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PEMEX Deer Park Chemical Release

Overview

On October 10, 2024, at approximately 4:30 p.m., a hydrogen sulfide release occurred at the PEMEX Deer Park facility’s amine recovery unit while workers were attempting to remove an isolation blind from piping that normally transports hydrogen sulfide gas. The incident caused two fatalities and 13 injuries.

Incident Snapshot

Field Value
Facility / Company PEMEX Deer Park Refinery
Location Deer Park, TX
Incident Date 2024-10-10
Investigation Status The CSB's investigation was released on February 23, 2025.
Accident Type Hydrogen sulfide release
Final Report Release Date 2026-02-23

What Happened

  • On October 3, 2024, PEMEX Deer Park shut down the Sulfur Unit and began the scheduled turnaround maintenance tasks.
  • On October 8, PEMEX Deer Park operators prepared ARU6 equipment for scheduled maintenance by emptying, depressurizing, and purging piping, closing valves, and completing equipment lock-out/tag-out (LOTO).
  • On October 8, 2024, PEMEX Deer Park issued a work permit to Repcon to install 15 blinds in the ARU6 piping.
  • On the morning of October 9, 2024, the PEMEX Deer Park operator confirmed that all the blinds were properly installed and closed Repcon’s work permit.
  • On October 10, 2024, around 7:00 a.m., Repcon day shift boilermakers arrived to continue turnaround tasks in the Sulfur Unit.
  • At 8:18 a.m., a PEMEX Deer Park operator issued a work permit to Repcon to remove the 15 ARU6 blinds in the Amine Unit.
  • Around 3:00 p.m., the Repcon boilermakers completed the blind removal at the first 13 locations and prepared to remove the final two blinds.
  • Around 3:30 p.m., the PEMEX Deer Park operator completed his shift and briefed the replacement night shift operator on the ongoing ARU work activities.
  • Before beginning work to remove the final two blinds, the Repcon boilermakers obtained supplied-air respirators and escape bottles from Code Red.
  • The two Repcon boilermakers at the Blind 407 location encountered two identical piping segments 5 feet apart.
  • Believing that they were working on Blind 407, the Repcon boilermakers began removing bolts from the ARU7 flange, which was not covered by the work permit.
  • At 4:22 p.m., portable gas monitors in the Sulfur Unit detected a hydrogen sulfide concentration above the alarm threshold of 10 ppm and alerted Code Red technicians.
  • At 4:23 p.m., the ARU7 flange bolts were disassembled enough that the flange burst open, forcefully releasing toxic hydrogen sulfide gas.
  • At 4:24 p.m., the bottle watch worker alerted PEMEX Deer Park emergency responders of the unresponsive Repcon boilermaker.
  • Between 4:24 and 4:27 p.m., console operators in the control room detected a rapid pressure decrease on the acid gas transfer lines.
  • Between 4:27 and 4:28 p.m., at least 4 minutes after the release began, the Amine Unit gas monitors detected hydrogen sulfide concentrations greater than 50 ppm, and alarms started to sound in the Amine Unit.
  • Between 4:29 and 4:34 p.m., emergency responders arrived at the Sulfur Unit and sounded the site-wide alarm at 4:35 p.m.
  • At 4:49 p.m., a console operator closed a remotely operated control valve upstream of the release and redirected upstream acid gas flow to the emergency flare system.
  • Around 5:22 p.m., emergency responders reassembled the leaking flange, stopping the release.

Facility and Process Context

  • The PEMEX Deer Park Refinery is a petroleum refinery located in Deer Park, Texas.
  • In January 2022, PEMEX acquired the entire refinery, which then became known as the PEMEX Deer Park Refinery.
  • The PEMEX Deer Park Refinery employs approximately 1,000 personnel and 1,200 contract workers during normal operations.
  • On the day of the incident, there were 1,729 contractors and personnel from other companies, as well as 252 PEMEX Deer Park employees onsite.
  • The incident occurred in the PEMEX Deer Park Refinery’s Amine Regeneration Unit (“Amine Unit”).
  • The Amine Unit includes two identical and parallel processes, designated as ARU6 and ARU7.
  • ARU6 was shut down for maintenance activities at the time of the incident, and the process piping had been depressurized, purged, and isolated.
  • ARU7 was operating normally after already having gone through the same maintenance activity the week before the ARU6 work.
  • PEMEX Deer Park called this unit status “Run-and-Maintain,” where equipment would be shut down for maintenance while parallel and redundant equipment remained operational.
  • The nearby Sulfur Unit was in a scheduled unit shutdown, called a turnaround, for planned maintenance activities.
  • Unlike Run-and-Maintain status, the Sulfur Unit was in “Positive Isolation” status, where all equipment within the unit’s boundaries is considered shut down, depressurized, decontaminated, and isolated from outside hazardous process energy.
  • At the time of the incident, contract workers from at least 10 different companies were performing various turnaround maintenance activities in the Sulfur Unit.
  • The areas containing the Amine Unit and the Sulfur Unit were equipped with permanently mounted hydrogen sulfide gas detectors with alarms.
  • The Sulfur Unit’s permanent gas detectors were not operable on the day of the incident, however, due to planned maintenance related to the Sulfur Unit turnaround.
  • The wind blew from the northeast at approximately 2 miles per hour, with gusts up to 8 miles per hour.
  • There are more than 6,400 people residing in more than 2,440 housing units within 1 mile of the PEMEX Deer Park Refinery.

