Abstract: At approximately 4:50 a.m. on April 6, 1994, an automatic control valve operating on an oxygen letdown station at a liquid air handling plant appeared to become inoperative. It was a Masoneilan 3 inch split body globe valve with a domotor actuator and was operating at about 700 pounds of pressure. The plant manager decided that he and two operators, Employees #1 through #3, could throttle the flow at the letdown station by closing the manual block valve. They had closed the manual block valve about two rounds when the automatic control valve unexpectedly slammed shut. This forceful closing was followed by a fire/explosion. The intense reaction of pure oxygen at 700 pounds of pressure consumed/vaporized all material in its vicinity, including the schedule 80 piping system. The three employees received severe burns over most of their bodies. Employee #1 died, and complete recovery of Employees #2 and #3 may not be possible.