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ExxonMobil Baton Rouge Refinery Chemical Release and Fire

Overview

On November 22, 2016, an isobutane release and fire occurred in the sulfuric acid alkylation unit at the ExxonMobil Refinery in Baton Rouge, Louisiana. Four workers were seriously injured. The incident occurred during maintenance on a plug valve. Critical bolts were removed from the valve's pressure-retaining top-cap. The valve came apart during attempted manual operation with a pipe wrench. Isobutane was released and ignited within seconds.

Incident Snapshot

Field Value
Facility / Company ExxonMobil
Location Baton Rouge, LA
Incident Date 11/22/2016
Investigation Status The CSB's final report was released at a public business meeting in Washington, D.C. on September 18.
Accident Type Oil and Refining - Fire and Explosion
Final Report Release Date 09/18/2017

What Happened

  • On November 22, 2016, an isobutane release and fire seriously injured four workers in the sulfuric acid alkylation unit at the ExxonMobil Refinery in Baton Rouge, Louisiana.
  • During removal of an inoperable gearbox on a plug valve, the operator performing this activity removed critical bolts securing the pressure-retaining component of the valve known as the top-cap.
  • One of the operators removed the gearbox assembly so he could turn the valve stem with a pipe wrench to open the valve.
  • To remove the gearbox, the operator removed the four vertical bolts that connected the gearbox support bracket to the valve body.
  • One of the operators then opened the valve by rotating the valve stem with a pipe wrench, while the other operator observed.
  • When the operator then attempted to open the plug valve with a pipe wrench, the valve came apart and released isobutane into the unit, forming a flammable vapor cloud.
  • Pressurized isobutane escaped from the valve body, forming a flammable white vapor cloud.
  • The isobutane reached an ignition source within 30 seconds of the release, causing a fire and severely burning four workers who were unable to exit the vapor cloud before it ignited.
  • Based on surveillance video, an energized welding machine located roughly 70 feet away likely ignited the vapor cloud.
  • Emergency responders isolated the release and extinguished the fire about 25 minutes after the initial ignition.

Facility and Process Context

  • The incident occurred in the sulfuric acid alkylation unit at the ExxonMobil Refinery in Baton Rouge, Louisiana.
  • The refinery used a type of valve known as a quarter-turn plug valve for many applications in the alkylation unit, including the inlet valves to these isobutane pumps.
  • There were long-standing reliability issues with gearboxes used to operate plug valves in the refinery’s alkylation unit.
  • When alkylation unit operators encountered a malfunctioning gearbox on a plug valve, it was an accepted practice for the operator to remove the gearbox to open or close the valve with a pipe wrench.
  • Baton Rouge refinery management did not provide alkylation unit workers performing this operations activity with a written procedure or training on safe gearbox removal from plug valves and its associated hazards.
  • 15 (approximately three percent) of the roughly 500 plug valves with manually operated gearboxes in the refinery’s alkylation unit were an older design that required attaching the gearbox support bracket to pressure-retaining valve components.
  • The improved valve design involves attaching the gearbox support bracket without connecting to pressure-retaining parts of the valve, allowing for safer gearbox removal.
  • The Baton Rouge refinery replaces and does not repair inoperable gearboxes.
  • Approximately 97 percent of the plug valves located in the Baton Rouge refinery’s alkylation unit are the more recent Durco plug valve design, which secures the gearbox assembly to the valve body flanges.

Consequences

  • Fatalities: None reported.
  • Injuries: 4 workers injured; all four workers received third degree burn injuries; one ExxonMobil employee and three contractors were seriously injured.
  • Environmental release: ExxonMobil estimated that 2,000 pounds of isobutane released into the atmosphere.
  • Facility damage: The valve came apart; a fire occurred in the unit.
  • Operational impact: Emergency responders isolated the release and extinguished the fire about 25 minutes after the initial ignition.

Key Findings

Immediate Causes

  • When the operator then attempted to open the plug valve with a pipe wrench, the valve came apart and released isobutane into the unit, forming a flammable vapor cloud.
  • The isobutane reached an ignition source within 30 seconds of the release, causing a fire.

