The rapid urbanization in China has led to many utility tunnels containing a variety of municipal pipelines including natural gas, heating, water and electrical power that are key infrastructure components in cities. The most dangerous hazard is the natural gas pipelines that can leak to form explosive gas clouds in the confined tunnels which brings huge explosion risks to the safe operation of the utility tunnels. The propagation characteristics of gas explosions in a complex, confined utility tunnel were studied experimentally as a function of various factors to support safety control and assessments of gas explosions in utility tunnels. The experiments studied the effects of methane concentration, pressure relief ports and auxiliary facilities such as the gas pipeline design, distribution boxes and fire boxes on the flame propagation and the overpressures. The results show that the maximum overpressure occurs for a methane concentration of 9.5%, vents in the tunnel significantly reduce the overpressures compared with closed utility tunnels, and the peak overpressure attenuation rate is 28.4%. Auxiliary facilities in the tunnel accelerate the flame propagation and lead to greater overpressures. This study provides guidance for improving disaster mitigation for natural gas utility tunnels in cities.
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