By: ICN Bureau
Last updated : February 25, 2026 4:57 pm
The investigation found that inadequate procedures and improper pipe identification led to the fatal 27,000-pound release
The U.S. Chemical Safety Board (CSB) released its final report regarding the October 2024 toxic hydrogen sulfide release at the PEMEX Deer Park refinery in Texas, which killed two contract workers. The investigation found that inadequate procedures and improper pipe identification led to the fatal 27,000-pound release.The U.S. Chemical Safety and Hazard Investigation Board (CSB) today released its final investigation report into the fatal October 10, 2024 release of toxic hydrogen sulfide at the PEMEX Deer Park Refinery in Deer Park, Texas.
Two contract workers died as a result of exposure to the toxic gas, 13 others were transported to local medical facilities, and dozens more were treated at the scene. Over 27,000 pounds of toxic hydrogen sulfide gas were released during the incident, and a shelter-in-place order was issued for two neighboring cities.
The release continued for nearly one hour until refinery emergency responders reassembled the leaking flange and stopped the discharge. Although the refinery did not sustain physical structural damage, the company reported approximately $12.3 million in property damage related to loss of use of the Amine Unit and downstream processes.
CSB Chairperson Steve Owens said, “Two people died and the surrounding community was put at risk because of a completely preventable mistake. Companies must ensure that hazards are clearly identified and that effective procedures are in place to protect workers in facilities like this and the people who live and work nearby.”
The CSB’s final report concludes that the incident resulted from the failure to positively identify the correct equipment before mistakenly opening the piping that contained hydrogen sulfide instead of the piping that had been clear of the toxic gas. Contributing to the severity of the incident was the refinery’s failure to adequately assess the hazards of conducting pipe-opening activities in an active unit next to an area where numerous other workers were present. The investigation also found that deviations from established policies and procedures contributed to the event.
The CSB’s final report further identifies several key safety issues:
Positive Equipment Identification: The CSB found that the refinery lacked an effective method to clearly identify the correct piping flange before work began. Drawings and flange lists were insufficient to distinguish nearly identical segments, and the identification tag for the correct flange was placed out of view. Without reliable identification, workers searched for unlocked flange devices similar to what they had seen elsewhere in the refinery. The CSB noted that accidental releases from opening the wrong equipment are common in the chemical and refining industries and that no industry-wide standard currently addresses this issue.
Work Permitting and Hazard Control: The refinery issued a broad work permit covering multiple jobs with varying hazards and without clear hold points. Workers overlooked a written instruction to stop work and obtain an operator’s presence before opening the hydrogen sulfide piping. The permit also failed to address the hazard of opening piping in an operational unit upwind of other contractors.
Turnaround Contractor Management: On the day of the incident, workers were reassigned from a shutdown unit to a partially operational unit containing hydrogen sulfide. This abrupt change, combined with the proximity of the units, led workers to believe they were still working in the shutdown environment, and they were not specifically informed of the risks in the operational unit.
Conduct of Operations: The CSB identified gaps between written procedures and actual practices at the facility. While the refinery’s policies aligned with industry standards, management and operations personnel often misunderstood or deviated from them, contributing to failures in work permitting and hazard evaluation.
CSB Investigator-in-Charge Tyler Nelson said, “Opening hazardous process piping is a common maintenance activity that can be performed safely with effective equipment identification and work permitting practices. This tragic incident underscores the critical importance of equipment identification methods that are clear, consistent, and verified by both facility operators and contract workers before equipment is opened. Strong equipment marking practices, effective work controls, and disciplined operations are essential to preventing deadly releases like this one.”