Abstract: Employee #1, an on-shift maintenance technician, and Employee #2, a process technician, were trying to cold-start one of several steam-fired utility boilers at the refinery. The boiler had been down for several days to undergo preventive maintenance. They had tried several times to light-off the main burner when the boiler chamber exploded. Employee #1 was killed instantly and Employee #2 sustained injuries when he was struck by flying pieces of debris. Subsequent investigation revealed that 1) the light-off took several attempts due to a high flow of forced draft air; 2) safety systems, such as flame scanners, had been undergoing repairs over the previous month; and 3) equipment intended for maintenance testing was used during light-off. Neither employee had much experience with the equipment, and it was not well documented in the company's product and identification diagrams and operating procedures. In addition, the employer did not manage for the temporary loss of safety systems. The documentation of maintenance testing of the boiler equipment showed a high reliance on the inspections conducted for state certification and insurance purposes.