Numerical simulation Simultaneous use of longitudinal ventilation and smoke extraction from the ceiling in fires inside tunnels

Ventilation is essential to provide a smoke-free path for safe passenger evacuation and effective rescue services in case of a tunnel fire, because the closure tunnels increase consequences of accidents significantly. In the present study, the simultaneous use of longitudinal ventilation and smoke extraction from the ceiling in fires inside tunnels and physical phenomena has been investigated. Fire dynamics simulator will be used as a CFD tool. This simulation was performed to investigate the effect of the longitudinal distance of the smoke extraction system from the fire source on the smoke back-layering length and the maximum temperature in the two operating conditions used by this system downstream and upstream the fire source. In the present work, the smoke extraction system is located on the ceiling of the tunnel. The results show that using a smoke extraction system upstream the fire source will increase the maximum temperature, but using the same system downstream will reduce the temperature throughout the tunnel and prevent smoke back-layering. However, attention to the smoke extraction velocity for prevent the plug-holding phenomenon. The results also show that the simultaneous use of two smoke extraction systems at the upstream or downstream of the fire source will have a better result and The maximum temperature is reduced by 10%.