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Midland Resource Recovery Explosion

Overview

On May 24, 2017, an explosion occurred at the Midland Resource Recovery (MRR) facility in Philippi, West Virginia, killing two workers and severely injuring another worker. On June 20, 2017, while the CSB was investigating the first incident, the MRR facility experienced a second explosion that fatally injured a contractor employed by Specialized Professional Services, Inc. (SPSI). The CSB determined that the probable cause of these incidents was reactive, unstable chemicals that exploded when workers tried to drain the uncharacterized, chemically treated liquid from natural gas odorizer equipment. MRR lacked an effective safety management system to identify and control hazards from reactive chemicals.

Incident Snapshot

Field Value
Facility / Company Midland Resource Recovery (MRR)
Location Barbour County, WV; Philippi, West Virginia
Incident Date 05/24/2017
Investigation Status The CSB's final investigation report was released on December 17, 2019.
Accident Type Reactive Incident
Final Report Release Date 12/17/2019

What Happened

  • In 2006, Midland Resource Recovery (MRR) began operations at its headquarters in Philippi, West Virginia.
  • On May 24, 2017, two workers were assigned to drain some of the chemically treated MP odorizers.
  • At 11:08 a.m. on May 24, 2017, while personnel were working on the odorizer, the top tank of the MP odorizer violently exploded, killing one worker and the company owner, and severely injuring the other worker.
  • Following the May 24, 2017 explosion, CSB investigators began reviewing literature on explosive chemistry.
  • On June 20, 2017, MRR planned to drain the remaining MP odorizers and hired SPSI to conduct this activity.
  • SPSI opened valves on an MP odorizer, a pressure surge occurred, pressurized liquid flowed through the hose toward the tote, and the MP odorizer exploded less than five minutes after draining began.
  • Following the June 20, 2017 incident, the CSB terminated all planned and future activities at the MRR Philippi site to protect the safety of CSB investigators.
  • Following the second incident, MRR hired Specialized Response Solutions (SRS) to vent and drain the liquid from the remaining 11 MP odorizers.
  • The explosive venting work to drain and dispose of these vessels took place during a two-week period from December 4 to December 15, 2017.

Facility and Process Context

  • MRR provides many services related to natural gas odorants, known as mercaptans, to the natural gas and propane industry.
  • MRR decommissioned and removed odorizer equipment from sites in the United States and Canada, and transported this equipment to its Philippi, West Virginia, site for chemical treatment to remove the mercaptan odor from the steel before it was scrapped.
  • MRR also treated odorizer equipment at its site in Midland, Texas.
  • At the time of the May 24, 2017 incident, MRR had 14 employees at its Philippi site.
  • Peerless MP Odorizers are constructed of three tanks with interconnected piping.
  • The top tank is the storage tank that contains mercaptan to be introduced to the pipeline.
  • The middle tank is the odorizer compartment, where unodorized natural gas enters the tank, is odorized, and exits the tank to be routed back to the pipeline.
  • The bottom tank is a safety tank, providing overflow protection for both the top and middle tanks.
  • The odorizers involved in both the May 24, 2017 and June 20, 2017 incidents were MP 85 units, with a nominal odorant capacity of 85 gallons.
  • The MP odorizer involved in the May 24, 2017 explosion came from Kansas, where it was used to odorize natural gas in an intrastate pipeline.
  • The tank was taken out of odorant service in 1997 and sat in a lay down yard in Kansas for 18 years.
  • It was brought to the MRR Philippi site in December 2015.
  • A specification plate found at the scene indicates that the MP unit was manufactured in 1960 and had a design pressure of 550 psig and a test pressure of 825 psig.
  • The MP odorizer involved in the June 20, 2017 explosion was removed from a site in Wisconsin in November 2016 and it was chemically treated on May 15, 2017.
  • MRR decommissions up to 20 Peerless MP Odorizers per year.
  • In early 2017, MRR had accumulated 16 MP odorizers at its Philippi site that needed chemical treatment.
  • Philippi had a few years’ worth of accumulated MP odorizer inventory on site at the time of the May 24, 2017 incident.

