Abstract: Employee #1, a maintenance mechanic, was changing a leaking valve on an ammonia line. Employee #1 failed to follow the proper procedures and inadvertently opened one valve instead of closing it. He then proceeded to loosen the leaking valve without first testing it to make sure the ammonia had been turned off. As Employee #1 turned the valve to remove it, he discovered that the line was wide open and he was sprayed with the ammonia. He was wearing gloves and a canister type gas mask at the time, but the mask fell off during the confusion. Employee #1 was hospitalized for chemical burns. The building was evacuated until repairs were made.