Abstract: At approximately 9:45 a.m. on January 6, 2003, a crew from Brown & Sons Sheetmetal arrived on site where Lawson Roofing was already working. The crew did not check in with the general contractor or sign the daily sign-in sheet. Lawson Roofing had just removed a 0.5 inch sheet of plywood that had been fastened over a skylight opening on the north-east corner of the roof so they could begin their work. This created a floor opening in the roof. The crew from Brown & Sons placed a ladder through the floor opening so they could move their materials up to the roof using the opening. The foreman from Lawson Roofing suggested that they move their ladder away from the opening. After a coworker moved the ladder to the north-west corner, approximately 15 ft away from the opening, the foreman from Brown & Sons moved the ladder back to the opening. The crew began to load their materials through the roof. One employee was observed straddling the opening during this operation. He fell through the opening approximately 15 to 20 feet and received serious cuts and injuries to his left arm, shoulder and forehead. He was transported to S.F. General Hospital due to his injuries.