Abstract: On July 12, 2007, Employee #1 was assigned to report to a business to diagnose and repair electrical problems before it opened for the day. The business was in a three-story building, with the main electrical panel in the basement and sub-panels on the first and second floors. Employee #1 began working on the first floor panel while it was energized. He removed the panel cover, exposing the electrical components, then pulled out three circuit breakers to clean the corroded contact points. As he did this, he saw that the busbar was pitted, which made him think there had been episodes of overheating within the panel. He began scraping the contacts on a circuit breaker with a metal tool when he heard small arcing in the panel. There followed a thermal explosion with a fireball. Employee #1's clothing caught on fire, so he rolled on the floor to extinguish the flames, but the clothes kept burning. He then ran out of the building and again tried to extinguish the fire before he removed his shirt. He sustained first-,second-, and third-degree burns. He was transported by Emergency Services to the UC Davis Medical Center.