Consequences

  • Two contract workers were fatally injured.
  • Thirteen additional contract workers were transported to nearby medical facilities to be evaluated for hydrogen sulfide exposure.
  • Forty-seven contractor workers from 10 companies were evaluated for hydrogen sulfide exposure.
  • An additional 13 contractors were taken to nearby medical facilities, evaluated for hydrogen sulfide exposure, and released.
  • Approximately 27,000 pounds of toxic hydrogen sulfide gas were released.
  • The report also states the incident resulted in the release of more than 27,000 pounds of hydrogen sulfide into the atmosphere.
  • PEMEX Deer Park reported property damage of $12.3 million associated with the incident, resulting from the loss of use in the Amine Unit and downstream processes.
  • The release continued for nearly an hour until emergency responders reassembled the leaking flange, stopping the release.
  • Shelter-in-place orders were issued by officials in the neighboring cities of Deer Park, Texas, and Pasadena, Texas, and remained in effect for several hours.
  • The facility was not physically damaged, but there was loss of use in the Amine Unit and downstream processes.

Key Findings

Immediate Causes

  • The cause of the incident was the opening of incorrect equipment, which released pressurized hydrogen sulfide.
  • PEMEX Deer Park did not establish an effective method to clearly identify the correct equipment to open before authorizing opening the equipment.

Contributing Factors

  • PEMEX Deer Park’s failure to 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.
  • PEMEX Deer Park deviated from several of their own policies and procedures that could have prevented the incident.
  • The boilermakers did not have the blind list or drawing; they used visual indicators to identify the location of the blinds to be removed.
  • The boilermakers observed a flange locking device on or near the ARU7 flange and believed that the ARU7 flange was the intended location of the work, unaware that Blind 407 was located on the piping segment five feet away.
  • The boilermakers removed their personal hydrogen sulfide gas detectors and placed them on the platform nearby because PEMEX Deer Park policy did not require personal gas detectors to be worn while using supplied-air respirators.
  • The wind carried the released hydrogen sulfide away from the gas detectors in the ARUs, and consequently the ARU alarms did not sound immediately.
  • The SRU hydrogen sulfide detectors were disabled due to maintenance work associated with the turnaround and did not activate.
  • There were no remotely operated isolation valves downstream of the release point capable of stopping the release.

Organizational and Systemic Factors

  • PEMEX Deer Park did not have a clearly defined system to identify equipment for opening during Run-and-Maintain operations.
  • PEMEX Deer Park’s inconsistent and uncontrolled blind tag identification system during the Amine Unit’s maintenance did not give a clear indication of what equipment was to be opened.
  • PEMEX Deer Park’s use of the Circle-X marking system added unnecessary confusion due to the inability to determine whether the marks were placed from a previous equipment opening.
  • The Amine Unit’s two different but visually identical piping systems were not distinctly labeled, and the boilermakers could not distinguish between the two different systems.
  • PEMEX Deer Park issued a work permit to Repcon that covered removing blinds with different hazards, even though its procedures prohibited the practice.
  • PEMEX Deer Park’s work permit lacked a defined hold or stop point.
  • PEMEX Deer Park did not evaluate the hazards of opening piping in the Amine Unit directly upwind of the Sulfur Unit, where many contractors were working on turnaround activities.
  • PEMEX Deer Park and Repcon did not sufficiently communicate to the boilermakers that they were being relocated from a shutdown turnaround unit to an active unit, and did not instruct the Repcon boilermakers on the requirements and precautions for working in a Run-and-Maintain unit.
  • PEMEX Deer Park did not have a robust conduct of operations practice, as shown by the frequent discrepancies between established procedures and the actions by engineering and operations personnel that contributed to the incident.
  • PEMEX Deer Park did not develop a Management of Change for the shutdown of SRU gas detectors and the use of temporary gas detectors during the SRU turnaround.
  • PEMEX Deer Park procedures required operators to develop a list of blinds and a drawing to identify blind locations.
  • PEMEX Deer Park procedures required the use of the tags and locking devices on flanges with blinds during turnaround activities, such as the work occurring at the SRU, but these are not required during non-turnaround maintenance activities, like at the ARUs.
  • Instead, PEMEX Deer Park policy required the development of an isolation list and a drawing depicting the blind locations, which the PEMEX Deer Park operator had provided to the Repcon foreman.
  • PEMEX Deer Park policy did not require personal gas detectors to be worn while using supplied-air respirators.
  • PEMEX Deer Park requires personnel to wear personal hydrogen sulfide gas detectors when entering the ARUs and SRU.

