Stair Pressurization is provided to allow building occupants to safely evacuate a building using the stair cases. Fans are provided to supply air into the staircase upon activation of an associated alarm condition. The idea is to pressurize the stairs so no smoke can enter. Precautions must be taken to stop such fans from venting smoke into the stairs. Take for example if the side or roof of a building is on fire, the smoke from this fire will enter the stair case via the stair Pressurization Fans. For this reason, NFPA 92 specifies conditions to stop the fans upon activation of smoke detection in the air supply. Many times this is accomplished by providing duct smoke detectors on the supply fans. Upon activation of this smoke detector, the stair Pressurization Fans will stop, therefore stopping the fans from supplying smoke into the stairs. Fortunately, NFPA 92 also mandates that such fans that were shut down shall be capable of being manually reset via an override feature at the Fire Command Station.
NFPA 92 – Smoke Control Systems
18.104.22.168.1 A smoke detector shall be provided in the air supply to the pressurized stairwell.
22.214.171.124.2 On detection of smoke in the air supply, the supply fan(s) shall be stopped.