Abstract: Employees #1 through #4 were working in the vicinity of an oil field storage tank. Earlier, a heater had been removed from the tank and repaired; it was moved to within approximately 18 in. of the tank, but reinstallation was postponed until a smokestack bracket was welded to the top of the tank. Escaping hydrocarbons from the 400-barrel tank were ignited by the welding operation, resulting in an explosion. Employee #1 sustained second- and third-degree burns over 30 percent of his body and was transported to a burn treatment center. Employees #2 and #4 were hospitalized for treatment of second-degree burns and a fractured leg. Employee #3 was treated for burns and released. Although the tank had been washed, no monitoring had been conducted for combustible vapors, hydrogen sulfide, or oxygen.