CSB investigators reported that the waste tank contained about 2,500 gallons of chemicals, including Methomyl, when it exploded. Chemical pipes and venting systems in the unit were also broken open, and their contents released, the CSB said.
"Methomyl is toxic, and its uncontrolled decomposition may release highly toxic byproducts," Bresland told a House subcommittee. "According to publicly available material safety data sheets for Methomyl, those decomposition products may include highly toxic chemicals such as methyl isocyanate, hydrogen cyanide, acetonitrile, carbon monoxide, dimethyl disulfide, nitrogen and sulfur oxides, and methyl thiocyanate."
In prepared testimony for the congressional hearing, Bayer CropScience CEO William Buckner said the company's incident commander that night "continually monitored the air around the facility and detected no potentially harmful chemical emissions that might threaten the community."
"Ultimately, these and other important safety measures in place to protect the MIC day storage tank and its related piping functioned as intended."
And prior to the hearing, in a Feb. 20 letter to the CSB, Bayer lawyer Robert Gombar told government investigators that MIC monitoring results inside the Methomyl unit "are not recorded, but the detection of MIC in the Unit does result in an alarm in the control room.
"Based on all of the information available to [Bayer] at this time, there were no MIC detection alarms during or after the incident on August 28, 2008."
Later, in mid-April, Wey told the congressional investigators that the MIC monitors inside the Methomyl unit were not functioning the night of the explosion.
"We have come to understand that the MIC analyzer array, for want of a better term, the series of analyzers to monitor MIC in the Larvin unit, that device that measures that concentration, was out of service for maintenance repair," Wey told investigators.
Congressional investigators reported that Wey "was unable" to explain why the MIC monitors were out of service on the night of the explosion.
Last week, Wey told the Sunday Gazette-Mail that for some period of time before the explosion -- he couldn't immediately explain how long -- the company was "getting some spuriously high readings" on the MIC monitors. Company officials believed these were "false high readings," and not real indications of MIC in the air, Wey said.
The monitoring system in question consisted of a series of sampling points and a central analyzer unit. The sampling points are located around the Methomyl unit, including the area where the waste tank that exploded was located and across the plant road, where the MIC day tank stands.
Wey explained that Bayer talked to the manufacturer of the monitoring system about the problem.
"Their recommendation to us was to send it back to them to be realigned," Wey said. "I think we were in the process of making arrangements to take it back to them."
But Bayer officials said they felt comfortable starting the Methomyl unit anyway, despite the problems with the MIC monitors.
At the time, Bayer was restarting the Methomyl unit after a long maintenance shutdown, officials have said. Earlier in August, Bayer had announced it was hiring 24 workers in the Larvin unit, as part of a plan to take advantage of increased global demand. Bayer uses Methomyl, which is itself a pesticide, to make Bayer's Larvin insecticide.
Crosby said last week that there was no reason not to restart the Methomyl unit without the MIC monitors.
The monitors, he said, are a "second-level" safety system intended to warn of any leaks, not a primary system -- such as temperature or pressure monitors on the MIC tank -- intended to prevent releases.
"It's not a critical instrument," Crosby said.
Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.