Abstract: At approximately 8:00 a.m., on July 13, 1999, Employee #1, mixed the chemicals DCPD and Malefic Anhydride in a 6,500-gallon pressure vessel reactor. The coils that loop around the vessel will fill with hot oil of 450F. The reaction had just become exothermic (build up of pressure and heat) when the power went out. The other employees used a UPS 24Volt battery to back up the generator as a source of power and added nitrogen to the 6,500-gallon tank reactor in an attempt to cool it down. A coworker decided to remove the hot oil and add city water to further cool it down. The back up battery lasted 3.5 hours and the power failed again blanking out all computer systems that open and close the valves for the inflow and the outflow of the chemicals. The reactor could no longer be controlled automatically and the valves then defaulted to a fail-safe position. The pressure in the tank began to build due to the addition of nitrogen, and the disk that was rated for 42 psi was now holding 100-psi pressure, causing the disk to blow. A cloud containing DCPD vapors was released into the atmosphere, exposing the employees and employees of other companies in the surrounding areas. Thirty-two employees were hospitalized with symptoms of nausea, headaches, and respiratory problems related to the exposure.