Study On The Influence Of Smoke Exhaust Vents On Fire Smoke Characteristics Of Subway Stations

With the continuous development of urban subways,the subway has become the busiest and most efficient urban transportation tool in the world,bringing great convenience to people’s travel.However,the subway is often underground.Due to its complex structure,insufficient natural ventilation,and dense passenger flow,once a fire occurs,it is very easy to cause serious casualties,property losses,and social impacts.Studies have shown that casualties in subway fire accidents are mainly due to the inhalation of a large amount of toxic and harmful high-temperature smoke.Therefore,when a fire occurs in a station,the smoke outlet in the mechanical smoke exhaust system of the station is generally used to discharge high-temperature smoke in time.Therefore,studying the effect of the smoke outlet on the smoke characteristics of subway station fires has important theoretical guiding significance for the safe evacuation of personnel.A subway double-deck island station was chosen as the research object;the fire source power was 2MW.Pyrosim fire simulation software was used to establish a full-scale physical model,and carried out numerical simulation research and analysis on the following:(1)In the event of a fire on a platform,assumed that the fire source was set at a position 5m away from the end wall of the platform,and kept the height,wind speed and spacing of the exhaust vents unchanged.Researched and comparative analysis of flue gas characteristics.The results show that in the event of a fire on the platform,the mechanical exhaust effect is better when the exhaust outlet is located at the top of the exhaust duct;(2)In the event of a fire in the station hall,supposed the fire source of the station hall was set in the center of the station hall,and the height,wind speed and spacing of the smoke outlets were kept unchanged.Researched and comparative analysis of flue gas characteristics in the hall.The results show that in the event of a fire in the station hall,the mechanical exhaust effect is better when the exhaust outlet is located at the top of the exhaust duct;(3)The fire source of the platform was set at a position 5m away from the end wall of the platform.In the event of a fire,kept the wind speed and spacing of the top smoke outlet unchanged,and changed the height of the top smoke outlet Z(Z=3.4m,3.6m,3.8m,4m),researched and comparative analysis of the influence of the change of the height of the top smoke outlet on the characteristics of the smoke;(4)The fire source of the platform was set at a position 5m away from the end wall of the platform.In the event of a fire,kept the height,wind speed and spacing of the smoke exhaust vent unchanged,and studied the horizontal distance between the top smoke vent and the outer wall surface of the platform screen door d(d= 0.6m,0.8m,1m)influence on flue gas characteristics;(5)The fire source of the platform was set in the center of the platform.In the event of a fire,the combined arrangement of the top smoke outlets was studied as two non-uniform arrangements of "close on both sides,sparse in the middle","sparse on both sides,dense in the middle" and uniform arrangement.The influence of the three kinds of exhaust outlets’ combined arrangement on the downward wind speed at the connecting stairs of the platform and station hall was studied.The results are obtained by numerical simulation and comparative analysis of the temperature and CO concentration distribution at the ceiling height of the platform and the station hall;the spread of smoke;the visibility and temperature at the characteristic height of the human eye and the distribution of CO concentration.The following conclusions:(1)The smoke exhaust port is located at the top of the smoke exhaust pipe,and the smoke exhaust effect is better;(2)The increase in the height of the top smoke outlet helps to improve the effect of mechanical smoke exhaust.When the height of the smoke outlet on the top of the platform is 4m,the mechanical smoke exhaust effect is better;(3)When the horizontal distance between the top smoke outlet and the outer wall surface of the platform screen door is d =0.6m,the mechanical smoke exhaust effect is better;(4)When the top smoke outlets are arranged in a non-uniform combination arrangement of "sparse on both sides and dense in the middle",the downward wind speed at the connecting stairs of the platform and station hall can be increased,which is conducive to evacuation.