(193f) Synthron Runaway Reaction and Vapor Cloud Explosion

The CSB investigated a runaway chemical reaction and subsequent vapor cloud explosion and fire that killed one worker and injured 14 (two seriously) at the Synthron, LLC facility in Morganton, North Carolina, on January 31, 2006. The explosion destroyed the facility and damaged structures in the nearby community.

Synthron manufactured acrylic polymers for use as paint and coating additives. The polymers were typically produced inside a batch reactor by chemically reacting a blend of acrylic monomers in a mixture of flammable solvents (?solution acrylics?). The polymerization reaction produced significant heat, which was removed by condensing the solvent vapor in an overhead, water-cooled condenser.

The accident occurred when plant managers increased the batch size for an additive by 12% and front-loaded all of the additional monomer into the initial batch-mode step in the production process. Subsequent laboratory testing by the CSB showed that increasing the batch size in this manner more than doubled the maximum heat output from the reaction. The heat output exceeded the cooling capacity of the reactor's heavily fouled condenser, leading to a runaway reaction. Faulty bolting practices created a weak point in the pressure envelope, leading to a discharge of flammable solvent vapors into the manufacturing building. The resulting vapor cloud exploded.

The CSB identified numerous factors contributing to the incident, including an inexperienced staff, poor training, a lack of hazard awareness, poor oversight by the multinational parent company, and a lack of engineering safeguards and controls. Lessons learned are described.