The Ontario Building Code | Exits
(1) A building that is more than 18 m in height, measured between grade and the floor level of the top storey, and that contains an interconnected floor space, shall be designed to limit the passage of smoke from a fire into exitstairshafts opening into an interconnected floor spaceso that during a 2 h period after the start of fire, such stairshafts will not contain more than 1% by volume of contaminated air from the fire floor, assuming an outdoorref ="http://thehandyforce.com/doors/" title ="Toronto Door installer">door temperature equal to the January design temperature on a 2.5% basis.
(2) Where a building containing an interconnected floor space is more than 75 m in height, measured between grade and the floor level of the top storey, the exitstairshaft protection required in Sentence (1) shall be accomplished by the provision, between each floor area and each exit stairshaft, of a vestibule provided with a mechanical air supply or with a vent opening to the outdoors.
(3) Where a vestibule protecting an exitstairshaft is incorporated into the design of the buildingto meet the requirements of Sentence (1) or (2), such vestibule shall,
(a) be designed so that each doorway for a door opening into the vestibule is located at least 1 800 mm from a door or doors opening outward from the vestibule,
(b) be separated from the remainder of the floor area by a fire separation having a fire-resistance ratingat least equal to that required for the exit that it serves except that the fire-resistance rating of a fire separation between the vestibule and a public corridor need not exceed 45 min, and
(c) not have a door or doors opening into more than one exit stairshaft.
(4) Except where exits serving the floor area are at ground level, the increased travel distance to exits permitted by Clause 220.127.116.11.(1)(c) shall not apply to a floor areawithin an interconnected floor space.
(5) Where a portion of a floor area is not within an interconnected floor space, required access to exit from such portion of a floor area shall not lead through an interconnected floor space.
(6) Except as provided in Sentences (7) and (8), portions of an interconnected floor space that have floor levels more than 18 m above grade shall be served by exits that provide at least 0.3 m2 of area of treads, landings and floor surface for each occupant of such portions of an interconnected floor space.
(7) The requirements of Sentence (6) need not be applied where a floor area that is a portion of an interconnected floor space and that has a floor level more than 18 m above grade is separated from the remainder of the interconnected floor space by a fire separation having a fire-resistance ratingof at least 1 h, except that no fire-resistance ratingis required for such fire separation where all of the major occupancies contained within the interconnected floor space may be classified as light hazard occupancies in conformance with Appendix A of NFPA 13 "Installation of Sprinkler Systems".
(8) The requirements of Sentence (6) need not be applied where the exit stairs that serve interconnected floor spaces are designed so that the required width of each stair is cumulative.