Effects of ambient pressure on smoke movement and temperature distribution in inclined tunnel fires

A series of simulations with regard to inclined road tunnel were conducted to investigate the effect of ambient pressure on smoke movement and temperature distribution. The tunnel slope and ambient pressure were systematically changed. When a fire breaks out in an inclined tunnel, the thermal buoyancy induced by smoke temperature difference will induce an airflow through the tunnel due to the stack effect. The induced longitudinal airflow is a key factor in inclined tunnel fires. Under the combined effect of induced longitudinal airflow and ambient pressure, the smoke movement and temperature distribution pattern are presented firstly. Then the variation of induced longitudinal airflow velocity with tunnel slope and ambient pressure is explained. Finally, taking the tunnel slope, the ambient pressure and the velocity of resulted induced longitudinal airflow into account, a correlation predicting the maximum smoke excess temperature beneath the ceiling is proposed. Moreover, the correlation agrees well with previous experimental results at normal pressure. The results can provide an engineering reference for tunnel structural fire protection, smoke control and safe evacuation in inclined tunnels at different ambient pressures.