Safety board investigators blamed the explosion on a "runaway reaction" in a 4,000-gallon tank called the "residue treater," which was used to break down methomyl into wastes that are burned in the plant powerhouse.
In their new report, board investigators said plant operators were pressured to restart the unit after a long maintenance shutdown, despite the fact that new operating instructions had not been completed, pre-startup reviews were not performed and equipment examinations not finished.
Employees were not properly trained on an entirely different computer control system, and were working large amounts of overtime under a new management structure that left shift workers without proper supervisors on site at all times.
"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 Moure-Eraso.
In the residue treater, other materials were to be heated to a certain temperature and then a tiny amount of methomyl added for decomposition. Bayer was aware that adding too much methomyl would speed up the reaction to the point of generating heat and pressures that would spiral out of control.
But CSB investigators believe the residue treater had a heater that was too small, and therefore would not bring the unit to a high enough temperature or took too long to reach that temperature. As a result, workers regularly used -- with management's knowledge -- a workaround that deactivated at least two safety controls that prohibited the methomyl from entering the residue treater before the unit was hot enough.
"Once the chemical reaction of the highly concentrated methomyl started, it could not be stopped," Vorderbrueggen said, "and the temperature and pressure inside rose rapidly, finally causing an explosion."
Investigators warned that the explosion sent the residue treater flying across the plant, and that the vessel could have hit an MIC tank located about 75 feet away. The tank was surrounded by a steel "blast blanket," but the CSB found that the equipment provided only "marginal" protection and might not have stopped the tank from being damaged and causing an MIC release.
Board members noted that Bayer has recently announced that it will stop making, using and storing MIC as part of a corporate restructuring, and said the elimination of the chemical inventory is a positive step for the Valley.
"Any significant MIC release into the atmosphere along the Kanawha Valley could have proven deadly, and that concern has been legitimately expressed for decades in the community," Moure-Eraso said. "Bayer's decision to end pesticide production using MIC was, I understand, done for its own business reasons. But for whatever reason, 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."
Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.