Abstract: A 54 1/2 in. wide by 7 ft high by 13 ft 5 3/8 in. long gas sterilizer vessel was being pressurized with compressed air when it exploded. The vessel was designed and manufactured to operate at 15 psi, whereas the controls and valves were designed to operate at 6 psi. The employer was experiencing a problem with the time cycle and was running a test at the time of the explosion. The vessel was usually pressurized with ethylene oxide gas to 6 psi. For test purposes, they were using compressed air with the regulator set at 60 psi. The controls on the vessel did not function, thereby permitting the vessel to pressurize more than 6 psi. There were no employees in the room when the vessel exploded. The 7 1/4 in. thick by 60 3/4 in. wide by 90 in. long door to the vessel completely separated from it and was blown 22 ft 7 in. , creating large holes in a wood frame partition wall and an 8 in. concrete block wall. The safety relief valve, with 15 psi capacity of 95 cfm (cubic feet per minute), did not open to relieve the pressure. There were no reported injuries.