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Motiva Enterprises Sulfuric Acid Tank Explosion

Overview

On July 17, 2001, an explosion and fire occurred at the Motiva Enterprises LLC Delaware City Refinery in Delaware City, Delaware. A crew of WGI contractors was repairing grating on a catwalk in a sulfuric acid storage tank farm when hot work ignited flammable vapors in Tank 393. The tank separated from its floor, other tanks in the farm also released contents, and a fire burned for approximately one-half hour. One contract worker was killed, eight others were injured, and a significant volume of sulfuric acid was released to the environment, including release to the Delaware River.

Incident Snapshot

Field Value
Facility / Company Motiva Enterprises LLC
Location Delaware City, Delaware
Incident Date 2001-07-17
Investigation Status Final report approved on August 28, 2002.
Accident Type Hot Work - Explosion and Fire
Final Report Release Date 2002-10

What Happened

  • On July 17, 2001, an explosion and fire occurred at the Motiva Enterprises LLC Delaware City Refinery (DCR), in Delaware City, Delaware.
  • A crew of WGI contractors was repairing grating on a catwalk in a sulfuric acid (H2SO4) storage tank farm when a spark from their hot work ignited flammable vapors in one of the storage tanks.
  • The tank separated from its floor, instantaneously releasing its contents.
  • Other tanks in the tank farm also released their contents.
  • A fire burned for approximately one-half hour.
  • H2SO4 reached the Delaware River, resulting in significant damage to aquatic life.

Facility and Process Context

  • Motiva Enterprises LLC Delaware City Refinery (DCR) in Delaware City, Delaware.
  • Six storage tanks, numbered 391 through 396, were originally built in 1979 for the storage of fresh H2SO4.
  • The tanks were converted to serve as storage for spent H2SO4 by the addition of carbon dioxide (CO2) inerting and the installation of conservation pressure/vacuum vents with a flame arrestor.
  • At the time of the incident, and for some time previously, the Motiva H2SO4 regeneration system could not handle the entire load of spent acid generated in the alkylation unit.
  • DCR supplemented its regeneration capacity by using an offsite contractor.
  • The catwalk was located at the roof level of the storage tanks and provided access to the gauge hatch and to various nozzles and instruments, including inerting system controls.
  • At tank 393, the catwalk was located above the southwest section of the tank, an area that had several holes due to corrosion in both the tank roof and shell.
  • The tank farm contained six atmospheric storage tanks, each with a capacity of 415,000 gallons.
  • The tanks were not individually diked; a single secondary-containment dike surrounded the tank farm.
  • A set of drains within the dike was designed to collect spills and route them to the acid plant neutralization system.

Consequences

  • Fatalities: 1
  • Injuries: 8
  • Environmental release: Approximately 1.1 million gallons of spent H2SO4 was released; Motiva estimated that 99,000 gallons of H2SO4 was released into the Delaware River; the spill resulted in approximate fish and crab kills of 2,500 and 250, respectively.
  • Facility damage: Tank 393 separated from its floor; the adjacent tank 396 also lost its contents; the catwalk was pulled down; the spill overwhelmed the dike diversion system, spill collection system, oily water and stormwater sewers, and acid neutralization system; the foreman’s pickup truck ignited and burned; acid continued to leak from tank 394 for several weeks.
  • Operational impact: Workers were unable to enter the diked area until August 17, when the tanks were emptied–32 days after the incident; the search for Mr. Davis continued until September 18; acid continued to leak from several of the remaining storage tanks for several weeks.

Key Findings

Immediate Causes

  • A spark from the hot work ignited flammable vapors in one of the storage tanks.
  • An explosion in the vapor space of tank 393 caused the tank shell to separate from its floor.
  • The tank 393 inerting system was fundamentally incapable of maintaining the oxygen concentration in the vapor space below the level necessary for combustion.
  • The inerting system was further compromised by holes in the tank roof and shell.
  • Hot work on the catwalk near the top of tank 393 generated sparks that either entered the tank and ignited the flammable mixture inside–or contacted flammable vapors outside the tank, near one of the holes, and flashed back inside.

