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Optima Belle Explosion and Fire

Overview

At approximately 10:00 p.m. on December 8, 2020, a pressure-rated rotary double cone dryer containing sodium dichloroisocyanurate dihydrate (NaDCC dihydrate, CDB-56®) exploded at Optima Belle LLC in Belle, West Virginia. A fire followed. A toxic chlorine release occurred. One Optima Belle employee was fatally injured. Two other employees were evaluated for respiratory irritation. One Kanawha County resident reported a minor leg injury. A shelter-in-place order was issued within two miles of the site for over four hours. The CSB determined that the cause was self-accelerating decomposition of heated sodium dichloroisocyanurate dihydrate inside the dryer unit.

Incident Snapshot

Field Value
Facility / Company Optima Belle LLC
Location Belle, West Virginia
Incident Date 2020-12-08
Investigation Status The CSB's investigation was released on July 6, 2023.
Accident Type Chemical Manufacturing - Fire and Explosion Investigation
Final Report Release Date 2023-07-06

What Happened

  • On December 8, 2020, at approximately 10:00 a.m., Optima Belle employees started the first of four planned batch operations.
  • They added approximately 8,820 lbs. of CDB-56® to the dryer via the manual 10-inch charge ball valve.
  • After adding the CDB-56®, Optima Belle closed the valve, started the dryer’s rotation, reduced the dryer’s internal pressure to vacuum conditions, applied a slight nitrogen purge inside the dryer, and slowly added saturated 30 psig steam to the dryer’s jacket.
  • Throughout the day on December 8, 2020, Optima Belle and Clearon monitored the dehydration progress.
  • Optima Belle operators stopped the dryer’s rotation and heating approximately every 30 minutes to take a sample of the material.
  • Later in the day, site personnel decided to extend the time between samples to one hour.
  • By late afternoon, personnel observed that the dryer internal temperature was increasing slower than anticipated and that the product moisture content was not decreasing as expected.
  • At approximately 5:04 p.m., Optima Belle employees stopped the dryer rotation, closed the steam supply, and manually drained the dryer’s jacket.
  • At approximately 5:30 p.m., the Clearon representatives left the site for the evening.
  • At approximately 6:00 p.m., Optima Belle then restarted the dryer’s rotation and re-introduced steam to its jacket.
  • By 7:00 p.m., the internal dryer temperature began to rise as anticipated.
  • At approximately 7:30 p.m., a sample of granular material from the dryer indicated similar moisture levels as previous samples taken throughout the day (greater than 11% moisture) but failed its visual inspection.
  • At approximately 8:13 p.m., after a text message between Optima Belle and Clearon regarding the dark specks, Optima Belle stopped the steam flow to the dryer jacket, stopped the dryer’s rotation, and raised the dryer pressure to atmospheric pressure to investigate the cause of the dark specks observed in the samples.
  • At 8:37 p.m., Optima Belle had closed the dryer’s 12-inch to 10-inch reducing manual ball valve and again pulled a vacuum on the dryer.
  • Optima Belle did not restart the dryer’s rotation.
  • At approximately 9:16 p.m., Optima Belle called Clearon to discuss the possible corrosion and the plan moving forward.
  • At approximately 9:20 p.m., while the dryer temperature continued to rise without the application of steam to the jacket, the main scrubber’s pH dropped below 8.
  • At approximately 9:30 p.m., Optima Belle and Clearon agreed during a telephone call to stop the batch operation for the night and continue troubleshooting the black specks in the morning.
  • Following the call, the board operator left the control room to manually open valves to stop the nitrogen blowdown to the jacket and apply cooling water.
  • At approximately 9:40 p.m., before Optima Belle could resume rotating the dryer, the dryer temperature and pressure sharply increased as the NaDCC dihydrate decomposed.
  • The last recordings in the historian data indicate the dryer temperature reached 108°C and the dryer pressure reached 33 inches of Hg before the dryer catastrophically exploded.
  • Debris and metal projectiles from the exploded dryer struck a nearby methanol pipe owned by another site tenant, and the releasing methanol caught fire.
  • Metal fragments were also found off-site on U.S. Route 60 and roughly a half mile from the site.

