Research On Smoke Suppression Technology In Subway Platform Based On Ultra-fine Water Mist

With the modernization of the city,the subway as a convenient means of transport brings convenience to the people of the city.However,subway fire accidents have occurred from time to time,which seriously threatens people’s lives.Studies have shown that the high-temperature smoke generated by the fire is the main factor leading to the casualties.The platform is generally located at the bottom of the subway space,which environment is closed and the heat dissipation conditions are poor.When the fire occurs in the platform space,the smoke gas spreads in the interior and flows upwards through the stairwell,which brings many unfavorable factors to the evacuation of people.The traditional methods of smoke prevention and smoke exhaust mainly use the ventilation strategy to control the smoke gas.However,with the advancement of technology,people have put forward higher requirements for smoke gas control.Studies have shown that ultrasonic atomization can produce water mist droplets with size of less than 50μm and confirms that it has great potential in the field of fire protection.In this paper,the experimental study on the smoke restraining effect and temperature characteristics of platform space under ultra-fine water mist is conducted.This provides some reference value for ensuring that the escape personnel are not scalded by smoke.Based on the analysis of the spatial structure of common subway stations,a subway platform fire test model is established.Ultrasonic atomization technology was used to design an ultrafine water mist generating system.A series of K-type thermocouples were arranged inside the subway platform to research the characteristics of fire smoke.The horizontal distribution of fire smoke temperature under the ceiling and the height of the smoke layer at the exit of the stairs were studied.The results show that ultrafine water mist can efficiently reduce the temperature of smoke gas.The horizontal distribution of smoke gas temperature can be divided into two areas: the temperature decay zone and the temperature stability zone.The smoke gas temperature in the temperature decay zone rapidly decays,and the smoke gas temperature in the temperature stability zone approaches the ambient temperature.The ultra-fine water mist has little effect on the height of the smoke gas layer at the exit of the stairs.The factors such as the amount of atomization,the speed of the driving airstream,the time of applying the mist,and the location of the fire source were investigated.The results show that during the process of increasing the atomizing amount or the driving airflow velocity,the highest smoke temperature decreases and the longitudinal temperature decay trends becomes slow.The speed of the drive air flow also related to the range of the temperature decay zone.When the air flow velocity is greater than 1.0 m/s,the range of the temperature decay zone no longer decreases.The time of applying ultrafine water mist at the early stage of combustion show better restraining effect,but at the stable stage of smoke development has no obvious effect on the temperature.When the distance between the fire source and the ultra-fine water mist inlet is shortened,the maximum temperature of the smoke gas decreases.Also,ultra-fine water mist has a barrier effect on the diffusion of smoke.By setting local cylindrical obstacle in the platform space to study the ultrafine water mist restraint effect under the presence of obstacles.The results show that the ultra-fine water mist can also restrain fire smoke and does not change the height of the smoke layer.However,the restraining effect is weakened due to the presence of obstacles.Compared with the case of no obstacles under the same conditions,the smoke temperature in the temperature decay zone are increased.Increasing the amount of atomization or the speed of the drive air can reduce the effect of obstacles.The influence of the position of the local obstacle on the smoke temperature horizontal distribution can be ignored and the maximum temperature of the smoke gas at the exit of the stairs is increased.