Consequences

  • Three fatalities total: two workers on May 24, 2017, and one contractor on June 20, 2017.
  • One worker was severely injured on May 24, 2017.
  • The document states that mercaptan residue can enter the surrounding air during scrap processing and that even small quantities can raise false concerns of gas leaks and cause odor complaints; it also states that no smoke or flame were seen in the May 24 incident and that a brown mist consistent with process water was seen. Specific environmental release quantities are not provided.
  • The top tank of the MP odorizer violently exploded on May 24, 2017. The June 20, 2017 explosion ruptured the back portion of the middle chamber, blew off the front threaded section, and expelled the aluminum tray and mechanical parts. The explosion destroyed the aluminum pan and components inside the middle chamber of the May 24 odorizer.
  • The CSB terminated all planned and future activities at the MRR Philippi site after the June 20, 2017 incident. MRR later changed its odorization equipment treatment process and asserted it stopped using reactive chemicals including sodium hypochlorite.

Key Findings

Immediate Causes

  • The CSB determined that the probable cause of these incidents was reactive, unstable chemicals that exploded when workers tried to drain the uncharacterized, chemically treated liquid from natural gas odorizer equipment.
  • The document states that it is likely the explosions were caused by uncontrolled chemical reactions.

Contributing Factors

  • MRR had no formal hazard identification process in place to analyze or characterize what chemicals were inside the odorizer vessels—and in what quantity—before decommissioning and chemically treating this equipment with sodium hypochlorite.
  • MRR lacked effective safeguards to prevent unexpected or uncontrolled chemical reactions.
  • MRR technicians do not perform any testing to analyze or characterize what chemicals are present in the MP odorizer.
  • MRR technicians do not have a way to remove all the uncharacterized liquid from the bottom chamber or the middle chamber.
  • MRR had no formal procedure addressing how to chemically treat and drain the MP odorizers.
  • The MP odorizers were completely filled with liquid.
  • MRR did not install pressure relief on the tanks because the company thought it was not needed.
  • MRR allowed the MP odorizers to sit for over a month, potentially allowing unstable chemicals to form.
  • MRR lacked controls, such as established limits for how long to keep the MP odorizers full of sodium hypochlorite to control for any unintended chemical reactions.
  • MRR did not control the sodium hypochlorite dilution.
  • Workers established the dilution quantities roughly, based on estimating the volume of large, partly filled totes.
  • MRR sometimes used rainwater recovered from the ground inside tank containment areas instead of city water to dilute the hypochlorite.
  • No formal or documented risk assessment was conducted before MRR began its decommissioning process for odorant equipment.
  • No formal or documented risk assessment was done before establishing the MP odorizer decommissioning process.
  • No compatibility studies were completed prior to treating equipment.
  • MRR conducted no studies to determine the exothermic rates of reaction for adding different solutions of bleach to different mercaptan odorant mixtures.
  • No modeling was conducted to attempt to understand what was occurring within the vessels during the decommissioning process.
  • No written procedure was developed to detail how to chemically treat or safely decommission MP odorizers.
  • The only procedure was for a generic storage tank.
  • The protocol SPSI developed to drain the process water from the MP odorizers does not mention the concrete barriers, establish any type of exclusion zone near the MP odorizer, or suggest that SPSI workers would use the concrete barriers as a safeguard while performing the work.
  • The confusion surrounding the purpose of the concrete barriers alone should have been enough for MRR and SPSI to pause, reevaluate the work plan using the hierarchy of controls, and reconsider using explosive charges to protect people from being in the work area adjacent to the imminent hazard posed by these chemically treated MP odorizers.

Organizational and Systemic Factors

  • MRR lacked an effective safety management system to identify and control hazards from reactive chemicals.
  • MRR’s lack of robust process safety management systems and inconsistent operational practices made it difficult for the CSB to understand what specific reactive chemistry occurred.
  • MRR’s failure to understand and manage its reactive chemistry hazards led to both the May 24, 2017, and June 20, 2017, incidents.
  • MRR had no formal hazard identification process in place.
  • MRR had no formalized safeguards in place to prevent uncontrolled reactions.
  • MRR had no formal analysis to determine how to chemically treat MP odorizers differently than single storage tanks.
  • MRR did not conduct a Management of Change for the deviation of filling MP odorizers completely.
  • MRR’s vice president of operations stated that when such vessels were in odorizing service, the industry often treated them as an extension of the process, which therefore did not require additional protection from a pressure relief device.
  • MRR asserted attorney work product over what SPSI had learned about the May 24, 2017 incident and over SPSI’s research and theories on the cause of the incident.
  • MRR legal counsel delayed the delivery of SPSI’s protocol for draining process water from remaining MP odorizers to the CSB until the investigators were in travel status from Denver to Philippi.
  • MRR counsel controlled the sign in log sheet upon entry and prevented a frank and open discussion between the CSB and SPSI about why SPSI believed their planned activities could be performed safely.
  • MRR’s vice president of operations was aware of potential customer practices in which methanol might be added or customers might dilute odorant with diesel or kerosene.
  • Other MRR employees were either unaware of the potential for methanol, diesel, or kerosene to be present in the odorization equipment or were unaware that these chemicals could form explosive compounds when mixed with sodium hypochlorite.

