Study On Smoke Movement Characteristics Of Arch Subway Station

Subway is an important means of public transportation in many cities.The increasingly perfect subway transportation network has brought a lot of convenience to the citizens.With the development of underground rail transit in China,the number of subway stations is increasing,and the structure forms are also innovative.At present,there is a new structural form of subway station--arched subway station hall without column net.The dome subway station hall is simple and beautiful,which can be arranged as a special artistic attraction.But at the same time,arched subway hall also brought some new problems to fire prevention and control.According to statistics,the casualties of fire accidents are mainly due to the toxic and harmful high temperature smoke brought by combustion.Therefore,it is of great significance to study fire smoke movement characteristics and fire smoke control methods in subway fire prevention and control.In this paper,the smoke movement characteristics and control of arch subway fire are studied by combining theoretical analysis and numerical simulation.The specific research work is as follows:Based on the theoretical analysis of smoke layer settlement,a model program for smoke spreading area of fire in arch-shaped subway station is written to study the change of smoke settlement height with time under different mechanical smoke emission.The research shows that with the increase of smoke exhaust volume,the settlement speed of smoke layer slows down.When the smoke exhaust volume is 28.4 m~3/s,the smoke layer reaches the height of overflow outlet about 360 s.The program was further modified to adapt to the process of flue gas settlement of flat-roofed buildings,and the effects of heat release rate,building height,building area and smoke exhaust volume on the flue gas settlement time were studied.The prediction model of flue gas settlement time was obtained through dimensionless analysis.Through the method of numerical simulation of fire dynamics software FDS,five typical fire source positions were simulated to study the smoke movement characteristics of different fire source positions in arch-shaped subway station.Based on the results,it is discussed that the most unfavorable fire source location is the most unfavorable fire source location for evacuation of station personnel.The study shows that when position A is on fire,the smoke spreads widely,the settlement speed is faster,and the visibility decreases lowest in most areas.Fire source location A is the most unfavorable fire location in the station hall,and its smoke spreading characteristics pose the greatest threat to personnel evacuation.When location A occurs fire,"smoke congestion"occurs in the area near the entrance and exit passageways.Visibility is the lowest in the area near the entrance and exit passageways,and the smoke settles in the area near the entrance and exit passageways at the earliest.By means of numerical simulation of fire dynamics software FDS,three different types of combustible materials are simulated to study the smoke movement characteristics of different types of combustible materials in arch subway station.According to the results,it is discussed that a certain type of fuel is the most unfavorable to the evacuation of station personnel--the most unfavorable type of fuel.The results show that the temperature and CO concentration at a height of2 m above the station hall do not have much influence on the evacuation of personnel,and the main influence of smoke on the evacuation of personnel is visibility.Compared with kerosene and polystyrene fires,polyurethane fires have the lowest visibility at a height of 2 m,which has the greatest impact on evacuation.The influence of different smoke exhaust modes,smoke retaining vertical wall height and smoke exhaust volume on visibility of subway station hall was studied by FDS numerical simulation.The research shows that the side smoke outlet should be arranged as high as possible near the ceiling.The increase of smoke exhaust volume can effectively improve the visibility at 2m height of station hall,but the increase of mechanical smoke exhaust volume to 85.2 m3/s still cannot make the visibility of all areas at 2 m height of station hall more than 10 m.In addition,when the exhaust volume exceeds 42.6 m3/s,the exhaust port will be sucked through and the exhaust efficiency will be reduced.When the 1.0 m height smoke retaining vertical wall and mechanical smoke exhaust volume of 42.6 m3/s work together,the visibility of all areas at a height of 2 m in the station hall can be greater than 10 m.The smoke control effect can be optimized when smoke retaining vertical wall and mechanical smoke exhaust work together.In this paper,the influence of different mechanical smoke exhaust volume and smoke retaining wall on the available evacuation time was studied by FDS numerical simulation.Then Pathfinder evacuation simulation software is used to calculate the necessary evacuation time for different numbers of people in subway stations.The number of people who can be safely evacuated can be obtained by comparing the necessary safe evacuation time and the safe evacuation time.The results show that the time of safe evacuation increases with the increase of mechanical smoke emission.When the mechanical smoke emission is 42.6 m3/s,2000 people can be safely evacuated under the smoke retaining wall condition,and 1000 people can be safely evacuated without the smoke retaining wall condition.When smoke retaining wall and mechanical smoke exhaust work together,more people can be evacuated safely.