A study for predicting the maximum gas temperature beneath ceiling in sealing tactics against tunnel fire

Sealing the tunnel portal is one of practical strategies for tunnel fire extinguishing. In order to better comprehend the sealing effects on tunnel fire and help with sealing strategies scientifically, the maximum gas temperature beneath ceiling in a sealing fire was investigated theoretically, experimentally and numerically in this paper. The results show that maximum ceiling gas temperature is greatly affected by sealing ratio, which probably due to the comprehensive effect between fresh air supply and the reduction of heat loss significantly related to vent area of tunnel portal. Moreover, there always exists a critical sealing ratio, at which ceiling temperature would reach the maximum, and when beyond the critical sealing ratio, maximum gas temperature would drop gradually, which is expected in firefighting. Also, it is found that critical sealing ratio is a function of dimensionless heat release rate, and the greater the heat release rate is, the smaller the critical sealing ratio would be. Finally, an empirical model determining maximum ceiling gas temperature is developed to modify the current models by taking sealing effect into account. The predictions calculated by modified equations agree well with experimental and numerical date in maximum ceiling gas temperature.