Abstract: An aluminum billet homogenizing furnace had been operating erratically for several days and would shut itself down. One evening the furnace shut down and Employee #1, a homogenizing handle, relit the furnace. Several minutes later, while he was in front of the furnace, it exploded. As a result of the explosion, the furnace door was blown free from its restraints. Employee #1 was struck and killed by the 3,860 lb door, which landed on top of him. The investigation revealed that the furnace fuel gas to burner #3 was adjusted rich, and that the burner went out. When this occurred, the flame sensor, which was oriented along the axis of the pilot light, still detected the flame from the burner pilot light and did not automatically shut the furnace burner system down. As a result, unburned fuel gas accumulated inside the furnace until it was ignited by one, or all, of the other three burners.