9.9.4.5. Openings in Exterior Walls of Exits

This Article specifies where any opening has to be protected to reduce the risk of fire breaking out through a window in one fire compartment and exposing the window openings in an exit stairway to sufficient heat to break ordinary glass, rendering the exit unsafe.

Windows in the exterior wall of an enclosed exit can be exposed to fire from windows in an exterior wall of another part of the building. Windows in the same plane as the exit windows are not considered to be an exposure hazard. Windows at an angle of less than 135° located within 3 m (9 ft. 10 in.) horizontally and less than 2 m (6 ft. 7 in.) vertically to each other are considered a hazard (NBC Article 9.10.12.3.). For this reason, either openings in exterior walls of an exit or openings in adjacent exterior walls of the building must be protected with wired glass or glass block (Figure 9.9.-4).

Quoted from Illustrated Users' Guide - NBC2015

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