If any equipment or appliance requiring access is installed on a roof or elevated structure at a height exceeding 16 feet (4877 mm) above grade plane, a permanent approved means of access shall be provided, and shall extend from grade or floor level to the surface space of the equipment and appliance. Such access shall not require any person to climb over obstructions greater than 30 inches (762 mm) high or walk on roofs having a slope greater than 4 units vertical in 12 units horizontal (33-percent slope).