13-160-420  Smokeproof towers – Interior smoke shafts.
   (a)   Every interior smoke shaft used in connection with an entrance vestibule or balcony of a smokeproof tower shall be at least five feet wide at every point and shall be open and unobstructed over an area of not less than 50 square feet from its bottom to the sky; provided, however, that such shaft may be covered with a roof if the walls below such roof are open to the outside air on all sides with a total open area of not less than 100 square feet. The smoke shaft shall be separated from all other parts of the building by construction providing fire resistance of not less than four hours. There shall be no openings from the building into the smoke shaft except the required openings from the vestibules or balconies.
   (b)   Should at least two smokeproof towers be provided the interior smoke shaft shall be at least three feet wide at every point and shall be open and unobstructed over an area of not less than 12 square feet from its bottom to the sky. Such shaft may be covered with a roof if the walls below such roof are open to the outside air on all sides with a total open area of not less than 24 square feet. The two smoke shafts shall be separated from all other parts of the building by construction providing fire resistance of not less than two hours. There shall be no openings from the building into the smoke shaft except the required openings from the vestibules or balconies. The interior surface of the smoke shaft shall be noncombustible material and the corridor door shall be a Class C door.
(Prior code § 67-11.6)