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Synthron Chemical Explosion

Overview

Runaway chemical reaction and vapor cloud explosion occurred at Synthron, LLC in Morganton, North Carolina. One worker was killed and 14 were injured when a runaway reaction in a 1,500-gallon batch reactor led to vapor release and explosion.

Incident Snapshot

Field Value
Facility / Company Synthron, LLC
Location Morganton, NC
Incident Date 01/31/2006
Investigation Status The CSB's final report was issued at a news conference in Charlotte, North Carolina on July 31, 2007.
Accident Type Reactive Incident
Final Report Release Date 07/31/2007

What Happened

  • The production department began preparing a 6,080 pound acrylic polymer batch the day before the incident.
  • The day shift operators blended the solvents and used some of the blend to prepare the initiator solution.
  • They added the balance to the 1,500 gallon reactor.
  • The second shift operators added some of the monomer to the reactor and held back the remainder for use later in the reaction sequence.
  • The day shift arrived on the morning of January 31 and added steam to the reactor jacket to heat the reactor to the temperature specified on the batch sheet, then shut off the steam.
  • The senior operator pumped initiator solution into the reactor to start the reaction.
  • He visually checked the flow of condensed solvent through the condenser sight glass to monitor the rate of reaction.
  • Several minutes later, the senior operator heard a loud hissing and saw vapor venting from the reactor manway.
  • The irritating vapor forced him out of the building.
  • Three other employees were also forced from the building by the release.
  • The senior operator re-entered the building wearing a respirator, and was able to start emergency cooling water flow to the reactor jacket.
  • The building exploded less than 30 seconds after he exited.

Facility and Process Context

  • The company manufactured a variety of powder coating and paint additives by polymerizing acrylic monomers in a 1,500 gallon reactor.
  • Polymerization was performed in a 1,500 gallon reactor, rated at 75 psig maximum operating pressure and designated as reactor “M1”.
  • The reactor was located in a manufacturing area adjacent to the warehouse.
  • The M1 reactor was a 1500-gallon vessel used to produce a paint additive.
  • The process normally runs at close to atmospheric pressure.
  • Condensation of the vapor was the main source of cooling for the reactor.
  • The reactor also had a jacket that could receive steam or water for additional temperature control.
  • As far as is known, the facility did not have a system to record process data from the reactor electronically.

Consequences

  • Fatalities
  • One worker died.
  • The maintenance supervisor was severely burned over most of his body and died five days later.
  • Injuries
  • 14 injured, including two seriously injured workers.
  • Administrative personnel working in an onsite trailer also suffered minor injuries.
  • Two citizens driving by the site were slightly injured.
  • About a dozen others were injured.
  • Environmental Release
  • The fires following the explosion generated thick smoke.
  • Facility Damage
  • The explosion destroyed the facility and damaged structures in the nearby community.
  • Two church buildings and a house were condemned.
  • Glass was broken up to one-third of a mile from the site.
  • The Environmental Protection Agency federalized the site under the CERCLA (Superfund) regulation, remediated the site, and eventually razed the heavily damaged structures at Synthron’s facility.
  • The manufacturing facility was essentially destroyed.
  • Nearby office structures were heavily damaged.
  • A church across the road sustained significant damage.
  • Windows in homes and cars were shattered.
  • The Synthron facility was severely damaged.
  • The roof over the reactor area partially collapsed.
  • Many remaining support columns were damaged or distorted.
  • Significant sections of the concrete floor slab collapsed.
  • The remaining structure appeared highly unstable.
  • Operational Impact
  • The facility was destroyed.
  • Synthron, LLC filed for bankruptcy under Chapter 7 of the bankruptcy laws.
  • The fires were extinguished the next day.
  • The explosion rendered the Synthron facility unsafe for entry.

Key Findings

Immediate Causes

  • The additional monomer needed into the initial charge to the reactor more than doubled the rate of energy release in the reactor, exceeding the cooling capacity of the reactor condenser and causing a runaway reaction.
  • The reactor pressure increased rapidly.
  • Solvent vapors vented from the reactor’s manway, forming a flammable cloud inside the building.
  • The vapors found an ignition source, and the resulting explosion killed one worker and injured 14.
  • From what we know right now, the explosion likely followed the release of chemical vapor from a 1500-gallon vessel, known as the M1 reactor.
  • It appears possible that on the day of the accident, an increase in pressure in the reactor led to the release of flammable vapor from a metal hatch, or “manway” on the top of the reactor.

