CSB Report Describes Cause of 2024 Fatal Hydrogen Sulfide Gas Release
The release of more than 27,000 pounds of hydrogen sulfide gas at a refinery in Texas that resulted in the deaths of two contract workers in October 2024 was the result of “a completely preventable mistake,” says Steve Owens, chair of the Chemical Safety and Hazard Investigation Board. Owens’ remarks were released with CSB’s final investigation report into the incident, which occurred at the PEMEX Deer Park Refinery in Deer Park, Texas. According to the agency, the release was caused by the opening of incorrect equipment during maintenance activities. Contract workers mistakenly opened a flange on piping containing pressurized hydrogen sulfide instead of the flange they were supposed to open, which was approximately five feet away and clear of toxic gas.
“PEMEX Deer Park did not establish an effective method to clearly identify the correct equipment to open before authorizing opening the equipment,” CSB’s report states. “Due to the lack of a reliable method to identify the intended equipment, the [contract] workers searched for unlocked flange-locking devices, which they commonly observed elsewhere in the refinery.”
CSB also found safety issues related to work permitting and hazard control, turnaround contractor management, and conduct of operations. According to the agency, the incident was made more severe because PEMEX Deer Park did not “adequately evaluate the hazard posed by opening equipment within an active unit that was adjacent to a unit undergoing a turnaround where many contractors were exposed to the hydrogen sulfide release.”
Refinery emergency responders took nearly an hour to reassemble the leaking flange and stop the release. In addition to the two workers who died, 13 others were transported to local medical facilities, and dozens more were treated at the scene. Two cities neighboring the refinery issued shelter-in-place orders.
The new report contains several safety recommendations for both PEMEX Deer Park and the American Society of Mechanical Engineers (ASME), a nonprofit professional organization whose mission in part includes developing codes and standards for the engineering community. One of CSB’s recommendations to PEMEX Deer Park is to label all piping in accordance with the standard ANSI/ASME A13.1, Scheme for the Identification of Piping Systems. The agency urges ASME to develop written guidelines for marking equipment for opening.
“The guidelines should define a standard practice for equipment marking that includes clear identifiers of the area to be opened and means to remove the markings at the conclusion of the work,” CSB explains.
For more information, read CSB’s news release or download the final report (PDF).