Analysis Of Fire Smoke Spread Characteristics And People Evacuation Safety In Long Tunnel

With the continuous acceleration of China’s public highway and railway construction,the length and altitude of public railroad tunnels are constantly breaking new records,while the research on the smoke distribution characteristics and spreading mechanism of fire in long tunnels is still insufficient,the high-altitude environment is also less considered,and the theoretical basis and specifications for the engineering design and disaster prevention and evacuation of high-altitude tunnels are yet to be improved.As a special building with a closed structure,the hazards caused by fire accidents in tunnels are much higher than those in common buildings,so it is necessary to study the smoke distribution characteristics and evacuation safety of long tunnels.In this thesis,the smoke distribution of fires in long tunnels is calculated by numerical simulation with FDS software for LES simulation.The distribution of smoke in 100-500 m tunnels was analyzed,and the smoke distribution characteristics,mass flow rate,smoke layer thickness,flow field,temperature field and velocity field of the grown tunnel were analyzed considering 10-50 MW fire power.It is found that the longer the tunnel length is,the larger the mass flow rate and smoke layer thickness are,and when the tunnel length is larger than 200 m,it shows a trend of growth and then decrease with the fire source distance,and the coupling effect of smoke temperature and velocity is considered to be the reason for this phenomenon.Combined with the increasing number of high-altitude tunnels in China,the diffusion of smoke in grown-up tunnels at 0-4 km altitude was analyzed,and it was found that the mass flow rate decreased with increasing altitude and the thickness of smoke layer increased with increasing altitude.The smoke distribution characteristics and diffusion mechanism of the grown-up tunnel under high altitude environment were analyzed,and the fire source temperature,roof plate temperature and roof plate smoke gas velocity were compared at high altitude.It was found that the fire plume volume sucking cold air mass decreased,the fire source temperature increased,the roof plate temperature increased,and the roof plate smoke gas flow velocity increased at high altitude,and the reasons for the changes were analyzed.From the perspective of reducing tunnel fire losses and casualties,the common methods of ventilation control in grown-up tunnels are discussed,and it is concluded that longitudinal ventilation is the most predominant ventilation scheme used in grownup tunnels.The safety of evacuation under critical wind speed in plain and high altitude tunnels is analyzed,and it is found that the evacuation safety zone is gradually reduced with increasing altitude,and different evacuation strategies should be adopted under different fire power.Finally,numerical simulations were conducted for the critical wind velocity in high altitude tunnels,and the differences between the critical wind velocity in high altitude and plain areas were compared,and it was found that the critical wind velocity in high altitude areas is higher than that in plain areas.