"In a report scheduled for Board consideration at a public meeting this evening in Institute, the 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 and exploded. The vessel 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. The 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.
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. The 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.
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. For example, operators were troubleshooting several equipment problems and during the startup, inadvertently failed to prefill the residue treater vessel with solvent. A safety interlock was designed to stop workers from introducing highly-reactive methomyl, but it was bypassed as had been done in previous operations with managers’ knowledge. Once the chemical reaction of the highly concentrated methomyl started, it could not be stopped, and the temperature and pressure inside rose rapidly, finally causing an explosion.”
Read the news release in this link.
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. For example, operators were troubleshooting several equipment problems and during the startup, inadvertently failed to prefill the residue treater vessel with solvent. A safety interlock was designed to stop workers from introducing highly-reactive methomyl, but it was bypassed as had been done in previous operations with managers’ knowledge. Once the chemical reaction of the highly concentrated methomyl started, it could not be stopped, and the temperature and pressure inside rose rapidly, finally causing an explosion.”
Read the news release in this link.
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