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4 PROPOSED STRATEGY In lieu of the required 2-hour fire-resistance rating at the north and east exterior walls of BG3H, it is proposed to provide the following: Water Curtain at North and East Exterior Walls: Provide "water curtain' as listed below. The discharge on the interior shall be calculated with the simultaneous demand of the overhead fire sprinkler system as detailed in NFPA 13. North Wall Exterior: Provide closely-spaced sprinklers (water curtain) at 6 ft on-center maximum spacing per NFPA 13. Sprinklers to be 200°F, dry barrel, upright sprinklers installed in the horizontal spray orientation. These sprinklers will be located at the top of the exterior wall, 12 inches away. The discharge of these sprinklers will develop a spray pattern back at the protected wall. North Wall Interior: Provide closely-spaced sprinklers (water curtain) at 6 ft on-center maximum spacing per NFPA 13. Sprinklers to be 155°F, upright or pendant standard spray sprinklers. These sprinklers will be installed within 12 inches of the roof, at 12 to 24 inches from the wall. The discharge of these sprinklers will develop a spray pattern along the protected wall. East Wall Exterior: No protection provided. East Wall Interior: Provide closely-spaced sprinklers (water curtain) at 6 ft on-center maximum spacing per NFPA 13. Sprinklers to be 155°F, upright or pendant standard spray sprinklers. These sprinklers will be installed within 12 inches of the roof, at 12 to 24 inches from the wall. The discharge of these sprinklers will develop a spray pattern along the protected wall. Non-Combustible Construction with Fire-Resistance-Rated Doors: Although the non- combustible north and east exterior walls are not constructed as a fire-resistance-rated assembly, the doors provided are self-closing, with a 90-minute fire-resistance rating. Sprinklers: The building is fully-sprinklered per NFPA 13 and the requirements of OSSC 412.3.6 Exception 2 which allows for a minimum sprinkler density of Extra Hazard Group I in lieu of foam suppression, when other building area, yard, and aircraft limitations are met. 5 EQUIVALENCY EVALUATION The installation of closely-spaced sprinklers (water curtain) provides "active" protection in lieu of, and equivalent to,the"passive" protection afforded by the use of a fire-resistance-rated assembly. The sprinklers act to cool the surface of the wall to prevent fire from progressing for the same duration. At the north wall, the sprinklers are provided on both sides since there is risk of fire from the building itself, as well as from the property to the north. However, on the east side, protection is only provided at the interior side, for a fire that originates on the interior of the building. The risk of a fire originating from the east is negligible because it fronts a public way with a major street; there are no structures,trees, or significant combustible loading in this area. In addition, per OSSC ( Section 412.3.1 in the 2018 IBC Commentary, the purpose of the 30 ft requirement is to prevent the spread of fire to"adjacent building and structures"and to allow the "fire department additional time and protection as it attempts to take control of a fire situation in a hangar". The condition at this property is such that the associated east yard is -26 ft, with the remaining 4 ft falling on a