Failed Safeguards or Barrier Breakdowns

  • No formal hazard identification process was in place to understand reactive hazards in decommissioning process.
  • No formalized safeguards were put in place to prevent uncontrolled reactions.
  • At no point in time were the contents inside vessels tested to check what chemicals were present prior to decommissioning or chemically treating.
  • No testing was conducted to determine the heat of reaction of the decommissioning process or to understand reaction byproducts.
  • No risk assessment (PHA) was conducted for the MP chemical treatment process, and no formalized risk assessment was conducted for chemically treating any vessels.
  • No modeling was conducted to attempt to understand what was occurring within the vessels during the decommissioning process.
  • No formal analysis was conducted to determine how to chemically treat MP odorizers differently than single storage tanks.
  • No written procedure was developed to detail how to chemically treat or safely decommission MP odorizers.
  • The MP odorizers were filled completely, which was a deviation from the normal process, but no Management of Change was conducted.
  • No overpressure protection was provided for the pressure vessels.
  • MRR did not install pressure relief on the tanks because the company thought it was not needed.
  • The protocol SPSI developed did not mention the concrete barriers, establish any type of exclusion zone near the MP odorizer, or suggest that SPSI workers would use the concrete barriers as a safeguard.
  • The CSB could not determine the exact actions of the three personnel leading up to the May 24 explosion because there were no immediate witnesses, and surveillance footage could not be used to determine their actions definitively.

Recommendations

  1. Recommendation ID: 2001-01-H-R1
    Recipient: Occupational Safety and Health Administration
    Status: reiterated in this report
    Summary: Amend the Process Safety Management Standard (PSM), 29 CFR 1910.119, to achieve more comprehensive control of reactive hazards that could have catastrophic consequences.

  2. Recommendation ID: 2001-01-H-R3
    Recipient: Environmental Protection Agency (EPA)
    Status: reiterated in this report
    Summary: Revise the Accidental Release Prevention Requirements, 40 CFR 68, to explicitly cover catastrophic reactive hazards that have the potential to seriously impact the public, including those resulting from self-reactive chemicals and combinations of chemicals and process-specific conditions. Take into account the recommendations of this report to OSHA on reactive hazard coverage. Seek congressional authority if necessary to amend the regulation.

Key Engineering Lessons

  • Reactive, unstable chemicals can be generated or remain present in decommissioned odorizer equipment when the contents are not characterized before chemical treatment and draining.
  • Chemical treatment and draining of MP odorizers required formal hazard identification, compatibility evaluation, and a written procedure specific to the equipment and process, not a generic storage-tank procedure.
  • Completely filling the MP odorizers with sodium hypochlorite without Management of Change, reaction-rate studies, or controls on dilution and residence time created conditions for uncontrolled chemical reactions.
  • Pressure relief and other safeguards were not provided because they were thought unnecessary, but the incidents show that overpressure protection and other engineered controls should have been considered for the treated vessels.
  • Work planning for draining the chemically treated MP odorizers needed to account for the actual hazard and the purpose of barriers and exclusion zones; confusion about safeguards should have triggered a pause and reevaluation using the hierarchy of controls.

Source Notes

  • All fields are limited to facts explicitly stated in the provided text.
  • Priority 1 final report information was used as the authoritative source where applicable.
  • The incident involved two explosions at the same MRR facility: May 24, 2017 and June 20, 2017.
  • The final report states that the probable cause was reactive, unstable chemicals exploding during draining of uncharacterized, chemically treated liquid from natural gas odorizer equipment.

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