Investigation: Feds cite safety lapses, mechanical failures in fatal DuPont accident in Texas

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), which investigates 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 in preliminary findings.

On the basis of its internal review, DuPont says 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.”

According to CSB, the leak occurred after an unplanned shutdown of the methomyl production unit. 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.