The U.S. Chemical Safety and Hazard Investigation Board (CSB) concluded that a lack of a consistent, standardized method to identify idled equipment at Pemex’s Deer Park refinery in Texas was a central factor in a toxic gas release that killed two workers, according to a report released on Feb. 23.
The CSB report states that on October 10, 2024, workers were preparing an idled, de-inventoried unit for upcoming work when one of them opened a flange on a pipe belonging to a nearby operating unit. That action released approximately 27,000 pounds of hydrogen sulfide into the atmosphere, the board said.
One worker who opened the flange died at the scene. As the gas traveled downwind, it incapacitated another worker who was unable to escape and who also died, the report said. Hydrogen sulfide concentrations during the release reached at least 500 parts per million at the Deer Park refinery, the CSB reported.
Thirteen additional workers were taken to medical facilities for evaluation in the aftermath, and local authorities in the Houston suburbs of Pasadena and Deer Park issued shelter-in-place orders while the release progressed.
"The CSB concludes that PEMEX Deer Park had written procedures that standardize pipe marking for pipe cutting but did not have a standardized process for flange opening and blind removal activities," the board wrote. "Had PEMEX Deer Park required clear standardized markings for all line opening activities, this incident may have been prevented."
The report notes that, since the release, the Pemex refinery has implemented a system to identify equipment slated to be opened for work. A Pemex spokesperson was not immediately available to comment on the report, the CSB said.
The CSB’s findings center on procedural gaps for line-opening activities rather than on other causes. The board emphasized a disparity between the refinery’s existing pipe-marking rules for cutting and the absence of an explicit, standardized practice for flange opening and blind removal work.
The sequence of events described in the report is limited to the actions on October 10, 2024 and the immediate consequences documented by the CSB: the large-volume release of hydrogen sulfide, two fatalities, medical evaluations for other workers, local shelter-in-place orders, and subsequent adoption by the refinery of an identification system for equipment to be opened for work.