Abstract: Employees #1 and #2, subcontractors, were assigned to install an orifice flange on a 1 1/2 in. fuel oil return line that extended from a boiler to a storage tank. The line had been charged with #2 fuel oil before the assignment. Upon cutting the line with a Port-A-Band saw, Employee #1, the fitter, had drained residual oil from a portion of the line. Fuel oil remained in other portions of the line. When a 6 in. section of line was removed, the flange was prepared to be installed. Employee #1 held the flange in place while Employee #2, a welder, tacked it on top. When he began the bottom tack, a flash fire engulfed the employees. Employee #1 was burned over 90 percent of his body and died the following day. Employee #2 was burned over 50 percent of his body and died approximately 6 weeks later.