In its final report on the Aug. 28, 2008, Bayer CropScience pesticide manufacturing unit explosion that killed two workers and injured eight others, the U.S. Chemical Safety Board (CSB) found multiple deficiencies during a lengthy startup process that resulted in a runaway chemical reaction inside a residue treater pressure vessel.
The vessel ultimately over pressurized, exploded and careened into the methomyl pesticide manufacturing unit, leaving a huge fireball in its wake. The report found that had the trajectory of the exploding vessel taken it in a different direction, pieces of it could have impinged upon and possibly caused a release from piping at the top of a tank of highly toxic methyl isocyanate (MIC).
The accident occurred during the startup of the methomyl unit, following a lengthy period of maintenance. CSB found the startup was begun prematurely, a result of pressures to resume production of the pesticides methomyl and Larvin, and took place before valve lineups, equipment checkouts, a pre-startup safety review and computer calibration were complete. CSB investigators also found the company failed to perform a thorough Process Hazard Analysis, or PHA, as required by regulation.
This resulted in numerous critical omissions, including an overly complex Standard Operating Procedure (SOP) that was not reviewed and approved, incomplete operator training on a new computer control system and inadequate control of process safeguards. A principal cause of the accident, the report states, was the intentional overriding of an interlock system that was designed to prevent adding methomyl process residue into the residue treater vessel before filling the vessel with clean solvent and heating it to the minimum safe operating temperature.
Furthermore, the investigation found that critical operating equipment and instruments were not installed before the restart and were discovered to be missing after the startup began. Bayer's Methomyl-Larvin unit MIC gas monitoring system was not in service as the startup ensued, yet Bayer emergency personnel presumed it was functioning and claimed no MIC was released during the incident.
"The deaths of the workers as a result of this accident were all the more tragic because it could have been prevented had Bayer CropScience provided adequate training and required a comprehensive pre-startup equipment checkout and strict conformance with appropriate startup procedures," said CSB Chairperson Dr. Rafael Moure-Eraso. "This would have revealed multiple dangerous conditions and procedures that were occurring at a time when the company wanted to restart production of a key pesticide product. Startups are always a potentially hazardous operation, but to begin with computer control systems that have not been checked, while bypassing safety interlocks, is unacceptable."
The investigation report makes recommendations to the company and its Institute plant and to OSHA, EPA and several West Virginia agencies. Citing a highly successful county program to ensure refinery and chemical plant safety in Contra Costa County, Calif., the CSB report recommends the West Virginia Department of Health and Human Resources establish a "Hazardous Chemical Release Prevention Program" that would have the authority to inspect and regulate such plants and make public its ongoing findings.
CSB Investigations Manager John Vorderbrueggen noted that a major contributing factor to the accident was a series of equipment malfunctions that continually distracted operators.
"Human factors played a big part in this accident, and the absence of enforced, workable standard operating procedures and adequate safety systems meant that mistakes could prove fatal," he said.
The investigation also examined the potential consequences of a hypothetical trajectory of the careening residue treater vessel that would result in its hitting the heavy steel mesh ballistic shield surrounding the above-ground MIC tank. Had the residue treater struck the shield structure near the top of the frame, the displaced frame could have contacted an MIC pipe, which might have resulted in an MIC release into the atmosphere. Moure-Eraso stressed that "any significant MIC release into the atmosphere along the Kanawha Valley could have proven deadly."
According to Moure-Eraso, Bayer announced last year that it would no longer store MIC above ground. The company also announced that in approximately 18 months, it will end MIC production and use at the Institute facility, which is the only place in the country still storing large quantities of MIC.
"Bayer's decision to end pesticide production using MIC was, I understand, done for its own business reasons. But for whatever reasons, the eventual elimination of this chemical will enhance safety in the Kanawha Valley, for workers and residents alike, and is a positive development in my view," Moure-Eraso said.