A “thermal runaway reaction,” likely due to lapses in chemical process safety management, caused last summer's explosion at Bayer CropScience's production facility, U.S. Chemical Safety and Hazard Investigation Board investigators said April 23.

At a public meeting in Institute, W.Va., where the pesticide manufacturing complex is located, CSB investigators presented preliminary findings from their inquiry into the Aug. 28, 2008, blast that killed two workers and caused property damage up to seven miles away.

The explosion, which risked exposing area residents to methyl isocyanate (MIC), was caused when high temperature and pressure ruptured a methomyl residue treater, throwing the 5,000-pound vessel 50 feet into the air. Investigators said the explosion nearly damaged a tank holding about 13,000 pounds of MIC, a raw material used to manufacture the insecticide Larvin™, the chemical that caused death and injury in the Bhopal accident 25 years ago.

Bayer has worked with CSB investigators on the scene, but CSB Chairman John Bresland expressed “disappointment” in the company's efforts to block public presentation of the inquiry's findings by citing security-sensitive information as defined under the Maritime Transportation Security Act and Chemical Facility Anti-Terrorism Standards (12 SNET 63, 4/28/09). This legal challenge has consumed an inordinate amount of board resources and slowed the investigation's progress, according to Bresland.

Although Bayer continues to invoke secrecy claims and has not yet given the board all of the documents it has requested, Bresland said the investigation will be “thorough and complete” and performed with a firm commitment “to the public's right-to-know.”

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