Facility and Process Context

  • Optima Belle LLC operated as a chemical toll manufacturer and tenant at The Chemours Company Belle site in Kanawha County, West Virginia.
  • Optima Belle was dehydrating CDB-56® on behalf of Clearon Corporation through a contractual agreement with Richman Chemical Inc.
  • The process used a pressure-rated rotary double cone dryer for dehydration of sodium dichloroisocyanurate dihydrate.
  • The dryer was operated under vacuum with a slight nitrogen purge and indirect steam heating through the dryer jacket.
  • The facility used a distributed control system (DCS), condenser, scrubber, eductor, and vacuum system as part of the batch dehydration operation.
  • Clearon had extensive process knowledge and experience with a fluidized bed dryer, but the change to a pressure-rated rotary dryer was not evaluated in a change management review.
  • Clearon reviewed and provided comments on the Optima Belle procedure to dehydrate CDB-56®; Revision 3 was in use at the time of the incident.

Consequences

  • Fatalities: 1 Optima Belle employee was fatally injured.
  • Injuries: 2 Optima Belle employees were evaluated for respiratory irritation; 1 Kanawha County resident reported a minor leg injury.
  • Environmental release: A toxic chlorine release occurred; vapors from the scrubber went into the atmosphere; debris was found almost a half mile from the site.
  • Facility damage: Optima Belle’s estimated property damage from the incident is $33.1 million.
  • Operational impact: The explosion prompted local authorities to issue a shelter-in-place order for the region within two miles of the Optima Belle site for over four hours.

Key Findings

Immediate Causes

  • The CSB determined that the cause of the Optima Belle rotary dryer’s over-pressurization and its ultimate explosion was a self-accelerating decomposition of heated sodium dichloroisocyanurate dihydrate inside the dryer unit.
  • Excessive pressure produced by the NaDCC dihydrate decomposition reaction caused over-pressurization of the Optima Belle rotary dryer and its subsequent catastrophic failure.

Contributing Factors

  • Clearon Corporation’s failure to transmit sufficient process safety information to Optima Belle.
  • Clearon’s and Optima Belle’s ineffective process safety management systems.
  • Poor knowledge management.
  • Failure to follow existing industry guidance for toll manufacturing.
  • Insufficient regulatory coverage of reactive hazards.
  • Optima Belle did not adequately understand the potential for, analyze the hazards of, or detect and mitigate the self-accelerating thermal decomposition reaction.
  • The dryer pressure relief system was not sized for an NaDCC dihydrate decomposition and was unable to evacuate the generated gas at a sufficient rate to prevent the pressure in the dryer from increasing beyond the dryer’s maximum allowable working pressure.
  • Optima Belle’s jacket cooling and heating system design lacked automatic engineering controls to monitor and adequately control the dryer temperature during the CDB-56® dehydration.
  • Optima Belle incorrectly believed that steam generation was the only credible over-pressurization hazard applicable to the dryer during the CDB-56® dehydration because it believed that decomposition was not possible using the heating medium selected for the dehydration process.
  • Optima Belle failed to adequately close out a PHA action item to review the pressure relief sizing for a self-accelerating decomposition reaction.
  • Neither Optima Belle, RCI, nor Clearon utilized available thermal and reactivity assessment tools, including the preliminary screening, calorimetry testing, or mathematical or tabular methods for CDB-56®.
  • Clearon’s Technology Package, including particularly Clearon’s NaDCC dihydrate SDS, was inadequate and lacked critical information on the decomposition of NaDCC dihydrate.
  • Clearon lacked effective process knowledge management practices.
  • Optima Belle did not have or seek out sufficient NaDCC dihydrate calorimetry data to perform cooling calculations.
  • The difference in design between the fluidized bed dryer and the rotary dryer and the different effects it could have on the material were not thoroughly evaluated by Clearon, Optima Belle, or RCI.
  • Optima Belle did not believe NaDCC dihydrate decomposition due to overheating to be a credible scenario.
  • Optima Belle’s ineffective hazards assessment was due in part to the lack of adequate process knowledge.

