Control of thermal-driven smoke flow at stairways in a subway platform fire

Abstract

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.