Abstract: At approximately 10:00 a.m. on September 28, 1999, Employee #1 was in the process of draining refrigeration fluids from the chiller in one of two refrigeration units at the site. Employee #1's supervisor was 200 ft away in the "engineering room". The drain valve on the chiller unit was frozen in the "open" position resulting in the release of residual liquid when Employee #1 removed the 0.75-in. plug from a 0.75-in. ammonia gate valve. Employee #1 managed to radio for help and the supervisor donned an SCBA and escorted Employee #1 to a secure area and administered first aid until medical assistance arrived. Employee #1 was not wearing proper respiratory protection or eye and face protection. The accident occurred because of poor maintenance practices on anhydrous ammonia systems, the lack of proper respiratory, eye and face protection when working with high hazard materials. Employee #1 was hospitalized for several days for treatment of anhydrous ammonia inhalation and burns to the eyes.