane gas explosion in underground structures. In International Conference on Military Technologies (ICMT) 2015 (pp. 1-9). IEEE.
3. Chen, H. (2015). Gas explosion technology and biomass refinery (No. 11551). Springer Netherlands.
4. Garrison, R. P., & McFEE, D. R. (1986). Confined Spaces–A Case for Ventilation. American Industrial Hygiene Association Journal, 47(11), A-708.
5. Green, D. W. (2008). Perry’s chemical engineers’. Handbook–seventh Edition–Sections, 5-12.
6. De Santoli, L., Paiolo, R., & Basso, G. L. (2017). An overview on safety issues related to hydrogen and methane blend applications in domestic and industrial use. Energy Procedia, 126, 297-304.
7. Han, Z. Y., & Weng, W. G. (2011). Comparison study on qualitative and quantitative risk assessment methods for urban natural gas pipeline network. Journal of hazardous materials, 189(1-2), 509-518.
8. Mercedes G.M., Munoz M., Casal J., Radiant heat from propane jet fires, Experimental Thermal and Fluid Science, 34, 323-339, 2010.

9. Miranda, J. T., Camacho, E. M., Formoso, J. F., & García, J. D. D. R. (2013). Comparative study of the methodologies based on Standard UNE 60079/10/1 and computational fluid dynamics (CFD) to determine zonal reach of gas-generated Atex explosive atmospheres. Journal of Loss Prevention in the Process Industries, 26(4), 839-850.
10. Kwon, S., & Park, J. C. (2015). A review of TNT equivalent method for evaluating explosion energy due to gas explosion. Explosives and Blasting, 33(3), 1-13.
11. Assael, M. J., & Kakosimos, K. E. (2010). Fires, explosions, and toxic gas dispersions: effects calculation and risk analysis. CRC Press.
12. Finlay, S. E., Earby, M., Baker, D. J., & Murray, V. S. (2012). Explosions and human health: the long-term effects of blast injury. Prehospital and disaster medicine, 27(4), 385-391.
13. Lees, F. (2012). Lees' Loss prevention in the process industries: Hazard identification, assessment and control. Butterworth-Heinemann.
14. Wightman, J. M., & Gladish, S. L. (2001). Explosions and blast injuries. Annals of emergency medicine, 37(6), 664-678.
15. Crowl, D. A., & Louvar, J. F. (2001). Chemical process safety: fundamentals with applications. Pearson Education.
16. Yue, C., Chen, L., Li, Z., Mao, Y., & Yao, X. (2023). Experimental study on gas explosions of methane-air mixtures in a full-scale residence building. Fuel, 353, 129166.