The U.S. Chemical Safety and Hazard Investigation Board (CSB) released a second update on its ongoing investigation into the fatal hydrogen sulfide release that occurred on October 10, 2024, at the PEMEX Deer Park Refinery in Deer Park, Texas. Two contract workers died during the incident, and over 27,000 pounds of toxic hydrogen sulfide gas were released. Local authorities issued shelter-in-place orders lasting several hours for the neighboring cities of Deer Park and Pasadena.

The PEMEX Deer Park Refinery is an indirect subsidiary of Pemex, a petroleum company wholly owned by the Federal Government of Mexico. The refinery employs approximately 1,000 personnel and 1,200 contractors. The facility is a petroleum refinery, which produces hydrogen sulfide as a byproduct that can cause serious health hazards if released into the environment.

On the day of the incident, maintenance contractors were working to removing piping isolation devices, called blinds, from ARU6, one of the refinery’s Amine Regeneration Units (ARUs). During the task, workers inadvertently opened a flange on a piping segment of another unit, ARU7, which was still pressurized with hydrogen sulfide gas.

At approximately 4:23 p.m., the ARU7 piping flange was opened, releasing a toxic concentration of hydrogen sulfide gas into the air. One of the contract workers performing the task was fatally injured at the scene. The wind carried the toxic hydrogen sulfide to a nearby unit where other contractors were working. One contract worker downwind from the release also was fatally injured from hydrogen sulfide poisoning.

The CSB’s investigation is ongoing and will focus on the following key areas:

• Safe work factors
• Maintenance Policies and Procedures
• Emergency Preparedness

The CSB’s final investigation report will include comprehensive findings, analyses, and, if applicable, recommendations for improved safety practices to prevent future incidents.

The CSB is an independent federal agency charged with investigating incidents and hazards that result, or may result, in the catastrophic release of extremely hazardous substances.

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Texas