On October 10, 2024, contract workers performing maintenance at the PEMEX Deer Park Refinery in Deer Park, Texas, opened what they believed was the correct pipe flange in the facility’s Amine Unit. It was not. The flange they opened was pressurized with hydrogen sulfide, one of the most acutely toxic gases encountered in petroleum refining. Over 27,000 pounds of H2S poured into the air over the next hour, killing two workers, sending 13 others to area hospitals, and forcing shelter-in-place orders across the neighboring cities of Deer Park and Pasadena.

The U.S. Chemical Safety and Hazard Investigation Board released its final investigation report on February 23, 2026, and the findings paint a picture of cascading safety failures that made a catastrophic outcome all but inevitable. Workers were reassigned from a shut-down unit to a partially operational one without being told about the active hazards. Piping was inadequately labeled. Work permits covered multiple jobs without clear hold points or hazard controls. Written safety procedures existed on paper but were routinely misunderstood or ignored in practice. The CSB concluded that the incident was entirely preventable — and that no industry-wide standard currently addresses the identification of equipment before it is opened for maintenance.

Here is what the CSB investigation found, why hydrogen sulfide remains one of the deadliest hazards in refinery work, and what legal rights are available to workers and families affected by toxic chemical releases at Texas refineries.

Inside the CSB’s Investigation: What Went Wrong at PEMEX Deer Park

Four Critical Safety Failures the CSB Identified

The CSB’s investigation identified four interconnected safety failures that turned a routine maintenance activity into a fatal incident. First, the refinery lacked an effective method to positively identify the correct piping flange before work began. Drawings and flange lists could not distinguish between nearly identical pipe segments, and the identification tag for the correct flange had been placed out of the workers’ line of sight. Without reliable identification, the workers searched for unlocked flange devices similar to what they had seen elsewhere in the refinery and opened the wrong one. The CSB noted that accidental releases from opening the wrong equipment are a recognized and recurring problem across the chemical and refining industries, yet no industry-wide standard currently exists to address positive equipment identification before maintenance work begins.

Second, the work permit issued for the job covered multiple tasks with varying hazard levels and lacked clear hold points. Workers overlooked a written instruction requiring them to stop and obtain an operator’s presence before opening piping that contained hydrogen sulfide. Third, the workers had been abruptly reassigned from a unit that was fully shut down to one that was still partially operational. This transition was not accompanied by a specific briefing about the active hazards in the new work area, and the workers operated under the assumption that they were still in a shut-down environment. Fourth, the CSB found systemic gaps between the refinery’s written safety policies and actual practices on the ground. While PEMEX Deer Park’s written procedures aligned with industry standards, management and operations personnel routinely misunderstood or deviated from them, undermining the entire safety management system.

Why Hydrogen Sulfide Is One of the Deadliest Hazards in Refinery Work

Hydrogen sulfide is the second leading cause of fatal gas inhalation in American workplaces, behind only carbon monoxide. At concentrations above 500 parts per million, H2S causes rapid unconsciousness and death — a phenomenon known in the industry as “knockdown.” The gas is particularly insidious because at high concentrations it overwhelms the olfactory nerve, eliminating a worker’s ability to smell the gas’s characteristic rotten-egg odor. A worker who can no longer detect the smell may assume conditions are safe when in fact the exposure has already reached lethal levels. Bureau of Labor Statistics data show that hydrogen sulfide killed at least 106 workers in the United States between 2001 and 2017, with the majority of those fatalities occurring in confined spaces and in the oil and gas sector. Researchers have noted that the true number is likely higher, as H2S poisoning can be difficult to identify when it leads to secondary events like falls from height.

The PEMEX Deer Park incident illustrates why H2S is so dangerous in refinery environments specifically. The gas was contained in pressurized piping within the Amine Unit, a system designed to remove sulfur compounds from refinery gas streams. When the wrong flange was opened, the release was immediate and catastrophic. The first worker died at the source. The second was working in an entirely different unit downwind and was killed by the drifting vapor cloud. Workers who are not in the immediate vicinity of a release can be fatally exposed simply by being downwind, often with no warning and no time to evacuate. This is why the CSB’s finding that the work permit failed to account for the presence of other contractors working in adjacent areas upwind of the release point is so significant.

Contract Workers Bear the Highest Risk

The two workers killed at PEMEX Deer Park were both employed by contractors, not by the refinery itself. This is consistent with a broader and well-documented pattern in the refining industry. According to CDC data, approximately three-quarters of all oil and gas extraction fatalities between 2014 and 2019 were among contract workers. Contract workers perform the most hazardous maintenance and turnaround activities at refineries, yet they are often less familiar with site-specific hazards, less integrated into the facility’s safety culture, and more vulnerable to the consequences of poor communication and inadequate safety management by the host facility.

The PEMEX Deer Park incident is a case study in how this dynamic can turn deadly. The Repcon workers were reassigned from one unit to another without a proper safety briefing. They were working in an environment they did not fully understand, on equipment they could not reliably identify, under a work permit that failed to address the most critical hazard they faced. The CSB’s investigation makes clear that the responsibility for these failures falls on the refinery operator, not on the workers who were placed in an impossible situation. PEMEX Deer Park has a troubling safety record beyond this incident — the Texas Commission on Environmental Quality has documented 14 air emission events at the facility since 2022, and the Environmental Integrity Project has identified the plant as the worst source of benzene air pollution among U.S. refineries.

Legal Rights for Workers and Families After a Refinery Chemical Release

Workers who are injured by toxic chemical releases at Texas refineries, and the families of those who are killed, have significant legal options that extend well beyond workers’ compensation. Texas is unique among states in that it does not require employers to carry workers’ compensation insurance. Many refinery operators and contractors are “non-subscribers” under the Texas workers’ comp system, which means that injured workers may have the right to file a personal injury lawsuit directly against their employer without the limitations and damage caps that workers’ comp systems impose in other states.

Beyond direct employer liability, workers and families may also have claims against the refinery operator as the premises owner. When a refinery like PEMEX Deer Park controls the worksite, issues the work permits, and manages the overall safety environment, it can be held liable for injuries and deaths caused by its failure to maintain safe conditions — even when the victims are employed by a third-party contractor. The CSB’s findings that PEMEX Deer Park failed to properly label equipment, issued deficient work permits, and failed to inform workers of active hazards all establish the kind of safety failures that support premises liability and negligence claims.

Product liability claims may also be relevant where equipment design or safety device failures contributed to the severity of a release. In cases involving hydrogen sulfide, claims may arise against the manufacturers of detection equipment, alarm systems, or personal protective equipment that failed to function as intended. Additionally, the CSB’s recommendation that ASME develop industry-wide standards for equipment marking before opening acknowledges that the absence of such standards has been a contributing factor in incidents like this one across the industry.

The most important step for any worker or family affected by a refinery chemical release is to act quickly. Evidence at industrial facilities can be altered, repaired, or destroyed within days of an incident. Maintenance records, work permits, safety logs, and atmospheric monitoring data are controlled by the companies involved and may not be preserved unless a legal hold is demanded early. The CSB’s investigation report, OSHA findings, and TCEQ enforcement records can all serve as critical evidence in civil claims, but experienced legal representation is essential to ensure that these materials are identified, preserved, and used effectively.