Although there is no record of large loss of life in fires in high buildings, the increasing number being erected makes it desirable that the provisions for safety to life be reconsidered. It is now becoming evident that in the event of fire in a lower storey of a hig11 building, all vertical shafts will probably become filled with smoke, due to the buoyancy effect that induces vertical movement of air and smoke. This has been discussed in recent papers from the Division of Building Research (1, 2, and 3). Complete reliance can no longer be placed on immediate evacuation, or upon the concept of stairways as a place of safety in high buildings. Other factors in the building design will increasingly Iw.ve to be brought into play to increase the degree of safety of the occupants. When considering the various measures that can influence safety it is always desirable as a first step to predict the time that is needed to evacuate a building. This forms the subject of this paper.