Contributing Factors

  • Failure to identify and address the older model plug valve design and gearbox reliability issues.
  • Lack of a human factors evaluation to identify the older model plug valves’ design and reliability issues as well as the potential hazards associated with operating and maintaining these valves.
  • No written procedures detailing the steps needed to remove different models of gearboxes from plug valves to manually open or close the valve safely.
  • Not training workers to safely remove the various plug valve gearbox models in the alkylation unit and the hazards associated with this type of work.
  • An organizational culture that accepted operators removing malfunctioning plug valve gearboxes despite the lack of detailed procedures and training for safe removal.
  • The support bracket appeared to be part of the gearbox, and it was not sufficiently obvious to the operator that the gearbox removal did not require removing the support bracket.
  • The design of the Baton Rouge refinery’s pre-1984 plug valves lacked dedicated connection points to attach the gearbox.
  • The location of the bolts on the newer valve design may have also contributed to the operator removing pressure-retaining bolts.
  • The refinery’s human factors analysis did not identify and control this hazard before the incident.

Organizational and Systemic Factors

  • The organizational culture at the Baton Rouge refinery accepted operators removing malfunctioning plug valve gearboxes in the alkylation unit despite the lack of detailed procedures and training.
  • ExxonMobil even acknowledged that it was “accepted practice” at the refinery alkylation unit for operators to remove malfunctioning gearboxes from plug valves and manually rotate the valve stem with a pipe wrench.
  • The long-standing gearbox reliability issues were never investigated or corrected.
  • Operators sometimes encountered inoperable gearboxes on alkylation unit plug valves and removed the gearbox to open or close the valve despite the lack of detailed written procedures and training to perform this activity safely.
  • The refinery’s human factors analysis did not identify and control this hazard before the incident.
  • In its most recent alkylation unit PHA, the Baton Rouge refinery did not document any consideration of human factors related to valve operational issues.
  • Baton Rouge refinery operators acknowledged to the CSB that they frequently encountered situations where the handwheel did not turn the valve.
  • ExxonMobil did not adequately prepare alkylation unit operators at the refinery to remove a gearbox attached to the top-cap of a plug valve safely.

Failed Safeguards or Barrier Breakdowns

  • Baton Rouge refinery management did not provide alkylation unit workers performing this operations activity with a written procedure or training on safe gearbox removal from plug valves and its associated hazards.
  • The Baton Rouge refinery did not document any consideration of human factors related to valve operational issues in its most recent alkylation unit PHA.
  • The refinery’s human factors analysis did not identify and control this hazard before the incident.
  • The company had not developed a procedure that would provide guidance to operators on how to run the unit safely for foreseeable modes of operation.
  • The lack of a procedure meant that there was no guidance on what constituted an unsafe condition and operators had no instruction on how to handle process deviations.
  • The Baton Rouge refinery should have developed written procedures detailing the appropriate steps for safely removing its various types of plug valve gearboxes.
  • The Baton Rouge refinery did not adequately prepare alkylation unit operators at the refinery to remove a gearbox attached to the top-cap of a plug valve safely.
  • The warning in Flowserve plug valve literature was not communicated to Baton Rouge refinery workers.

Recommendations

  1. Recommendation ID: Not provided
    Recipient: Companies
    Status: Not provided
    Summary: Evaluate human factors associated with equipment design and apply the hierarchy of controls to mitigate identified hazards. Establish detailed and accurate written procedures and provide training to ensure workers can perform all anticipated job tasks safely.

Key Engineering Lessons

  • Do not rely on informal workarounds for operating or maintaining equipment when the equipment design can expose workers to pressure-retaining components.
  • Equipment design should make safe removal and maintenance intuitive and should not require workers to remove pressure-retaining fasteners to perform routine operations.
  • Human factors review should be used to identify foreseeable misuse and maintenance hazards in valve and gearbox designs before incidents occur.
  • Written procedures and training must address the specific equipment variants present in the unit, including older designs with different attachment methods.
  • Warnings in manufacturer literature must be communicated to the workers who perform the task.

Source Notes

  • Consolidated from the CSB final report extract (source_priority 1) only; no lower-priority sources were needed to resolve conflicts.
  • All facts were taken directly from the provided structured extract; no external information was added.
  • The final report text used the term "accepted practice" for gearbox removal work in the alkylation unit.
  • The report described the ignition source as an energized welding machine located roughly 70 feet away, based on surveillance video.

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