Abstract: Employee #1 was installing single ply rubber roofing material on an office building roof that contained 17 unguarded/uncovered openings for air conditioning installation. Each was surrounded by a metal frame that extended 12 in. above roof level. Employees had rolled out a 100 ft length of rubber on the front portion of the roof and were preparing to spread it out to its full width. Four or five employees, including Employee #1, had stationed themselves along the length of the rubber and begun pulling it out to unfold it. The employees were facing the front of the building while backing toward the roof openings. Employee #1's leg apparently struck the raised metal frame, causing him to fall backward through a 27 in. by 39 1/2 in. opening. He fell 20 ft to a concrete floor, sustaining massive head injuries, and died.