Abstract: On June 13, 2001, Employees #1 through #7 were working near a sodium hypochlorite tank. Employee #1 was operating a tanker truck containing 4000 gallons of ferric chloride. He drove his truck onto the facility and stopped at the administration and control building. After talking with the receptionist, she contacted the supervisor of the facility and asked him to take Employee #1 to the delivery site. However, the supervisor escorted him to the sodium hypochlorite building and pump station, which was near the ferric chloride delivery building. The supervisor told the Employee #1 to hook up to the middle fitting on the side of the sodium hypochlorite building. The middle fitting had a sign with "hypo" written on it hanging from the fitting. Employee #1 asked the supervisor several times about whether this was the correct place to unload the ferric chloride, and he was told it was the correct place. Employee #1 hooked up to the hypo fitting and began unloading the ferric chloride into sodium hypochlorite tank. About 400 gallons of ferric chloride were unloaded before he noticed a cloud forming around the hookup. He ran into the cloud to stop the unloading and then went for help. Chlorine gas had formed from the reaction between ferric chloride and the sodium hypochlorite. Other employee observed the cloud formation and informed the supervisor. The supervisor got his respirator and went to the hypochlorite building to check the situation out. The supervisor put on the respirator, which was a full-face chemical respirator with chlorine cartridges, but donned no other personal protective equipment. However, the respirator was not suitable for the situation; as he got close to the scene, the supervisor smelled something through his mask. He left the area and went to find another employee, who was the chief of operations, to report the problem. The chief of operations responded by donning just a self-contained breathing apparatus and went into the building to check the tanks for leaks. The chief of operations felt the skin on his legs begin to get hot within a short time, so he left the building and went back to the administration building to wait for the hazardous material responders to arrive. Employees and management said the chlorine alarm at the building sounded, but no one knew at what level the alarm was set to go off. Hazmat teams and fire departments arrived at the building and gained control of the situation. Four employees were exposed to the chlorine gas and were experiencing minor health effects. They were transported to the hospital for observation. Two of these employees showered and changed clothes at the plant before they went to the hospital. A fifth employee who had been near the incident site had left the plant after his shift and went to the hospital. At the hospital, all employees exposed to the hazardous vapors were medically evaluated for dermal and inhalation toxicity and treated for the injuries suffered from contact with the chlorine vapors.