Abstract: At approximately 5:00 a.m. on April 13, 1989, Employee #2 accidentally added 5 to 9 gallons of concentrated nitric acid to a 200 gallon tank containing 14 to 16 oz of sodium cyanide at the barrel line. Employee #3, without wearing a respirator or protective clothing, took a detector tube reading over the cyanide tank; the result showed an HCN level greater than 165 mg/m3, which is about three times the IDLH level of 60 mg/m3. The only other employees near the HCN release were Employee #1 and Employees #4 through #11, who were approximately 70 ft away at a break area. They were told to evacuate the plant immediately. None of the eleven employees experienced any ill health affects, but all were told to report to the hospital as a precautionary measure. They were evaluated by a doctor and released from the hospital. Employees wearing full-face air line respirators then proceeded to clean up the area by draining the contents of the tank into four 55 gallon drums. The plant was ventilated; HCN tests were negative; and the employees were permitted back into the plant.