Zone Simulation Of Fire Smoke Spreading And Controlling In Subway Platform

Study of the smoke movements in city subway has a significant meaning for our society and environment, when we design subway platform and assess, rescue or defend subway fire. By mathematical simulation, analyses of subway fire smoke movements and controls are carried out. First, a summary of present status is given for the movements and controlling of subway fire at home and on abroad. By use of basic idea of zone model, each room can be classified into two zones: upper layer where smoke is relatively hot and lower layer where air is relatively cool, meanwhile assuming that all physical parameters within each zone are uniform, a set of governing differential equations are derived by the conservation principles of mass, energy as well as the ideal gas law. Each dividing process is described by a source term of the equations. These dividing process are combustion chemistry, plume, ceiling jet, vertical &horizontal vent flows, convective, conductive and radiant heat transfer. A stiffly stable multi-step method for ODE'S on the basis of C.W.Gear's work is applied to solve the set of equations. For a two-layer subway platform, analyses on fire critically dangerous condition are carried out. On the base of it, people evacuation times nearby fire source, in platform and in hall are calculated individually, which are used as a criterion to judge different measures of preventing and ejecting smoke. In order to achieve better calculation precision, the station is divided into 24/28 calculation rooms. CFAST software is applied to individually calculate changing laws about smoke temperature, height, CO density changed by the time. The numerical simulations are carried out under many different conditions when having or not having blocks, sprinklers, sending air etc and fire's location are platform's central part and end part. The influence of ejecting smoke mechanically, orifices of ejecting smoke, sending air mechanically, sprinkler devices, walls of preventing smoke on smoke movements are studied. The simulation results give the best ways about controlling subway fire smoke spreading and benefiting people's evacuation are provided. The results are: whether fire occurs at platform's central part or end part, only sprinkler, blocks, sending air to stairs, ejecting smoke working together can produce a best airflow in subway station, which mostly benefits people evacuation.