Numerical Simulation Study Of Road Tunnel Fire Danger Under Traffic Congestion Condition

Tunnels can overcome terrain obstacles such as mountains, lakes, rivers, shorten the route mileage and travel time, and has been widely used in highway network construction; their number and length are growing. Considering the narrow and closed space in the tunnel, in case of fire, under the action of longitudinal wind, the toxic smoke with high temperature released by the fire source will quickly spread along the tunnel. The smokes threaten the occupants, vehicles, equipments and structures in the tunnel, the consequences are more severe than fires in an open space. While the road traffic volume is rising, many design and constructions of tunnel did not fully consider the future development of traffic, the tunnel traffic congestion phenomenon is becoming increasingly common. Congestion can cause vehicle distance decreasing, and has impact on the frequency, scale, progress and occupants evacuation in tunnel. Therefore, it is necessary to research the tunnel fire under traffic congestion conditions.Based on the characteristics of tunnel fire and driving behavior under traffic jam, the relationship of traffic congestion, tunnel fire and occupants evacuation has been in-depth analysis. Taking Bapanshan tunnel in which traffic jam often occurred as study object; model of tunnel fire under traffic congestion condition has been established with the Fire Dynamic Simulator (FDS) software. The ignition condition of vehicle has been discussed based on heat flux guidelines as criteria. Through the tunnel fire characteristic parameters obtained in numerical simulation, the time evolution of smoke and ceiling temperature in different ignition conditions has been studied.The results show that vehicles downstream of the tunnel have a disturbance effect on smoke movement. On the effect of ignition, the temperature, thermal radiant, visibility distance downstream the tunnel overrun phenomenon appear7-10min after fire begin, the degree of out of gauge is directly related to the type of vehicle being ignited. When it comes to HGV ignited, the fire will start to propagation along the tunnel in two directions both upstream and downstream the fire source. Meanwhile, traffic congestion has impact on occupants walking speed when evacuation. With longitude air velocity of2.5m/s, after the vehicle ignited, the pedestrian crosswalk space settings of400m cannot guarantee the safety evacuation of people far away from the exit. Finally, risk control measures of tunnel fire under traffic congestion conditions has been proposed from the traffic capacity of tunnel export improvement, traffic guidance and fire emergency three aspects. The results can provide reference for future tunnel design and operation.