Numerical Simulation Of Fire Smoke Characteristics In Island Type Subway Stations

Since the subway stations are mostly buried underground and carry the great part of the city traffic,with complex facilities and structures,and limited communication with the outside world.Once a fire occurs at the station,high-temperature smoke has a major threat to the safety of passengers and workers.Therefore,studying the smoke characteristics in public areas of a station during fires has important reference significance for the designers to optimize the design of the ventilation and smoke exhaust system of the subway station and to formulate safety evacuation measures.In addition,the platform stairs and the entrances and exits of station hall are the joints between different parts of the station and also the main escape routes for personnel in the fire.Therefore,researching the influence of the structural characteristics of the key parts on the safety evacuation parameters of a fire is also the focus of many scholars.Basing on this study,the minimum time required for personnel to escape safely a fire from the station platform or station hall can be calculated separately.After investigation,Xi'an subway stations are mostly island platform with a high degree of structural similarity.Taking a station in Xi'an Subway Line 6 as a prototype,the smoke competition between the entrance and exit of the station and the flue,smoke characteristics in public areas and corridors are simulated and analyzed on different fire conditions by analyzing the smoke propagation characteristics,the changes of temperature field,CO concentration field,visibility and height of smoke layer in each fire condition,such as fire source locations,fire source powers,stair forms,and grades of slopes in a subway station,using the Pyrosim software based on BuildingInformation Modeling(BIM)technology.The rationality of the numerical simulation can be verified by the degree of fit of the reduced-size or full-scale experimental data with the simulated data.The results of this study show that:(1)For platform fires,when the fire source power is the same,it is the most unfavorable to the safety of evacuation of passengers when the fire source is located between the two stairs.Once a fire occurs at the station the evacuation environment is different in each area of the platform,the evacuation safety index of the fire source area was exceeded firstly,followed by the end of the platform,and the evacuation environment near the exit of the stairs is better.As for the two forms of the platform staircase,the central staircase has a larger and safer resting platform,which can take more people to evacuate.Considering that the escalator is out of service during the fire,calculating the hourly peak passenger flow during the summer of 2042,the time taken by the passengers to evacuation from the station platform to the station hall during the fire at the station is 4.39 min.(2)For the fire at the station hall,in the condition of natural exhaust smoke or mechanical exhaust fan can not meet the full discharge of smoke from the station hall,the smoke gushing out of the ground from the northeast,southeast,and northwest entrances and exits,and cannot be discharged heavily from the two entrances and exits at the same time based on the particularity of the entrance and exit of this metro station.The increase in gradient of the entrance and exit stairs will not only improve their own smoke competitiveness,but also affect the entrance and exit passages on the same side.Similarly,taking into account the escalator outage,calculating the hourly peak passenger flow during the summer of 2042,the time required for the evacuation of station personnel from the southwest,southeast,northeast,and northwest directions is7.39 minutes,6.60 minutes,6.49 minutes,and 6.49 minutes respectively.