The greatest hazard to the occupants of a burning building is smoke. There are more deaths from the effects of smoke and toxic gases than from the direct effects of flame. Smoke can obscure vision and hide the exit signs, and toxic gases can ~uickly affect the senses and render a person unable to reason correctly. Additionally, irritating gases can cause choking and panic.

In multi-story buildings smoke tends to spread upwards through the building's stair shafts, elevator shafts, and duct shafts. Since the stair shafts are the primary means of evacuation from these buildings, the movement of people from the burning building is of great concern. In hospitals the problems are particularly acute due to the restricted mobility of the patients. In addition, the many building services, such as laundry chutes, trash chutes, vertical conveyors, transport systems, and elevators, provide additional passages for the travel of smoke. While the more hazardous areas are protected by automatic sprinklers, it has been found that there is a significant amount of smoke released before the sprinkler heads are actuated, We have had instances where fires in basement trash rooms have caused injury to patients on the top floors of a hospital.

The life safety code re~uires that hospitals be compartmented into individual fire and smoke zones using fire resistant walls and partitions. Doors in these barriers usually are provided with magnetic door holders which will deactivate when the smoke detector senses smoke. This theory of compartmentation is widely used, but its effectiveness as a smoke barrier has never been ade~uately tested.