In performance-based design, simple calculation method to evaluate the safety from smoke is useful and valuable, not only because designers could perform safety planning by themselves but also officers could confirm the plan easily. However, it cannot be said that a rational simple method exists for the safety verification of fire rooms with smoke extraction system, though the simple method for fire rooms without smoke extraction has already been widely used. This paper proposes a simple calculation method to evaluate the safety from smoke in a fire room with mechanical smoke extraction system. In this method, the evacuation time and smoke filling time are compared and the required smoke extraction rate can be obtained in order to prevent smoke layer from filling down to the critical height for safety. This simple method is validated to be used for actual planning by detailed study.
