Abstract: At approximately 10:48 a.m. on September 16, 2006, two employees of a utility company, Employee #1 and a coworker, were performing maintenance work (i.e., a clearing procedure) on a 12 kilovolt (kV) vacuum circuit breaker (Square D, Type FVR, 12 kV, identified as Circuit Breaker Number 5). Three load disconnect switches and three line disconnect switches were used to isolate the circuit breaker from all sources of potential energy. The disconnect switches were underhung-mounted type (Southern States, 14.4 kV, 3500 Amp, 80 kiloamp "MOM Rating"). Each disconnect switch had two blades, and each blade had a hookstick eye (pull ring), where the blades were opened and closed, one at a time. Employee #1 and his coworker opened the load and the line switch disconnects and connected a laptop computer to the breaker. The coworker walked to the control room to "shoot the breaker" (i.e., conduct Response Time Recording), while Employee #1 stood by the circuit breaker and the laptop. After the coworker shot the circuit breaker, he walked to his truck to obtain some paperwork, and that is when the circuit breaker exploded. Employee #1 sustained serious injuries to his face, neck and right arm, as a result of the electrical blast. Employee #1 was transported to Arrowhead Regional Medical Center, where he was hospitalized for two days, and was then transferred to Grossman Burn Center at 7:20 a.m. on September 18, 2006. Shortly after the blast, it was discovered that one of the blades on the "B" phase of the line side was inadvertently left in the "closed" position, rendering the line side of the circuit breaker energized. It was further discovered that the high-voltage cover on the circuit breaker was removed and that the personal grounds were connected to the station ground grid but not to the circuit breaker.