Study On Fire Characteristics And Smoke Law Of Tunnel In High Altitude Area

Highway tunnel fire issue is the point of fire discuss.With the proportion of high altitude tunnel increasing year by year,and the focus of fire research is shifting to high altitude tunnel fire.The low pressure,low temperature and low oxygen environment characteristics in high altitude areas will affect the fire combustion characteristics and flue gas rule,so it is of great significance to master the real high altitude tunnel fire environment to the fire theory expansion and emergency rescue.Taking the tunnel structure of Xuefeng Mountain Highway in Hunan province,for 15 MW medium fire,FDS numerical simulation software is used to construct 10 kinds of fire scenarios with different ventilation systems at different altitude from 0m to 4000 m,and the law of tunnel flue gas is qualitatively analyzed,and quantitatively studied.The study results show that the following:(1)The higher the altitude,the faster the longitudinal free spread speed of fire smoke,and the speed difference of smoke spread at different elevations is diminishing over time.The hanging height of flue gas will also be affected by the altitude,the higher the altitude,the lower the smoke layer is,and the risk of fire is increased.The empirical formula of the quadratic function of the correlated altitude can better predict the longitudinal decay distribution of the tunnel smoke layer thickness at different elevations(2)The tunnel fire temperature is also affected by the altitude.The higher the altitude,the temperature is increasing,and the influence of altitude and ventilation mode on temperature is coupled.The empirical formula of the counterproportional function directly related to the altitude can better predict the longitudinal decay of the arch temperature when the tunnel adopts different ventilation methods at different elevations.(3)The higher the altitude,the CO concentration increases in the same time and increases at human body characteristic height position.CO concentration is also affected by ventilation mode,mechanical ventilation tunnels is lower compared to natural ventilation tunnels.(4)Peak temperature of tunnel vault varies greatly with different ventilation system.Longitudinal flow can greatly reduce peak temperature and reduction effect is constantly decreasing with the elevation.At the same time,longitudinal flow will It also affect the distribution and stratification of smoke layer,location of the highest temperature,the longitudinal temperature distribution of vault and environmental conditions of human body characteristics height position.In addition,disaster factors such as temperature,visibility and CO concentration at different locations of tunnel are not synchronized,visibility may be normal but CO concentration may exceed the lethal amount.