Abstract: On November 3, 1998, Employee #1 was working as part of a three-worker crew conducting boroscope readings inside a tube heat exchanger at a geothermal energy plant. The boroscope utilized a high-temperature halogen light source and was plugged into a 120-volt extension cord. A second work crew removed a valve from a vessel containing isopentane vapor, approximately 8 feet away from the boroscope. In approximately 7 seconds, the vapor cloud released from the vessel was ignited by either the boroscope, extension cord, or other related equipment. Employee #1, who was reading the meter for the boroscope in a slightly sunken area of the ground surface, was caught in the vapor cloud and burned. Written procedures of the geothermal energy plant, which required a hot work permit for any electrically-operated equipment, were not followed. Also, none of the workers involved in the incident were wearing fire-protective clothing. Employee #1 was hospitalized, suffering from second- and third-degree burns on both of his arms.