Abstract: At 10:20 a.m. on April 11, 1991, a standard Favco 750 tower crane, serial #100/18, equipment CD2210, was being used to lift a 35 ft long, 2 1/2 ton steel beam. Two ground workers had hooked up the beam using a single 12 ft long Kevlart sling, serial #TPX2000, that was choked with softeners. The load was positioned off center at a 45 degree angle. Targrave 4 in., no. 40 rigging clamps were placed adjacent to the flanges of the beam, which were coated with a corrosive paint. The steel beam was hoisted 40 ft above the roof area when the clamps slipped and the sling came off the beam. It fell into the northwestern corner of the roof, penetrating 9 in. into the 10th floor. No employees were injured.