Abstract: On November 17, 2005, Employees #1 and two coworkers were at a two-story school building that was under construction. The coworkers were on the roof, using an acetylene torch to cut a hole in the metal decking in preparation for running a radon gas pipe through the roof. They had used the torch throughout the day to cut several holes, but approximately ten minutes before the accident, the torch began to malfunction. The oxygen levels being fed through the rig were insufficient to allow the torch to burn hot enough to cut normally. Employee #1, the foreman, waited on the second floor for several minutes, but when his coworkers had not begun the cut, he went up to the roof to investigate. He helped the coworkers determine why the torch was not operating normally; they soon managed to get the torch lit and hot enough to burn the hole, even though the oxygen level was still too low to burn as hot as normal. Employee #1 then sent one of the coworkers to the opposite side of the roof where they had previously cut another hole to retrieve a piece of 6 in. pipe to check the size of the new hole. Using this measure, they found that the new hole needed to be larger. Employee #1, who had made the initial cut, picked up the torch rig, held it away from the hole and lit it. He and his coworkers were kneeling next to the hole and he was bringing the torch in to make another cut when an explosion occurred, knocking all three workers backward. Employee #1's full face shield was blown off his head and landed on the ground about 50 to 60 ft from the building. He sustained minor lacerations to his head and face, contusions to his left eye, blurred vision, and temporary hearing loss. Employee #1 was transported to the Washington Hospital Center's Medstar Burn Center, where he was treated and released. The two coworkers sustained temporary hearing loss.