Abstract: A circuit breaker supplying an air conditioner on a roof had been opening for several days. Two heating, ventilation, and air conditioning employees were assigned to repair the problem, though neither of them was an electrician. They did not deenergize and lockout the circuit, and they were not wearing any personal protective equipment. The 480-volt circuit breaker was fed by a loop directly from a 13.2-kilovolt transformer. One of the two employees approached the circuit breaker panelboard, which had its cover and door removed some days before the accident. He either reset the faulty breaker or started to remove it, and an electrical fault occurred. Heat from the fault current melted the insulation on conductors at the block connection at the switchgear, causing another fault at this location. As a result of an electric arc from the primary fault, the employee near the circuit breaker sustained burns over 87 percent of his body. He was hospitalized for his injuries. As a result of an electric arc from the secondary fault, the other employee sustained burns over 50 percent of his body. He died from his injuries.