Experimental study on safety full-scale of tunnel fire disaster under different blocking conditions

In order to study the fire risk of tunnel under blocking conditions,a branch of tunnel network was chosen as the experimental field.The axial flow fan was used for ventilation,and the rated ventilation rate was 27 m 3/s.Taking methanol pool fire as fire source,the heat release rate of fire source is 0.25,0.50 and 1.00 MW respectively.The full-scale experiment was carried out by changing the heat release rate of fire source and the opening and closing mode of air door.The smoke diffusion law of tunnel fire under different blocking conditions was studied by analyzing the parameters of air speed profile of fire source cross section,air speed profile of vertical section in tunnel centerline,excess ceiling temperature along tunnel and excess temperature profile of vertical section in tunnel centerline.The air door control mode is obtained to suppress the fire risk of tunnel.The results show that:① in tunnel ventilation network,the air speed gradually tends to be uniform on tunnel section （22 m away from the airdoor）by rectification after the symmetrical air flow passing through the air door.② The air flow attenuation model of tunnel considering blocking ratio is proposed.The model can predict the air loss under the action of tunnel obstruction according to the change of tunnel blocking ratio,and can calculate the air volume loss along the road resistance loss.③ Under the condition of natural ventilation,when the heat release rate of fire source is greater than 0.5 MW,the fire smoke will rise to the ceiling of tunnel rapidly driven by the fire plume,and the ceiling temperature will rise sharply through heat convection,which will have a great damage to the stability of tunnel structure.The air volume through the fire area can be controlled by adjusting the air door,thus optimizing tunnel fire risk control mode.The local wind speed has little influence on the fire risk.When the air volume in the fire area is insufficient,the temperature rise at the eye height is large,which is not conducive to personnel escape and rescue.④ Under the blocking condition,the asymmetric inlet air flow of tunnel section easily causes the air flow structure disorder,which makes the temperature distribution of tunnel fire smoke unstable and dangerous.