Abstract: An employee worked for a company that installed, maintained, and repaired underground storage tanks and pump equipment for service stations. He was drilling through metal and concrete to install a ring in a manway collar. Flammable vapors filled the space above the gasoline tank where he was working. Apparently, electric arcing from the electric drill, or sparks from the drill bit, ignited the vapors and caused an explosion. The employee sustained burns to his face, wrists, and thighs. He was hospitalized for his injuries for approximately 2 week. No monitoring equipment or ventilation had been used during the repair operation.