A study of fire smoke spreading and control in emergency rescue stations of extra-long railway tunnels

An emergency rescue station providing a link across the two neighboring tubes in an extra-long railway tunnel is an integral part of evacuation routes in the event of a train fire. Inhalation of toxic gases and hazardous smoke is a major cause of fire deaths. Therefore it is of key importance to reserve escape routes, in upstream of the fire source and cross passages, clear of the poisonous substances by supplying fresh air to the cross passages and the tunnel in which the train on fire draws up simultaneously. In this study, numerical simulations were carried out with the Fire Dynamics Simulator, given parameters of a real tunnel, to determine the optimal air flow. The influence of air flow on the spread of gases and smoke and the distribution of temperature was also investigated. Analysis of the results show that a sufficient air flow along the tubes may effectively limit the thickness of the smoke layer, thus leaving adequate risk-free space above the ground for the emergency evacuation. An air flow in excess of the optimum, however, results in significant non-uniformly distributions of the smoke layer over the evacuation paths, which causes an increase in risk. Further, pressurized air supply in the cross passages proves beneficial to the reduction in the air temperature and in the dimensions of certain regions, whereas it exerts an insignificant effect on the thermal radiation of the fire source. Accordingly fire suppression systems, e.g., curtain producing sprinklers, are expected in emergency rescue stations.