Duct systems used to move air in air-conditioning, heating, ventilating and exhaust systems shall conform to the provisions of this chapter except as otherwise specified in Articles V, Exhaust Systems and Article 7, Combustion Air.
Exception: Ducts discharging combustible material directly into any combustion chamber shall be constructed of not less than 12 U.S. gauge steel casing and shall be lined with not less than 4 1/2 in. (114 mm) of firebrick (ASTM C27) Type F, medium duty, or the equivalent. The charging hopper shall not exceed 6 ft. (1.8 m) in length, measured from the floor opening to the outside of the roof of the incinerator combustion chamber.
The charging opening shall be protected by a cover extending beyond the edges of the opening for at least 2 in. (51 mm) on all sides and lined with at least 2 1/2 in. (63.5 mm) of refractory material.
The charging floor opening shall be located in a room with walls and floor and ceiling assemblies having a fire resistance rating of at least 2 hours, with openings protected by approved self-closing or automatic-closing 3-hour fire doors suitable for Class A openings. Such doors shall be kept closed during the charging operation and at other times, except when waste material is delivered to the room.