The Research On The Effect Of Ventilation System On Fire Safety Of Underground Garage

Underground garage is a typical flat large space building with low height and large single floor area.There are not only many fire hazards but also large fire loads inside.Once fire occurs,it will endanger the health of personnel,affect the evacuation of vehicles,and even cause serious damage to the building structure and internal pipeline facilities.Therefore,it is extremely necessary to study the control effect of the ventilation system on flue gas,so as to minimize the flue gas temperature,reduce the concentration of flue gas,improve the smoke exhaust efficiency and reduce secondary disasters caused by fir-e.Many scholars at home and abroad have carried out computer simulation and physical model experiments on the development of fire in the flat large space underground garage.In this paper,the previous research contents were firstly summarized,and combined with the current code,the comparison of actual fire cases was made to determine the performance-based fire prevention design for the ventilation system of the underground garage.Then,taking the underground garage of North China University of Technology as the research object,a small-size fire test platform was built,and various working conditions were designed to explore the influence of the location of fire source and the change of air volume on space temperature and CO concentration.Secondly,the FDS numerical calculation model matching the experimental model was established in this paper.On the basis of verifying the reliabilit-y of FDS calculation,the distribution of temperature,CO concentration and visibility in the garage under three kinds of fire source positions and four kinds of air volume were compared,which lays a foundation for selecting the most disadvantageous fire source locations and the optimal air supply.The theoretical formula of maximum temperature rise under ceiling jet is also studied.The relationship between temperature attenuation and fire scale and wind speed is obtained,and the exponential law of temperature attenuation under roof jet is also obtained.Finally,the optimization design of smoke exhaust system is carried out,and a full-scale underground garage model is established in combination with the actual situation.The original specifications such as smoke exhaust height and smoke exhaust direction are reformed.The diffusion of smoke temperature,CO concentration and visibility in underground garage during 4MW fire and the comparison of ignition time of adjacent vehicles are studied.The results show that the increasing exhaust head height and opening the smoke outlet face up can effectively improve the smoke exhaust efficiency,avoid the phenomenon of "suction through",which plays a guiding role in practical engineering.