To manage thermal-driven smoke from fires in a subway station, a mechanical ventilation system is usually installed. Such a system normally consists of an air supply system and a smoke exhaust system. In case of a platform fire, the ventilation systems will be activated to control the smoke and to provide better environmental conditions for personnel evacuation. This paper conducted a theoretical analysis and a series of CFD simulations to study the critical velocity (minimum air velocity) at the stairways for preventing smoke propagating from the platform to the upper floor through the stairways in case of a platform fire. Correlations for critical velocities are established for two typical types of stairways (i.e., with and without side slabs). It is found that the critical velocity is well correlated with the heat release rate by a 1/3 power law function for both types of stairways, but it varies with the height of the smoke curtain at the stairway by a 1.375 and a 2.55 power law function for stairways with and without side slabs, respectively. The results may serve as a useful reference for smoke control in subway platform fires.

为了管理地铁站火灾引起的热能烟雾，通常会安装机械通风系统。这种系统通常由空气供应系统和排烟系统组成。在平台起火的情况下，将启动通风系统以控制烟雾并为人员疏散提供更好的环境条件。本文进行了理论分析和一系列的CFD模拟，以研究楼梯的临界速度（最小空气速度），以防止烟雾在平台起火时从平台通过平台传播到上层楼板。对于两种典型类型的楼梯（即带有和不带有侧板），建立了临界速度的相关性。已发现，对于两种类型的楼梯，临界速度均与热释放速率相关，且具有1/3幂定律函数，但其​​随楼梯上烟幕高度的变化分别为1.375和2.55幂定律分别用于带和不带侧板的楼梯。该结果可为地铁车站火灾中的烟气控制提供有用的参考。