A runaway chemical reaction inside a residue treater pressure vessel, which led to over pressurization and explosion of the vessel, resulted from multiple deficiencies during a lengthy startup process at the Bayer CropScience plant in Institute, W.V., says the U.S. Chemical Safety Board in its final report on the incident.

The vessel careened into the methomyl pesticide manufacturing unit, leaving a fireball in its wake. The report also 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 explosion and fire killed two workers and injured eight others.

According to the CSB, 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 pesticides. In its report, the CSB notes that the startup 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 (PHA), as required by regulation.

To review the complete report, visit www.csb.gov.