D.C. Mun. Regs. tit. 12, r. 12-E304
Strike Section 304.11 of the International Mechanical Code, but keep the Exception therein, and insert a new Section 304.11 into the Mechanical Code in its place to read as follows:
Guards. Guards shall be provided where various components that require service and roof hatch openings are located within 10 feet (3048 mm) of a roof edge or open side of a walking surface and such edge or open side is located more than 30 inches (762 mm) above the floor, roof or grade below. The guard shall extend not less than 30 inches (762 mm) beyond each end of components that require service and not less than 30 inches (762 mm) beyond each end of the roof hatch opening. The top of the guard shall be located not less than 42 inches (1067 mm) above the elevated surface adjacent to the guard. The guard shall be constructed so as to prevent the passage of a 21-inch-diameter (533 mm) sphere and shall comply with the loading requirements for guards specified in the International Building Code.
D.C. Mun. Regs. tit. 12, r. 12-E304