Abstract: Employees became aware of an ammonia smell or were told by others that there was an ammonia leak. They had been instructed to leave the building when such leaks occurred, unless it was a small leak. The employees exited the building through the pump room door to the dock area. The ammonia release occurred due to a stuck pressure relief valve on the system that vented an unknown quantity of ammonia to the outside through a pipe almost directly over the pump room exit door. Employees #1 and #2, the first employees to exit, inhaled a concentrated amount of ammonia as they went through the gas cloud. They suffered dizziness, weakness, eye irritation, stomach pain, and difficulty breathing. They were treated at the hospital emergency room and released. They were instructed to take a couple of days off from work. The other employees, warned by Employees #1 and #2's reaction, evidently held their breath and were not affected.