(1) Except as required by Sentences (3) and 3.2.3.13. (1) or as permitted by Sentence 3.2.3.19. (4), if an unprotected opening in an exterior wall of a fire compartment is exposed to an unprotected opening in the exterior wall of another fire compartment, and the planes of the two walls are parallel or at an angle less than 135, measured from the exterior of the building, the unprotected openings in the two fire compartments shall be separated by a distance not less than DO,
where,
DO =2D – [(θ/90) × D] but in no case less than 1 m, and
D =the greater required limiting distance for the exposing building faces of the two fire compartments, and
θ =the angle made by the intersecting planes of the exposing building faces of the two fire compartments (in the case where the exterior walls are parallel and face each other, θ = 0).
(2) The exterior wall of each fire compartment referred to in Sentence (1) within the distance, DO, shall have a fire-resistance rating not less than that required for the interior vertical fire separation between the fire compartment and the remainder of the building.
(3) Sentence (1) does not apply to unprotected openings of fire compartments within a building that is sprinklered, but shall apply to,
(a) unprotected openings of fire compartments on opposite sides of a firewall, and
(b) exposure from unprotected openings of a fire compartment that is not protected by an automatic sprinkler system.