Critical roof opening longitudinal length for complete smoke exhaustion in subway tunnel fires

A series of experiments were conducted to investigate the smoke exhaustion in a subway tunnel under natural ventilation with a wide roof opening (its width is equal to tunnel width) based on a 1/10 reduced-scale tunnel model. The effect of the roof opening longitudinal length on the smoke exhaustion was addressed both theoretically and experimentally. The results indicated that there existed a critical opening longitudinal length which allows a complete smoke exhaustion under fire conditions. The critical opening longitudinal length was related to the tunnel aspect ratio and the distance between fire source and roof opening. A theoretical model was also developed to predict the critical opening longitudinal length for subway tunnel. The research outcomes of this study provide a technical guide for the future subway tunnel design.