Contributing Factors

  • a lack of hazard recognition
  • poorly documented process safety information
  • ineffective control of product recipe changes
  • a lack of automatic safeguards to prevent or mitigate the effects of loss of control over the reaction
  • improper manway bolting practices
  • poor operator training
  • inadequate emergency plans drills
  • Synthron had not identified the hazards of its reactive chemical operations.
  • No formal hazard review (also known as a process hazard analysis, or PHA) was conducted to address “What could go wrong?” during reactor operations.
  • Synthron’s training program was informal and did not include reactive hazards training.
  • Synthron had minimal safety information on its polymerization process.
  • Reaction characterization and calorimetry were not performed to establish process equipment performance requirements and operating limits for safe operations.
  • The condenser’s cooling capacity was not documented, nor could the cooling load placed on the condenser be determined with the available instrumentation.
  • Synthron employees and managers had little or no understanding of reactive hazards.
  • They had not been trained on, and did not understand, the margin of safety needed or available in their polymerization operations.
  • They had little knowledge of the sensitivity of the reactor to changes in product recipes, batch sizes, or reaction conditions.
  • The changes were not effectively reviewed and the hazards went unrecognized.
  • The superintendent placed almost all of the additional monomer for the larger batch into the initial charge of chemicals loaded into the reactor.
  • There was not enough of the lower boiling temperature aliphatic solvent available in storage.
  • The superintendent and manager decided to make up half the shortfall using the higher boiling aromatic solvent, and to run the batch with slightly less total solvent than specified in the recipe.
  • The reactor normally ran at near-atmospheric pressure, for which four clamps were thought to be adequate.
  • The condenser was badly fouled, likely reducing condenser capacity at least 25 percent.
  • The company had no program to systematically monitor and control water side fouling.
  • Synthron’s employees lacked the expertise and experience to recognize the risk posed by water side fouling of the condenser.
  • During this incident, none of the production employees evacuated to a safe location.
  • The facility Emergency Action Plan did not list events or describe situations that might necessitate a plant evacuation.
  • Operating procedure did not specify employees’ actions in the event of a chemical release or loss of reactor control.
  • Employees were not trained on the Emergency Action Plan and evacuation drills were not conducted.
  • The facility was not equipped with an emergency alarm system.
  • The reason for the increase in pressure is not currently known.
  • Determining conclusively what occurred at Synthron must await further investigation.

Organizational and Systemic Factors

  • Protex International has owned a controlling interest in Synthron since 1972.
  • Protex’ president is also president of Synthron.
  • Most of the management and operations personnel at Synthron had been on the job for less than a year, in some cases much less.
  • Synthron’s president had replaced the management team in an attempt to increase sales.
  • A variety of causes had simultaneously contributed to high operator turnover.
  • The senior operator had been brought back from retirement to provide a degree of continuity.
  • Synthron had no chemical or other engineers on staff, and none had been contracted to evaluate the hazards associated with reactive operations at the site.
  • Protex had the ability to perform detailed reaction characterization work, including reaction calorimetry, at its European facilities.
  • While two of these key management employees had degrees in chemistry, they had no previous polymerization experience and were not trained on the parent company’s process safety procedures or its testing capabilities.
  • Having little reactive chemistry background or training, they did not recognize the reactive hazards at the Morganton site.
  • Synthron had not implemented a Process Safety Management (PSM) system consistent with the requirements of the Occupational Safety and Health Administration’s (OSHA) PSM regulation (29 CFR 1910.119).
  • The site had last been inspected by North Carolina OSHA (NC-OSH) in 1996.
  • No PSM citations were issued following that inspection.
  • Following the explosion, NC-OSH proposed numerous PSM citations, which Synthron contested.
  • The parent company provided little safety oversight or support to Synthron.
  • Protex did not provide adequate reactive safety support to Synthron.
  • Synthron’s president failed to ensure that the new team he installed at the Morganton site had the requisite training, knowledge, and experience to operate the facility safely.
  • Protex did not comprehensively audit or review Synthron’s safety program.

Failed Safeguards or Barrier Breakdowns

  • the batch sheet, which was used as an operating procedure at the site
  • high pressure alarms
  • automatic emergency cooling water flow to the reactor jacket
  • automatic shut-off of initiator feed
  • automatic or remotely operated injection of “short stop” solution to stop the polymerization reaction
  • automatic or remotely operated venting or dumping of the reactor to a safe location
  • The reactor manufacturer specified 18 clamps to maintain a tight seal at the reactor maximum working pressure of 75 psig.
  • The condenser’s cooling capacity was not documented.
  • The condenser was badly fouled.
  • The facility Emergency Action Plan did not list events or describe situations that might necessitate a plant evacuation.
  • Operating procedure did not specify employees’ actions in the event of a chemical release or loss of reactor control.
  • Employees were not trained on the Emergency Action Plan and evacuation drills were not conducted.
  • The facility was not equipped with an emergency alarm system.
  • The pressure relief system was to be examined.
  • The condenser and the pressure relief system were to be examined.

Recommendations

  1. 2006-04-I-NC-R1 — Recipient: Protex International — Status: Not specified — Summary: Establish a program to ensure that reactive hazards at Protex’ U.S. facilities are managed in accordance with good industry practices. At a minimum, the program should: identify and characterize reactive hazards; implement, document, and maintain appropriate safeguards; manage changes to recipes; document and maintain safety-critical process equipment capabilities; train personnel on reactive hazards, safe operating limits, and the consequences of and responses to deviations; train personnel on emergency evacuation alarms and procedures, and conduct emergency drills; and, conduct periodic audits of program implementation to identify and address weaknesses.

Key Engineering Lessons

  • Reactive hazards must be identified and characterized before production, including reaction characterization and calorimetry to establish safe operating limits and equipment performance requirements.
  • Cooling capacity and other safety-critical process equipment capabilities must be documented and maintained, including the condenser capacity and fouling condition.
  • Recipe changes and batch-size changes must be formally reviewed for their effect on reaction behavior and process safety margins.
  • Automatic or remotely operated safeguards to prevent or mitigate loss of control should be provided where a runaway reaction can occur.
  • Emergency action plans, evacuation procedures, alarms, and drills must be in place and understood before operations involving reactive chemistry.

Source Notes

  • Priority 1 final report used to resolve conflicts and establish authoritative findings.
  • Priority 4 supporting statement used only to supplement early investigation details where not contradicted by the final report.
  • Some facts appear in multiple source sections in the provided extracts; consolidated here without adding external information.

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