This paper is based on findings resulting from ASHRAE Research Project RP-1447.

The National Research Council of Canada (NRC)conducted full-scale fire experiments to investigate whetherpressurecompensatingsystems areneededto maintain tenableconditions within pressurized stairwells. Ten tests wereconducted in the NRC 10-story test facility with the stairwellin the facility pressurized. The tests were conducted with thestairwell door on the fire floor closed and selected stairwelldoors on the other floors open. Two fire scenarios with ashielded sprinklered fire and a nonsprinklered fire were testedwith varying number and location of open stairwell doors.

Tenability analyses were conducted with experimental test results to investigate the performance of the pressurized stairwell with and without pressure compensating systems. Without compensating for pressure losses, the pressure difference across the stairwell door on the fire floor decreased considerably with open stairwell doors. However, a noncompensated stairwell remained tenable for 30 minutes as long as the door on the fire floor was closed both for the shielded sprinklered fireandthe nonsprinklered fire scenarios. It is concluded that if the base pressurization system meets the requirement of the design pressure difference with a proper arrangement of air injection points, the stairwell will remain tenable as long as the door on the fire floor is closed for both sprinklered and nonsprinkled fire scenarios used in the tests.