Abstract: Employees #1 and #2 were in a 4 ft deep excavation at a construction site, removing, replacing, and resealing the leaking manhole cover from an underground 8,000-gallon gasoline tank. They had removed several bolts and nuts holding the cover in place, but were having difficulty removing the remaining fasteners. Employee #1 used an electric right-angle grinder borrowed from the station owner to remove two of the remaining bolts and nuts. According to Employee #2, Employee #1 had pushed the hot bolts into the tank. As Employee #1 was grinding the third bolt, there was an explosion in the tank. Employee #1 was thrown 228 ft from the top of the tank and was killed. Employee #2 sustained injuries, but did not require hospitalization. They were using a Venturi air blower to remove vapors from the gasoline tank, but Employee #1 was using an electric grinder that was inappropriate for this task and that, according to his coworker, was generating a lot of sparks. The explosion was most likely caused by sparks and/or the hot bolts igniting explosive vapors in the tank.