Abstract: At approximately 2:00 p.m. on August 26, 2004, Employee #1 and several coworkers were installing insulation on 20- to 22-gauge, galvanized sheet metal HVAC ducts on the fifth floor of a building. Each worker was using a ProWeld International CD- 212P capacitor discharge stud welding machine with a magnetic chuck to weld 2 in. long AGM #4 12-gauge cup head pins to the insulation and ducts, which had an aluminum skin. Employee #1 had been working near two ducts when a coworker spotted him lying on a pile of metal conduit in front of the ducts. Several other coworkers approached when they realized that he was unconscious and did not have a pulse. Two coworkers attempted CPR until paramedics arrived, but attempts to revive him were unsuccessful; Employee #1 was declared dead at 3:03 p.m. The 4 ft wide ducts Employee #1 was working near were a foot apart and on top of a concrete pad that extended through the roof of the building. The installation work appeared to be finished on the front, back, and outside of the ducts. The installation inside, between the ducts, was not yet done. Two pieces of insulation were partially attached to the rear corners. The area in front of the duct was 6 ft 5 in. wide and had piles of metal conduit. The welding machine's ground cable, a "C" clamp, was attached to the duct access panel lock. The machine was set for straight polarity and 80 volts. Evidence found during the investigation suggested that the machine arced near the magnetic chuck, shaft, and nut on the "C" clamp, and that Employee #1 was electrocuted. It was also noted that he was not wearing gloves or similar protective equipment.