Failed Safeguards or Barrier Breakdowns

  • The written blind list and drawing did not clearly indicate where each flange to be opened was located.
  • The tag for the intended flange was placed on a platform railing above the intended flange, and the Repcon workers did not see it.
  • The Repcon boilermakers looked for either the orange-and-blue blind tags or unlocked red flange-locking devices rather than referencing the blind list or drawing.
  • The work permit stated that a PEMEX Deer Park operator would be present when opening connected piping segments to the atmosphere, but no operator was present for the Repcon removal of Blind 407.
  • The work permit’s statement “Ops present for each break” was ineffective as a stop or hold point.
  • The permit did not evaluate or control the hazards of pipe opening activities directly upwind of a unit where many other contract workers were performing scheduled maintenance activities.
  • The SIMOPs form provided no guidance on how to perform a SIMOPs evaluation or mitigate the associated hazards.
  • PEMEX Deer Park did not directly inform the Repcon boilermakers about the Amine Unit’s status or the hazards associated with the maintenance task.
  • The Repcon boilermakers removed their personal hydrogen sulfide gas detectors because PEMEX Deer Park’s policy did not require personal gas detectors to be worn while using supplied-air respirators.
  • The Sulfur Unit’s permanent gas detectors were not operable on the day of the incident due to planned maintenance related to the Sulfur Unit turnaround.
  • PEMEX Deer Park did not adhere to its auditing system, and operators were allowed to continue issuing permits without input from their supervisors.
  • The SRU’s fixed gas detectors were not operable on the day of the incident due to maintenance related to the SRU turnaround.
  • The ARU alarms did not sound immediately.
  • The SRU hydrogen sulfide detectors were disabled due to maintenance work associated with the turnaround and did not activate.
  • The boilermakers did not observe a blind identification tag on either of the ARU6 or ARU7 flanges.
  • The operator could not fully close the manual valves necessary to isolate the leak before his contained breathing air supply became low.
  • There were no remotely operated isolation valves downstream of the release point capable of stopping the release.

Recommendations

  1. 2024-05-I-TX-R1 | Recipient: PEMEX Deer Park | Status: Open – Awaiting Response or Evaluation/Approval of Response | Summary: Label all piping in ARU6 and ARU7 in accordance with ANSI/ASME A13.1 Scheme for the Identification of Piping Systems.
  2. 2024-05-I-TX-R2 | Recipient: PEMEX Deer Park | Status: Not specified | Summary: Develop procedures to ensure that any craftworkers introduced to or removed from a unit in Positive Isolation Status receive instructions that define the hazards, safeguards, and requirements of the unit associated with the work. The procedures should require each craftworker to receive clear communication on the identified hazards, control measures, and all other requirements before commencing work in a new area.
  3. 2024-05-I-TX-R3 | Recipient: PEMEX Deer Park | Status: Open – Awaiting Response or Evaluation/Approval of Response | Summary: Establish a conduct of operations system that establishes and enforces behavioral and performance metrics in accordance with CCPS’s Conduct of Operations and Operational Discipline. The system should include: a) the management commitment to process safety, b) employee input on policies and procedures, c) methods to ensure that policies and procedures can be effectively followed, to include, at a minimum: 1) permitting, 2) equipment marking, and 3) energy isolation procedures, and d) regular audits to verify adherence to conduct of operations metrics, to include, at a minimum: 1) performance expectations, 2) training, 3) management visibility, 4) leadership by example, and 5) worker knowledge and awareness.
  4. 2024-05-I-TX-R4 | Recipient: American Society of Mechanical Engineers (ASME) | Status: Open – Awaiting Response or Evaluation/Approval of Response | Summary: 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.

Key Engineering Lessons

  • Positive equipment identification for opening work must be unambiguous and not rely on visual similarity, informal markings, or assumptions by workers.
  • When identical parallel systems are present, piping and equipment labeling must clearly distinguish the correct system and location to be opened.
  • Permit-to-work and blind-marking practices should provide a clear hold point and a clear method to verify the exact equipment before opening.
  • Gas detection and alarm strategies should account for wind direction, detector placement, and the possibility that fixed detectors may be unavailable during maintenance.
  • If a release cannot be isolated quickly by manual valves, the availability of remotely operated isolation capability is a critical safeguard.
  • When workers are moved between shutdown and active units, they need explicit communication on the hazards and requirements of the new work area before starting work.

Source Notes

  • Priority 1 final report used to resolve conflicts and establish authoritative findings, recommendations, and incident sequence.
  • Priority 2 and 3 recommendation documents were used to confirm recommendation status and wording where available.
  • Priority 4 supporting documents were used only for incident details not contradicted by the final report.
  • Dates normalized to ISO format where directly supported by source text.

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