Every standard fireproof vault shall have a vent flue or window opening directly to the outer air. Such vent flue termination or window shall be located not less than ten feet measured vertically or five feet measured horizontally from any fire door or fire window, or not less than 20 feet measured vertically, or ten feet measured horizontally, from any unprotected opening. Such window or vent flue shall have a net open area of not less than five percent of the total wall area in the standard fireproof vault. Nothing in this chapter shall be construed as prohibiting on each floor, vent shaft connections from standard fireproof vaults into one vent shaft; provided, however, that not more than four such vaults on any one floor shall be connected to one such vent shaft. The area of the combined vent shaft shall be of such area as is required to vent the largest of the standard vaults for which said vent shaft provides ventilation. All vent flues or portions of vent flues shall have no inclination from the horizontal of less than 45 degrees. Nothing herein shall be construed as preventing more than one window or vent flue or combination of windows or vent flues to provide the necessary ventilating area. Any such vent flue shall be used for no other purpose than to provide ventilation from standard fireproof vaults. Such vent flue shall be constructed of brick, tile or concrete walls not less than four inches in thickness, and no combustible material shall be used in the construction or support of flues. Any vent flue opening in a standard fireproof vault shall be in the ceiling or as close as practicable to the ceiling. The unobstructed opening into the atmosphere shall be not less in area than the area of the vent flues. Every vent flue furnishing the required ventilation shall be equipped with not less than a 60-minute fire-resistive door which shall be held normally closed, and such fire door shall have as its actuating mechanism a thermostatic releasing device to open the door. Such a door in the vent flue shall be so arranged that when the door is opened, the entire required area of the vent flue shall be available for ventilation purposes. All required windows shall be so provided with thermostatic releasing devices that a fire or an explosion in the vault shall cause such windows to open for the entire required ventilation area.
(Prior code § 129.1-32)