Abstract: On March 21, 2001, 425 pounds of anhydrous ammonia was released at a printed circuit board manufacturing facility. The anhydrous ammonia release was caused by an over-pressurization of the tank when the heating unit failed to shutdown. The heating unit is used to vaporize the liquid ammonia into a gas. On the day of the accident, a total of 23 employees were exposed to anhydrous ammonia. Employees #1, #2, #3, and #3 were treated for burns, but were not hospitalized for their injuries. Employee #5 and #6 were treated for chemical burns, but were not hospitalized. The remaining 17 employees were taken to the hospital for observation only and were released that same day. All of these employees received exposure to ammonia during the evacuation of the buildings. None of the employees were working near or at the ammonia tank and no employees participated in Emergency Response.