| In recent years,with the increase of the length and quantity of highway tunnels in China,as well as the increase of driving speed and traffic flow,the fire accidents caused by fault,collision and spontaneous combustion of goods occur frequently when vehicles are driving in tunnels.According to a large number of accident statistics,the large number of toxic and harmful smoke produced by tunnel fire is the main cause of heavy casualties,while the smoke of long distance tunnel is more harmful to people because of the relatively closed internal space and the single rescue and escape route.Therefore,it is of great significance to study the smoke spreading law of long distance tunnel fire to ensure the safety of evacuation and rescue workers.Based on the theoretical analysis of fire smoke spreading in static open environment and narrow confined space of tunnel,this paper concludes that the development process of fire plume in tunnel can be divided into vertical ascending stage,impact ceiling stage,radial diffusion stage,transition stage and one-dimensional vertical spreading stage.Based on the analysis of smoke temperature,flow velocity and smoke concentration,the models of smoke diffusion temperature field,velocity field and smoke concentration field in tunnel fire are established.The critical value of determining fire smoke risk factors(temperature,radiant heat,CO concentration,visibility)is obtained by studying the temperature,concentration of toxic and harmful gases and visibility index system of tunnel fire smoke.Through the study of smoke spreading and diffusing law of different smoke control methods in tunnel,it is concluded that the combined ventilation and smoke exhaust has the best smoke control effect,and it is concluded that there is a critical wind speed Vc criterion whether the smoke will reverse in tunnel.The above theoretical analysis method was applied to dafengyakou long distance tunnel.Firstly,the status quo of longitudinal smoke control was numerically simulated and analyzed,and the critical wind speed of longitudinal smoke control scheme was 3.2 m/s when the fire source was located in the middle of the tunnel,and 3.4 m/s when the fire source was located in the side wall of the tunnel.The critical wind speed of longitudinal ventilation can ensure the safety of evacuation to the upstream of the fire source,but the temperature,visibility and CO concentration at the human body characteristic height of the downstream of the fire source exceed the critical value of fire smoke risk factors,which is not conducive to evacuation.In view of the problems existing in longitudinal smoke control,a smoke control scheme of combined ventilation and smoke extraction was put forward.Through numerical simulation analysis,it can be concluded that the smaller the distance between smoke outlets is,the better the fire smoke control effect is.Changing the transverse position of fire source has little influence on the spread of fire smoke.The short side of the smoke outlet(group C and GROUP D in working condition)was arranged along the tunnel longitudinal better than the long side of the smoke outlet(group A in working condition),and the smoke exhaust effect was the best in working condition D3.The theoretical analysis and smoke control optimization scheme in this paper can play a good theoretical guiding role in the current long-distance tunnel fire risk control.Figure[56]Table[14]Reference[78]... |
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