Investigation of effective parameters on critical ventilation velocity in underground tunnels

Due to the importance of safety in underground tunnels and the health of passengers in emergency modes, analysis and simulation of fires in tunnels and design an appropriate and efficient ventilation system to reduce damages from fire hazards is necessary. Longitudinal ventilation system is widely used in tunnel ventilation. The critical ventilation velocity in longitudinal system is the amount of airflow necessary to prevent backlayering of smoke and heat to upstream of fire region. The lower air velocity leads to influence of smoke and heat of fire to the fire upstream, and resulting in reduction of visibility and fresh air in the tunnel. In critical velocity, smoke and heat moves to the downstream of the tunnel providing fresh air and a safe passage for passengers to escape. The aim of this research is to investigate the critical ventilation velocity and effective parameters on it. CFD simulation were performed in this paper to study the critical ventilation velocity by using the code FDS. The effect of fire source shape, vehicle such as a train inside the tunnel, tunnel geometry and slope on the critical ventilation velocity were investigated