Smoke migration as a result of fire can contaminate elevator and stair shafts, posing a serious threat to fire fighters and occupants, particularly in high-rise buildings where the time for evacuation can be long and the fire must be fought from inside. Measures to prevent smoke contamination of elevator and stair shafts, therefore, are an essential part of the over-all fire protection system for high-rise buildings.

Pressurization of a shaft is one means of maintaining it tenable during a fire. This involves increasing the pressures inside the shaft above those of adjacent floor spaces by injecting outdoor air into the shaft with a supply fan. The direction of air flow would then be from the shaft to the floor spaces, preventing the smoke generated by a fire from migrating into the shaft. The air supplied to the shaft not only assists in preventing smoke entry but also helps to dilute smoke which might have migrated into the shaft prior to activation of the pressurization system of when several shaft doors are opened during evacuation and fire fighting.

There are various approaches to the design of pressurization systems, but in all design a knowledge of the air tightness of the shaft walls is needed to calculate the supply air rate needed to achieve the required level of pressurization. Such information is not readily available at the present, and hence, a research project was undertaken to obtain air leakage values of the walls of elevator and stair shafts. In addition, the pressure loss characteristics of stair shafts were determined, as the flow resistance of the winding staircase can have a significant effect on the vertical distribution of pressurization.

The elevator and stair shafts of eight multistory building ranging in height from 9 to 22 stories were tested, and the results are herein reported.