A study of optimal arrange of vent in a subway station

The subway station is a special location with very dense crowd. Because subway station situates in underground, people can not evacuate to ground easily. Once a fire occurs in subway station, it is very dangerous for people to stay in it. So, a well designed smoke exhaust system must be installed in subway station to control the smoke's propagation and descending. Usually, the ceiling screens are placed above the platform's ceiling, and produce several smoke reservoirs in the top of platform layer. Because smoke extraction in a subway station is depended on the duct laid above the ceiling, so the position of vents is situated in the same level of platform layer's ceiling. As a result, the height of vents is lower than the smoke reservoir. If subway station catches a fire, smoke will cumulate in smoke reservoirs at the beginning, mechanical fan can not exhaust any smoke in this process. When smoke layer descend below vents' height, mechanical fan can work authentically, due to the thin smoke layer underneath the ceiling, a mass of air is exhausted by mechanical fan instead of fire smoke. This situation will weaken the effect of smoke exhaust greatly. This paper uses a CFD technique FDS4.0 to simulate smoke's movement in a side platform of an actual subway station during a fire, schemes out several smoke exhaust plan, compares the result of simulation under different height of vents, different depth of smoke reservoirs and the same volume flux of mechanical fan.