Abstract: On Monday evening, January 10, 1994, an ethylene oxide leak occurred on the P-1 level of Century City Hospital in the Central Services Area. This occurred after Employee #3 (engineering staff) changed the ethylene oxide tank. Investigation showed that Employee #3 did not close the bleedoff valve during the tank change. The leak continued undetected for about 20 minutes, until Employee #1 (Central Services Employee) saw the visual alarm on the ethylene oxide monitoring equipment and told Employee #2 (Central Services Employee) to evacuate the area. Employee #2 went to the tank area and closed the bleedoff valve.