Contributing Factors

  • Tank 393 had a history of localized corrosion and leaks throughout the last 8 years of its life.
  • The repeated recommendations of the tank inspectors that tank 393 be taken out of service “as soon as possible” for an internal inspection were unheeded.
  • A leak in the shell of tank 393, observed in May 2001, was not repaired.
  • Management failed to recognize the imminent hazard posed by the holes in tank 393 and did not promptly initiate repairs or take the tank out of service.
  • The CO2 inerting supply to tank 393, installed in 2000, was incapable of maintaining a nonflammable atmosphere.
  • CO2 was supplied to tank 393 via a temporary hose run off the inerting system of an adjacent tank (396).
  • No engineering calculations were made to determine proper sizing for the inerting system.
  • The tank conversion was completed without review of changes by technical experts, process hazard analyses, or prestartup safety reviews–all elements of a proper MOC program.
  • Motiva scheduled and permitted hot work to be conducted above and around tanks that contained flammable vapors and had known holes.
  • After authorizing the hot work, Motiva management did not institute adequate precautions to ensure worker safety, such as continuous monitoring.
  • The Motiva refinery system for investigating Unsafe Condition Reports, informing workers about such reports, and tracking the satisfactory resolution of issues was inadequate.
  • In the 3 weeks between submittal of the Unsafe Condition Report on June 27 and the day of the incident, management did not correct the reported deficiencies or implement temporary safeguards.

Organizational and Systemic Factors

  • Motiva did not have an adequate mechanical integrity management system to prevent and address safety and environmental hazards from the deterioration of H2SO4 storage tanks.
  • Motiva engineering management and MOC systems inadequately addressed conversion of the tanks from fresh to spent acid service.
  • The Motiva hot work program was inadequate.
  • The Motiva refinery system for investigating Unsafe Condition Reports, informing workers about such reports, and tracking the satisfactory resolution of issues was inadequate.
  • The Motiva Enterprises LLC management oversight system failed to detect and hold Motiva refinery management accountable for deficiencies in the refinery’s mechanical integrity, engineering management, and MOC systems.
  • Motiva did not consider the acid tank farm to be covered by requirements of the Occupational Safety and Health Administration (OSHA) Process Safety Management (PSM) Standard (29 CFR 1910.119).
  • Motiva maintained that inventory constraints prevented taking the tank out of service.
  • After EPA identified 18 tanks that required internal inspection and after Motiva reduced its maintenance budget, the tank inspection program was reprioritized.
  • Motiva management did not pursue alternatives to accommodate the time span required for a full internal inspection.
  • There was no system by which engineering staff or metallurgical experts were tasked with identifying failure trends or assessing suitability for service.

Failed Safeguards or Barrier Breakdowns

  • Mechanical integrity
  • Engineering management
  • Management of change
  • Hot work systems
  • CO2 inerting system
  • Conservation vent with flame arrestor
  • Internal inspection of tank 393
  • Full external inspections and UTM inspections
  • Temporary safeguards after the Unsafe Condition Report
  • Continuous monitoring for flammables
  • Periodic retesting after work breaks
  • Spark control
  • Emergency venting
  • Management authorization and approval in the MOC process
  • Prestartup safety review
  • Communication of hazards to operators and contractors
  • Pressure or oxygen alarms, or flow or pressure readings

