Abstract: On August 7, 2009, Employees #1 and #2, with LP Electric, Inc. (an electrical contractor), were troubleshooting the electrical system of an air conditioning unit at a retail store. They located the electrical disconnect for the AC unit at the main electrical distribution panel. Using a multi-meter, Employee #2 confirmed this to be the correct disconnect by verifying deenergization at the AC unit, and then returned to electrical panel with Employee #1. Employee #1 opened the panel door by placing the energy isolating device into the off position, replaced a blown fuse, and closed the panel, which reenergized the AC unit. Both employees again approached the AC unit to test the adequacy of the unit's voltage and amperage. After observing correct measurements at the AC unit, both employees returned to the electrical panel. Employee #1 put the energy isolating device in the off position to open the panel and evaluate the fuses. Employee #2 stood to the side holding the panel door open. Employee #1 was immediately in front of the opened panel and noticed that the B-leg fuse was warm to the touch. To check the fuse connection Employee #1 used an uninsulated screwdriver to tighten a lug. When the screwdriver contacted the frame of the electrical panel door, an arc flash occurred. The employees were transported to St. Vincent's hospital. Employee #1 was hospitalized for burns to his face, arms, and hands. Employee #2 was hospitalized for arm burns. Employees were not wearing personal protective equipment. The accident occurred indoors, and weather was not a factor.