21 April 2009 18:02 [Source: ICIS news]
HOUSTON (ICIS news)--A series of process safety management deficiencies by workers at a Bayer CropScience plant near Charleston, West Virginia, led to the explosion that killed two workers last August, US Chemical Safety Board (CSB) chairman John Bresland said on Tuesday.
Testifying to a US House committee investigating the accident, Bresland said the CSB found the explosion occurred during the restarting of the plant’s methomyl unit after a long maintenance shutdown.
Bresland said a new computer control system was installed at the plant, but workers were not adequately trained on it prior to the startup.
Moreover, an undersized heating system for the residue treater vessel, long-known to Bayer management, required operations to deviate from written procedures, he said.
This required operators to bypass critical safety interlocks intended to prevent the flow of methomyl into the residue treater until the required minimum temperature was reached, Bresland said.
“Our investigation has revealed significant lapses in process safety management that likely contributed to causing this accident,” Bresland told the committee.
“The practice of bypassing the safety interlocks was longstanding and was known to Bayer managers and engineers. But bypassing the safety interlocks made it much more likely to overcharge the vessel with methomyl, which could lead to a catastrophic runaway reaction.”
Additionally, CSB investigators determined that Bayer operators had not pre-filled the treater vessel with heated solvent, as required by the startup procedure. Bresland said the CSB had not determined the reason for that, but said operators had been working shifts of 12 hours or more up to seven days a week.
“As the startup proceeded, concentrated methomyl continued to be pumped into the treater. It eventually overheated and violently decomposed, destroying the residue treater tank.”
From there, the residue treater could have been propelled in any direction, Bresland said. Of significant concern was a large tank that held about 40,000 lb of the toxic petrochemical methyl isocyanate, located about 80 feet from the treater’s original location.
The CSB was set to host its own hearing on Thursday, in which investigators were expected to examine the causes of the accident, the adequacy of the response, and the scope of information provided to first responders, employees and the public, according to CSB spokesman Daniel Horowitz.
The CSB does not issue citations or fines for such incidents but makes safety recommendations to regulatory agencies.
Bayer has not responded to requests for comment from ICIS news.
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