Research On The Evacuation Problems Of Metro Station Based On Fire Dynamic Simulation And Crowd Evacuation Simulation

With the fast urbanization in China,the increasing urban population puts forward higher requirements for urban public transportation.With the advantages including land-saving,high speed and punctuality,and large carrying capacity,the metro system has become the focus of the development and construction of public transportation in many cities The convenience brought by the metro system and its large passenger carrying capacity make some metro stations becoming typical crowded place in the city.Most metro stations are located below ground level and are connected to the outside world by limited exits.The environment of an underground metro station is relatively closed.In case of fire,it can be difficult to evacuate the crowd in the station,and the casualties and property losses will be very serious.Therefore,the safety judgment and evacuation methods of metro stations under fire still need to be further studied.In the existing studies,the limited-time value(such as 6min)is used to judge the safety of subway station evacuation,and whether the various onsite environmental parameters such as combustion products and oxygen content have reached the safety-critical value(concentration)within the limited time,thus the safety of evacuation can be judged.However,some stations may not be able to complete the evacuation within the limited time due to the dense crowds and complex structures.In view of this,theoretical analysis,fire simulation,and evacuation simulation are adopted to study the calculation method of required safety evacuation time under the fire condition of a metro station.Also,the cumulative effects of various on-site environmental factors on the evacuated crowd are studied.At last,a new safety evacuation judgment method under the fire condition is proposed.A fire model is constructed based on metro stations with a typical structure.The distribution characteristics and variation rules of important environmental factors on the fire site are studied,and the proposed crowd safety evacuation judgment method is used to analyze the data of the environmental factors.Based on the fire dynamics simulation and crowd evacuation simulation,a new evacuation strategy,in which part of the crowd in the metro station will evacuate downward when a fire happens in the station hall is proposed,and the applicability and effectiveness of the new evacuation strategy were verified.Research work carried out in this paper and the main research results obtained are listed below:1.The fire incidents that occurred in metro stations both at home and abroad are extensively collected,and the occurrence rules and characteristics of fire in metro stations are deeply analyzed.The results show that fire is a common primary or secondary accident in subway stations,and the main causes of serious casualties are the smoke generated from the combustion of combustible materials,all kinds of toxic and harmful gases,as well as the high temperature in the station after a fire happens.2.In consideration of the influence of onsite environmental factors(including smoke height,visibility,temperature,carbon monoxide,and oxygen content)on the human body,the safety evacuation judgment method of the metro station is established.When establishing the safety evacuation judgment method based on temperature,carbon monoxide,and hypoxic environment,the time accumulation effects of these onsite environmental factors on the human body are considered.It means that a fixed safety threshold is no longer used as the basis for the safety judgment of evacuation.Instead,the cumulative effects of various onsite environmental factors on the human body are considered,with the aim to make a more accurate judgment on the feasibility of evacuation.3.Metro stations with a typical structure are selected and fire models are established based on the selected stations.The changes in smoke height,visibility,temperature,oxygen content,carbon monoxide concentration,and other environmental parameters in different fire scenarios(different fire locations,heat release rates,operating state of smoke extraction equipment,etc.)are analyzed.The results show that compared with the fire in the center of the platform or the station hall,fires at the end of the platform or the station hall have greater influences on the evacuation environment of the station,and the environmental factors at the scene after the fire are more unfavorable to the evacuation of the crowd in the station.The smoke height,temperature,carbon monoxide concentration,oxygen content,and visibility on the platform have no significant change after a fire happens in the station hall.4.Evacuation models in the metro stations with the same structure、dimensions and layout of the fire models are established according to its crowd composition,crowd density.For each area in the metro station model,the influence of the average visibility calculated by the fire model on the speed of crowd evacuation is introduced into the evacuation model,which aims to accurately calculate the required safe evacuation time(RSET).Based on the proposed safety evacuation judgment method and the data of onsite environmental factors in the station calculated by the fire model,the feasibility of safety evacuation in a typical fire scenario is evaluated.5.When a fire happens in the station hall,the smoke diffusion path is the same as the regular outward and upward evacuation path,which may have a negative influence on the safe evacuation of people in the station.A new evacuation strategy,in which some people are evacuated downward under the condition of station hall fire as an auxiliary evacuation method is proposed.The feasibility of part of the passengers evacuate downward to the platform and then leave the fire station by train is studied.By means of numerical simulation based on FDS,the variation of temperature,the concentration of harmful gas,and smoke height with time in the metro station are calculated under the condition of different station hall fires scenarios.Also,the RSET for the studied metro station is calculated by evacuation models.At last,by the proposed safety evacuation judgment method,the feasibility of downward evacuation for the crowd is analyzed according to the data of fire products,and the calculated RSET.6.Tiyu Xilu Metro Station is selected for the field application of the downward evacuation mode for some people under the fire in the station hall,as well as the judgment method of safety evacuation.Fire models and evacuation models are established based on Tiyu Xilu Metro Station.Based on the calculation data of the models,the safety and feasibility of upward evacuation and downward evacuation for some people in Tiyu Xilu Metro Station are analyzed and judged by the proposed safety evacuation judgment method.The results show that when certain conditions such as smoke exhaust capacity and train schedules can be meet,the crowd in the station can finish the evacuation in a shorter time when the downward evacuation mode is applied when the fire happens in the station hall.Thus people will be in a safer condition when compared to the regular upward evacuation mode.