Abstract: At approximately 6:30 a.m. on October 11, 1999, Employee #1, working for an insulation contractor was plugging in an extension cord on the penthouse roof of unit #7 at A.E.S/Southern California Edison's compound. Nearby coworkers were preparing to start insulation on the roof. He ducked to avoid an overhead pipe, lost his balance, and fell approximately 10 ft to 12 ft through an unguarded 6 ft by 10 ft roof opening. Employee #1 sustained torn ligaments in his right knee and was transported to Harbor UCLA Medical Center, where he was treated and released. He was subsequently rehospitalized for additional treatment.