Abstract: The reaction purification and oxidation unit, which produces titanium dioxide, was in normal operation when the oxygen preheater coil failed releasing chlorine, titanium dioxide, oxygen, and insulation (non-asbestos) through the stack into the atmosphere. The released material was carried by prevailing winds over the plants adjacent unit. Operations at the unit were shut down and plant emergency response was activated. Later investigation revealed failure of a control thermocouple, which resulted in the increase of the coil temperature causing loss of vessel containment. Employees #1 and #2 were onsite at their regular assigned duties. Employees #3 and #4 were contract employees. All were exposed to the released materials. Medical attention was given on site at the medical department. All were treated and released back to regularly assigned duties that day.