Recommendations

  1. 2001-05-I-DE-R1 | Recipient: Occupational Safety and Health Administration | Status: Closed – Reconsidered/Superseded | Ensure coverage under the Process Safety Management Standard (29 CFR 1910.119) of atmospheric storage tanks that could be involved in a potential catastrophic release as a result of being interconnected to a covered process with 10,000 pounds of a flammable substance.
  2. 2001-05-I-DE-R2 | Recipient: Delaware Department of Natural Resources and Environmental Control | Status: Open | Ensure that regulations developed for the recently enacted Jeffrey Davis Aboveground Storage Tank Act require that facility management take prompt action in response to evidence of tank corrosion that presents hazards to people or the environment.
  3. 2001-05-I-DE-R3 | Recipient: Motiva Enterprises | Status: Open | Implement a system to ensure accountability for mechanical integrity decision making. Include the following specific items: Review of inspection reports by subject area experts, such as metallurgists or equipment design engineers, to ensure adequate analysis of failure trends and suitability for intended service. Establishment of a planning system to ensure the timely repair of equipment.
  4. 2001-05-I-DE-R4 | Recipient: Motiva Enterprises | Status: Open | Review the design of existing tankage that contains or has the potential to contain flammables to ensure that, at a minimum: Inerting systems are installed where appropriate and are adequately sized and constructed. Emergency venting is provided.
  5. 2001-05-I-DE-R5 | Recipient: Motiva Enterprises | Status: Open | Ensure that management of change reviews are conducted for changes to tank equipment and operating conditions, such as Tank service and contents. Tank peripherals, such as inerting and venting systems.
  6. 2001-05-I-DE-R6 | Recipient: Motiva Enterprises | Status: Open | Revise the refinery hot work program to address the circumstances that require use of continuous or periodic monitoring for flammables.
  7. 2001-05-I-DE-R7 | Recipient: Motiva Enterprises | Status: Open | Upgrade the refinery Unsafe Condition Report system to include the following: Designation of a specific manager with decision-making authority to resolve issues. Establishment of a mechanism to elevate attention to higher levels of management if issues are not resolved in a timely manner. Identification of a means to ensure communication of hazards to all potentially affected personnel. Work with the Paper, Allied-Industrial, Chemical & Energy Workers International Union (PACE) Local 2-898 to design and implement the improved system.
  8. 2001-05-I-DE-R8 | Recipient: Motiva Enterprises LLC | Status: Closed – Acceptable Action | In light of the findings of this report, conduct periodic audits of storage tank mechanical integrity and design, Unsafe Condition Reports, hot work, management of change, and accountability systems at Motiva oil refineries. Ensure that the audit recommendations are tracked and implemented. Share the findings with the workforce.
  9. 2001-05-I-DE-R9 | Recipient: Motiva Enterprises LLC | Status: Open | to the workforce and contractors at all Motiva refineries.
  10. 2001-05-I-DE-R10 | Recipient: American Petroleum Institute (API) | Status: Closed – Acceptable Action | Work with NACE International (National Association of Corrosion Engineers) to develop API guidelines to inspect storage tanks containing fresh or spent H2SO4 at frequencies at least as often as those recommended in the latest edition of NACE Standard RP 0294-94, Design, Fabrication, and Inspection of Tanks for the Storage of Concentrated Sulfuric Acid and Oleum at Ambient Temperatures.
  11. 2001-05-I-DE-R11 | Recipient: American Petroleum Institute (API) | Status: Open | Revise API tank inspection standards to emphasize that storage tanks with wall or roof holes or thinning beyond minimum acceptable thickness that may contain a flammable vapor are an imminent hazard and require immediate repair or removal from service.
  12. 2001-05-I-DE-R12 | Recipient: American Petroleum Institute (API) | Status: Closed – Acceptable Action | Ensure that API recommended practices address the inerting of flammable storage tanks, such as spent H2SO4 tanks. Include the following: Circumstances when inerting is recommended. Design of inerting systems, such as proper sizing of inerting equipment, appropriate inerting medium, and instrumentation, including alarms.
  13. 2001-05-I-DE-R13 | Recipient: American Petroleum Institute (API) | Status: Open | to your membership.
  14. 2001-05-I-DE-R14 | Recipient: NACE International (National Association of Corrosion Engineers) | Status: Open | Work with the American Petroleum Institute to develop API guidelines to ensure that storage tanks containing fresh or spent H2SO4 are inspected at frequencies at least as often as those recommended in the latest edition of NACE Standard RP 0294-94, Design, Fabrication, and Inspection of Tanks for the Storage of Concentrated Sulfuric Acid and Oleum at Ambient Temperatures.
  15. 2001-05-I-DE-R15 | Recipient: NACE International (National Association of Corrosion Engineers) | Status: Open | to your membership.
  16. 2001-05-I-DE-R16 | Recipient: Paper, Allied-Industrial, Chemical & Energy Workers International Union (PACE) Local 2-898 | Status: Open | Work with Motiva management on the design and implementation of an improved Unsafe Condition Report program.
  17. 2001-05-I-DE-R17 | Recipient: Paper, Allied-Industrial, Chemical & Energy Workers International Union (PACE) | Status: Open | your membership.
  18. 2001-05-I-DE-R18 | Recipient: National Petrochemical and Refiners Association (NPRA) | Status: Open | your membership.
  19. 2001-05-I-DE-R19 | Recipient: Building and Construction Trades Department–AFL-CIO | Status: Open | your membership.

Key Engineering Lessons

  • Corroded storage tanks with holes in the roof or shell can release flammable vapors and create an ignition hazard during nearby hot work.
  • Inerting systems must be properly sized and constructed; a temporary hose arrangement and insufficient CO2 flow were not adequate to maintain a nonflammable atmosphere in Tank 393.
  • Changes in tank service and associated peripherals such as inerting and venting systems require management of change reviews, technical review, and prestartup safety review.
  • Storage tanks with known wall or roof holes or thinning beyond minimum acceptable thickness that may contain flammable vapor require immediate repair or removal from service.
  • Hot work near tanks containing or potentially containing flammable vapors requires effective continuous or periodic monitoring and other precautions identified in the investigation.
  • Mechanical integrity programs must include timely internal inspection, expert review of inspection findings, and prompt repair planning for deteriorating tanks.

Source Notes

  • Priority 1 final report was used as the primary authority for incident facts, causes, safeguards, and recommendations.
  • Priority 3 recommendation status documents were used only to update recommendation statuses where explicitly stated.
  • Where source documents contained truncated recommendation text, the wording was preserved as written when included in the authoritative extract.
  • The final report states the report issue date as October 2002; the metadata provided a report date of 08/28/2002, which is the approval date of the final report.

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