Study On Smoke Flow And Evacuation Of Fire In Subway Section Tunnels

With the continuous increase of urban population,the popularity of subway has brought great convenience to people.But on the other hand,the safety has been of concern.For example,it is difficult to evacuate the public when there is a fire disaster due to the closed and narrow subway tunnel,which would toughen the smoke exhaust and reduce the visibility.Therefore,it is of great significance to study the smoke movement and personnel evacuation in the subway in the case of fire.In addition,it provides a reference for smoke control and fire-fighting in the tunnel fire.In this thesis,firstly,the distribution of longitudinal ventilation velocity in subway tunnel has been studied under the blockage condition based on a model experiment and the numerical simulation.Secondly,taking a subway tunnel as the object,the temperature,the CO concentration and the visibility in the ballast bed,the evacuation platform and the subway has been separately simulated and analyzed under the conditions of natural and mechanical smoke exhaust by the Pyrosim software.On this basis,the best strategy of the personnel evacuation has been found based on the simulation by Pathfinder software.The main conclusions are as follows:(1)Accroding to the experimental data,it can be concluded that there are regularities for the variation trend of wind velocity along the tunnel.First of all,though the fluid would have a frictional resistance loss when it flows in the tunnel,there is a significant increase for the wind velocity at the end of the blockage,and little change in the obstructed segment,which indicates that the blocking effect increases the wind velocity.Therefore,when a train is stuck in an interval tunnel,the blockage effect will make the wind velocity increased due to the large ratio between the subway and tunnel.By comparing the experimental data and simulation data,it can be found that the variation trends of wind velocity are identical,and the value of numbers are almost the same,which verifies the experimental correctness and the reliability of the numerical simulation,and provides a reference for numerical simulation of subway tunnel fire and for the selection of critical velocity in mechanical smoke exhaust.(2)Under the condition of natural smoke exhaust,the smoke is distributed symmetrically centered on the fire source.On the ballast bed,the personnel are not affected by the temperature and the CO concentration,but affected by the visibility,and the hazardous areas range between 300 m to 70 m downstream and between 70 m to 300 m upstream of the fire source.In the subway,the personnel will be affected by the temperature,the CO concentration and the visibility,and the hazardous area affected by the three factors ranges between 55m downstream to 55 m upstream.On the evacuation platform,the hazard areas affected by the temperature,the CO concentration and the visibility separately range from 55 m downstream to 55 m upstream,220 m downstream to 220 m upstream and 300 m downstream to 300 m upstream of the fire source.(3)Under the condition of mechanical smoke exhaust,when the wind velocity approached to the critical value,on the ballast bed,the personnel are only affected by the visibility,and the hazard area ranges from 300 m to 70 m downstream of fire.In the subway,the CO concentration will only pose a threat to personnel around the fire and at the ends of the subway,the areas affected by the temperature and the visibility separately range between 55m downstream to 10 m upstream and between 55 m downstream to 55 m upstream of the fire.On the evacuation platform,the temperature will only pose a threat to personnel located on the 10 m downstream of the fire;The CO concentration would not cause damage to the personnel;the hazard area affected by the visibility ranges between 300 m to 10 m downstream of the fire.(4)The safe evacuation time of the personnel affected by temperature,CO concentration and visibility is equal to the time that reaches the critical risk condition with the natural and mechanical smoke exhaust.And then,by the comparison between the safe evacuation time and the required safe evacuation time of the personnel,it can be known that the optimal evacuation strategy:under the condition of mechanical smoke exhaust,personnel in the train enter the ballast bed,or first enter the evacuation platform then evacuate from the evacuation platform to the ballast bed by the evacuation ladder 150 from the train center,finally,all of people enter the adjacent tunnel through a contact channel.but the visibility in the tunnel should be ensured when the evacuation strategy is adopted.