3.2.6.2.Limits to Smoke Movement

(1) A sprinklered building shall be designed in accordance with Sentences (2) to (6) and MMAH Supplementary Standard SB-4, “Measures for Fire Safety in High Buildings,” to limit the danger to occupants and firefighters from exposure to smoke in a building fire. (2) A building referred to in Sentence (1), shall be designed so that, during a period of 2 h after the start of a fire, each exit stair serving storeys below the lowest exit level will not contain more than 1% by volume of contaminated air from the fire floor, assuming an outdoor temperature equal to the January design temperature on a 2.5% basis determined in conformance with MMAH Supplementary Standard SB-1, “Climatic and Seismic Data.” (3) Each stairway that serves storeys above the lowest exit level shall have a vent to the outdoors, at or near the bottom of the stair shaft, that (a) has an openable area of 0.05 m2 for every door between the stair shaft and a floor area, but not less than 1.8 m2, (b) opens directly to the outdoors or into a vestibule that has a similar opening to the outdoors, and (c) has a door or closure that (i) is openable manually, and (ii) can remain in the open position during a fire emergency. (4) Measures shall be taken to limit movement of smoke from a fire in a floor area below the lowest exit storey into upper storeys. (5) Except for exhaust fans in kitchens, washrooms and bathrooms in dwelling units, and except for fans used for smoke venting as required by Article 3.2.6.6., air moving fans in a system that serves more than 2 storeys shall be designed and installed so that in the event of a fire these fans can be stopped by means of a manually operated switch at the central alarm and control facility. (6) Except as provided in Article 3.2.4.12. or where there is a conflict with other smoke control measures in the building, air-handling systems used to provide make-up air to public corridors serving suites in a Group C major occupancy shall not shut down automatically upon activation of the fire alarm so as to maintain corridor pressurization. (7) A building that is not sprinklered shall be designed in accordance with MMAH Supplementary Standard SB-4, “Measures for Fire Safety in High Buildings,” to limit the danger to occupants and firefighters from exposure to smoke in a building fire.