A federal agency looking into the exact causes of a toxic chemical leak at a DuPont plant in Texas that killed four workers says its investigation uncovered flawed safety procedures, design problems and inadequate planning.
On Nov. 15, 2014, a series of events at DuPont‘s La Porte, TX, insecticide plant led to liquid methyl mercaptan draining into a room, creating a toxic gas cloud.
Two workers were killed while in the process of trying to drain liquid from two valves. Two more workers died responding to a distress call one of the other two workers made before succumbing to the toxic gas.
The U.S. Chemical Safety Board released its preliminary findings into the incident.
A chain of events led to the methyl mercaptan release, according to the CSB:
- During delivery of a raw material by tank truck on Nov. 10, 2014, a water dilution system was inadvertently activated and the raw material’s storage tank overflowed, resulting in the shutdown of the insecticide unit.
- When operators attempted a restart on Nov. 12, material blocked a reaction system.
- While trying to clear the blockage, two thousand pounds of water were inadvertently sent to a storage tank containing methyl mercaptan, creating a solid, ice-like hydrate in piping.
- A Nov. 14, a troubleshooter team of managers and engineers developed a plan to apply hot water under the pipes’ insulation to break up the hydrate. Two valves were opened to give the methyl mercaptan a place where it could expand. But the plan didn’t undergo a safety review, and there were no written procedures to guide the plan.
- As methyl mercaptan began to flow in the piping, high pressure alarms for process equipment registered on computer consoles.
- Two workers went to drain pipes, and liquid methyl mercaptan escaped into the building. It quickly began to vaporize, filling the room with a highly toxic gas.
The two workers who responded to the distress call and subsequently died were brothers.
CSB has made recommendations to DuPont for actions to take before restarting the plant. Among the main recommendations:
- Perform inherently safer design review
- Complete more robust process hazard analysis, and
- Assure active workforce participation in the process.
La Porte plant manager James O’Connor said DuPont is addressing the CSB recommendations.
In a statement, DuPont said while it disagrees with aspects of the CSB’s report, the company is coordinating with the agency to implement these action steps:
- improve process hazard analyses
- perform engineering analysis of the building and exhaust ventilation system
- make equipment modifications and redesign, including relief systems, detectors and alarms, and
- develop improved operating procedures and training for all personnel.
OSHA fined DuPont $99,000 and placed it in the Severe Violator Enforcement Program.