Abstract: At 7:45 a.m. on May 31, 1994, a tanker truck delivered sodium hypochlorite to a plant. Approximately 20 gallons were placed in a tank containing 200 gallons of ferric chloride. A reaction occurred that released chlorine gas outside the plant's main building. Employees #1 through #7 experienced short-term overexposure. All were sent to Johnson Memorial Hospital. Employees #1 and #2 were kept 48 hours for observation. The driver had been told three times that the connection was ferric chloride. The hypochlorite fill was 1,000 ft away from the ferric chloride fill. The plant did not verify that the truck was delivering sodium hypochlorite; a ferric chloride delivery was expected the same day. The plant had been using sodium hypochlorite for approximately one month. There were no written procedures for deliveries. Violations of 1910-120, 134, 1200 were found.