But 2,000 pounds of toxic methyl chloride was released before the leak was stopped five days later. An alarm system on the rupture disc was so unreliable that it went off routinely, leading workers to ignore the leak warnings. The problem had come up before, but DuPont had never fixed it, CSB investigators found.
In the oleum incident, corrosion under the insulation caused a leak. DuPont officials knew this could be a problem on the piping in question, but did not include that part of the plant in an improved preventative maintenance plan, according to the CSB.
Board experts blamed the fatal phosgene leak on a worn-out Teflon and braided-steel hose. The hose had been in service for more than seven months, but was supposed to be replaced after 30 to 60 days. The hose ruptured and sprayed Fish in the face with liquid phosgene while he was checking the chemical level in a one-ton phosgene cylinder.
"DuPont did not follow its own standards for the change out of phosgene transfer hoses," the board's report concluded.
DuPont officials also ignored their own experts' concerns that the type of hose used was not safe for a material as toxic as phosgene, and never followed through on recommendations for reconstructing the entire phosgene area of the plant to make it safer, the CSB found.
CSB investigators uncovered internal DuPont documents that detailed the company's consideration in 1988 of the proposal to totally enclose the phosgene area. A company study determined the proposal would be safer, and was affordable at a cost of $2 million.
But the plan was dropped after one employee -- whose name was not made public -- questioned whether the project "sets a precedent for all highly toxic material activities."
Company experts have recommended similar enclosures several times since that 1988 memo, but such projects have repeatedly been delayed, the CSB reported.
In their report, board investigators said, "an enclosure, scrubber system, and routine requirement for protective breathing equipment before personnel entered the enclosure would have prevented any personnel exposures or injuries."
While highly toxic, phosgene is a valuable building block for making other chemicals. At Belle, DuPont was buying one-ton cylinders of phosgene and using the chemical to make intermediates, which were then used to make crop-protection products.
The DuPont phosgene unit has been out of operation for business reasons since the January 2010 incident, and CSB officials urged the company not to restart it unless they build the enclosure.
Belle plant manager Jim O'Connor said DuPont has no plans to resume using phosgene at the plant.
Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.