Abstract: At approximately 10:00 a.m. on June 25, 2002, Employee #1, an electrician, and his coworker-assistant, were installing a new 277/480-volt panel in Building #34B at a biomedical industrial park to provide power for an oven and an air conditioning unit. The job also involved providing lights above the T-bar ceiling. Just prior to the accident, Employee #1 removed a cardboard box that had been placed over an existing Square D bus duct (#CFW253OG2LFUSU46B16; series 1 system 3P4W; FO8905-0104) that was sticking out from the wall inside a building. Based on a request from the electrical inspector, the general contractor asked the electrician to make the 480-volt bus duct safe without having to cover it with a cardboard box. Employee #1 planned to have a plastic cover cut to place over the exposed conductor. He was standing on a fiberglass ladder to remove the cardboard box and his helper, who was at the foot of the ladder, handed him the plastic cover. Employee #1 was holding up the cover to estimate where he would have it cut when the bus duct exploded. He suffered second- and third-degree burns over 40 percent of his body, including his chest and arms. His trachea also sustained burns. It was subsequently determined that the bus duct was energized at the time the box was removed and the plastic cover was being measured. Employee #1 said that he did not think he had touched the bus duct. He also said that he did not feel it was necessary to de-energized the bus duct because he was just measuring it, and that he planned to lock-out and tag-out the unit before he attached the plastic cover. The area between the conductors indicated high levels of heat due to the melted metal and the conductors themselves being damaged. Inspection of the bus duct suggested that something touched the ground at the end of it, and that the contact was for an extended period rather than being instantaneous.