The pressurization smoke control system for vestibules, stairwells and corridors has been popularized. In order to plan the system, it is essential to grasp the relationship between the characteristic of smoke and air velocity to prevent smoke from spreading. An experiment on the effect of soffit in a corridor and air velocity to prevent smoke flow was carried out. The relationship between the characteristic of hot gases and velocity of air stream to prevent smoke flowing back was clarified by the experimental results and the theoretically supposed relation between buoyancy of hot gases and inertia of air stream.
