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

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.