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DuPont Safety Lapses, Mechanical Failures Cited In Fatal Texas Accident

Investigation: Chemical Safety Board links methyl mercaptan leak to process vents at firm’s La Porte facility

by Glenn Hess
December 16, 2014

Mechanical problems and ineffective safety practices were likely factors in the chemical leak that killed four workers last month at DuPont’s complex in La Porte, Texas, federal authorities say.

The U. S. Chemical Safety & Hazard Investigation Board (CSB), an independent agency charged with investigating chemical accidents, points to problems with the vent system in the building where the release of 23,000 lb of toxic methyl mercaptan originated on Nov. 15.

In addition, DuPont “did not effectively implement good safety practices” that require workers to wear air respirators and other protective equipment, CSB alleges.

On the basis of its own review, DuPont says it believes that CSB’s description of the circumstances “leading to the release of methyl mercaptan from the vent header system is the most likely scenario.” But the company adds that it “does not necessarily agree with other aspects of CSB’s statement.”

CSB disclosed preliminary findings from its ongoing inquiry in testimony submitted to two Senate committees on Dec. 11. The panels are examining the Obama Administration’s efforts to improve safety at chemical facilities.

According to CSB, the leak occurred after an unplanned shutdown of the methomyl production unit because of water dilution in a chemical storage tank. Methomyl is the active ingredient in DuPont’s Lannate brand insecticide.

The agency found that workers were unable to restart the unit because supply piping from a methyl mercaptan storage tank was plugged. “It is likely that methyl mercaptan inadvertently entered the interconnected process vent system inside the building,” CSB says. The release occurred through a valve that was opened as part of a routine effort to drain liquid from the vent system to relieve pressure.

“We found that this vent system had a history of periodic issues with unwanted liquid buildup, and the valve in question was typically drained directly into the work area inside the building rather than into a closed system,” CSB says.

Besides its use in pesticide production, methyl mercaptan, is sometimes used to odorize natural gas. It can cause headaches, nausea, and death, especially when exposure occurs in poorly ventilated, enclosed areas.



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