Explosion mechanism analysis during tunnel construction in the Zengwen Reservoir

The objective of this paper is to investigate the accident cause and uses CFD model to simulate the impact of an explosion occurred in Zengwen Reservoir. An explosion occurred during a tunnel construction at Zengwen Reservoir, which caused a cement mixer parked at the tunnel entrance to fly 10 m out, while also killing two workers inside the tunnel. In the past, it was difficult to carry out quantitative analysis for such explosions. This research conducted field investigation on the scene after the explosion to investigate the cause, while collecting gas samples within and near the tunnel entrance for GC–MS analysis. By comparing samples from different sections of the diversion tunnel, a methane concentration of 94.86% was discovered near the area of ignition. The tunnel model was built using FLACS v10.4 to simulate the explosion scenarios. Under 1.1 kg/s leakage rate (5.47% methane concentration), overpressure caused by the explosion could not reach the tunnel entrance. An increase to 1.3 kg/s leakage rate would yield an explosion overpressure of 0.44 bar, which is close to the force needed to overturn a vehicle. Other higher concentrations of methane caused overpressures exceeding that value, but were less indicative of the scenario at that time. This research showed the use of GC–MS during investigation was crucial in identification of substance composition. In addition, this case study showed FLACS software could predict and perform numerical quantification of the gas leakage and diffusion conditions, while it could also aid in the evaluation of gas explosion scenarios in accident investigations.