The Effect of Longitudinal Ventilation System on Smoke Movement and People's Evacuation in Tunnel Fire

Smoke movement in a model tunnel controlled by longitudinal ventilation system was studied and in this paper. Smoke movement in a tunnel was studied numerically with some equations reviewed. A numerical experiment with Computational Fluid Dynamics (CFD) was carried out. At the initial stage of tunnel fire, the velocity of ventilation fans can be set up as critical speed to slow down smoke movement and high temperature diffusion. However, in evacuation stage, the ventilation speed should be decreased to prevent smoke transmit too fast and hurt people in the downstream. Without longitudinal ventilation system, smoke is distributed symmetrically in the tunnel. When the tunnel has longitudinal ventilation system, smoke will not distribute in the upstream of the tunnel but it will spread quickly to the downstream. If people still evacuate along the center line of the downstream, they may be threatened by the smoke. This study demonstrated both the advantages and disadvantages of longitudinal ventilation system and showed that the velocity of ventilation fans should be carefully chosen.