CSB: Bayer Explosion Caused by Runaway Chemical Reaction

May 6, 2009
A large explosion and fire that took the lives of two workers at the Bayer CropScience plant in August 2008 was caused by a thermal runaway reaction during the production of an insecticide. The event likely resulted from significant lapses in chemical process safety management at the plant, said U.S. Chemical Safety Board (CSB) investigators after their preliminary findings.

The blast on August 28, 2008 in Institute, W.Va., occurred as the runaway reaction created extremely high heat and pressure in a vessel known as a residue treater, which ruptured and flew about 50-feet through the air, demolishing process equipment, twisting steel beams and breaking pipes and conduits. Two operators died as a result.

Eight workers reported symptoms of chemical exposure, including aches and intestinal and respiratory distress. These workers included two employees of the Norfolk Southern railway company, six firefighters.

"The explosion at Bayer was a very serious and tragic event that could have had additional grave consequences,” said CSB Board Chairman John Bresland. “There were significant lapses in the plant's process safety management, including inadequate training on new equipment and the overriding of critical safety systems necessitated by the fact the unit had a heater that could not produce the required temperature for safe operation.”

The Explosion

Bresland explained that the explosion occurred within 80 feet of a pressure vessel containing more than 13,000 pounds of methyl isocyanate, or MIC, a raw material for the pesticide the company was making at the time. This same chemical caused death and injury in the Bhopal accident 25 years ago, he said.

CSB Lead Investigator John Vorderbrueggen noted the accident occurred after an extended maintenance shutdown of the entire Methomyl section of the Larvin pesticide-manufacturing unit. He said Bayer had recently upgraded the computer control system for the unit, resulting in “completely different” control screens, and operators were not yet fully trained on the new system and the operating procedures for the unit were out of date. In addition, he said the residue treater, a large pressure vessel, had an undersized heater.

"As a result of equipment deficiencies, improper procedures and lack of training on brand-new computerized control equipment," Vorderbrueggen said, "the vessel was charged with as much as a 20 percent solution of Methomyl in solvent, whereas the residue treater was designed to safely decompose the chemical at a concentration of less than 1 percent in solution."

CSB reported that operators attempted to check the residue treater vent system as the pressure rose. But the residue treater ruptured, suddenly released 2,500 gallons of Methomyl-solvent liquid and chemical decomposition products."

CSB also is examining operator fatigue as a possible contributor to the accident. Unit operators worked very high overtime levels during the three months prior to the accident, averaging almost 20 hours a week of overtime. Operators repeatedly worked 12-hour days, and sometimes up to 18 hours, with very few days off.

Bayer CropScience in Institute is a large chemical complex of more than 400 acres that was first constructed in the 1940s. Until 1986, it was owned by Union Carbide, which produced carbamate pesticides at the site. It was acquired by Bayer in 2002, and now has more than 500 employees.

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