Abstract: Employee #1 was patching two pin holes in the burner tube flange on a main crude oil storage tank, which was part of a natural gas pumping unit. Fluid level in the tank was approximately 6 in. above tank floor level. The two pin holes were located at the 7 o'clock position and the 2 o'clock position, which put one hole above the fluid level at the beginning of the flammable range of the crude oil and natural gas in the tank. Employee #1 was welding using a standard Lincoln arc welding unit and Employee #2, a welder's helper, was assisting Employee #1. (Employee #2 was a welder of less experience than Employee #1, who was classified as a senior welder.) The crude oil gases inside the storage tank ignited. Employee #1 died in the explosion. Employee #2 and Employee #3, a production foreman on site to check progress and to set up the next project for this crew, sustained burns due primarily to the flaming crude oil that engulfed them. Employee #2 also sustained major broken bones in the explosion. All three employees had been trained in what the company considered appropriate safety policies.