Organizational and Systemic Factors

  • Clearon had no formalized processes or procedures to collect and transmit PSI to contract tolling manufacturers.
  • Clearon did not have a formalized, documented process or procedure by which it generated or maintained its NaDCC dihydrate Technology Package.
  • Clearon’s ineffective systems did not ensure that essential employees had critical process knowledge and data.
  • Neither Optima Belle, RCI, nor Clearon had a formalized policy or practice for assessing thermal or reactive properties at the time of the incident.
  • Neither Optima Belle nor RCI utilized available thermal and reactivity assessment tools.
  • Clearon did not provide the 1989 Olin paper or other relevant CDB-56® data in the Technology Package.
  • Clearon’s SDS for NaDCC dihydrate was inadequate in multiple ways, including not accurately reflecting decomposition temperatures and not listing chlorine or NCl3 as decomposition products.
  • Optima Belle and Clearon essentially conducted an experiment on a new method to remove water of hydration from the CDB-56® at full production scale without first experimenting at the laboratory and pilot scales.
  • Clearon and Optima Belle never performed scale-up studies for the dehydration of CDB-56® in a pressure vessel.
  • Clearon did not substantively participate in the PHA, contrary to industry good practice guidance.
  • Optima Belle’s batch drying process was not subject to regulation by either the OSHA PSM standard or the EPA RMP rule.
  • Optima Belle’s process safety management procedure stated, “New processes are evaluated before startup to determine if they will be covered under the PSM standards.”
  • Neither Clearon nor Optima Belle adequately followed existing industry guidance concerning the safe conduct of tolling operations.
  • RCI served no role other than to connect Clearon with Optima Belle and to ensure that a Technology Package was received from Clearon.
  • The CSB found no evidence that RCI took any part in reviewing or verifying the adequacy of the Technology Package, conducting the PHA, or any subsequent tolling activities.
  • Optima Belle incorrectly believed that it had developed an inherently safe process that was incapable by design of achieving the conditions that would lead to the decomposition of CDB-56®.

Failed Safeguards or Barrier Breakdowns

  • The dryer’s pressure safety valve and rupture disc in series were inadequate to prevent over-pressurization during the decomposition reaction.
  • The jacket cooling and heating system did not contain high-temperature rise alarms, rate of change of temperature over time alarms, or interlocks to control the dryer temperature.
  • Optima Belle did not apply cold water to the jacket and did not apply a vacuum while the dryer’s rotation was stopped, contrary to the Emergency Shutdown Procedure.
  • Optima Belle did not restart the dryer’s rotation after stopping it during troubleshooting.
  • Optima Belle did not perform calculations to verify that the dryer’s cooling system could remove sufficient heat in the event of a potential CDB-56® decomposition reaction.
  • Optima Belle did not perform calculations to verify whether the dryer’s relief system was sufficiently sized to remove decomposition gases.
  • Optima Belle did not document its review process of the 3-inch PSV for the CDB-56® dehydration, including existing sizing calculations and over-pressurization scenario evaluations.
  • Optima Belle did not perform new PSV sizing calculations for the CDB-56® dehydration.
  • Clearon’s CDB-56® SDS did not communicate the material’s hazardous decomposition reaction potential.
  • Clearon’s Technology Package lacked the 1989 Olin paper and other relevant CDB-56® data.
  • Neither Optima Belle, RCI, nor Clearon performed small- or pilot-scale tests to dehydrate CDB-56® using the rotary dryer process.
  • The process did not include automatic engineering controls to monitor and adequately control the dryer temperature during the CDB-56® dehydration.
  • The scrubber pH drop was an indication that decomposition was likely occurring in the dryer, but the event was not effectively mitigated.
  • Clearon’s SDS did not accurately reflect the temperatures at which the compound could decompose.
  • Clearon’s SDS did not contain Clearon’s storage temperature restriction of 60℃.
  • Clearon’s SDS did not list chlorine or NCl3 in the list of decomposition products.
  • Clearon’s SDS stated that hazardous reactions “Will not occur” despite listing incompatible chemicals and hazardous decomposition products.
  • Clearon’s SDS did not list the material as an oxidizer despite it being classified as such by the NFPA.
  • Optima Belle’s existing heating and cooling systems could not prevent a CDB-56® decomposition as designed.
  • Optima Belle’s jacket cooling system design was likely inadequately sized to control a CDB-56® decomposition.
  • Optima Belle’s jacket heating and cooling system design lacked automatic engineering controls to monitor and adequately control the dryer temperature during the CDB-56® dehydration.
  • No analysis was performed to determine the pressure safety valve (PSV) size needed to prevent over-pressurization during a CDB-56® self-accelerating decomposition reaction.
  • The difference in design between the fluidized bed dryer and the rotary dryer and the different effects it could have on the material was not thoroughly evaluated by Clearon, Optima Belle, or RCI.

Recommendations

  1. 2021-02-I-WV-R1 | Recipient: Optima Belle LLC | Status: Closed – Acceptable Action | Summary: Develop and implement a written thermal and reactive hazards evaluation and management program. The program should adhere to industry guidance provided in publications such as the Center for Chemical Process Safety’s Essential Practices for Managing Chemical Reactivity Hazards. At a minimum, the program should identify the process that Optima Belle will use to manage chemical reactivity hazards, resources for collecting and assessing reactivity hazards, steps for determining how and when to test for chemical reactivity, documentation requirements, and training.
  2. 2021-02-I-WV-R2 | Recipient: Optima Belle LLC | Status: Closed – Acceptable Action | Summary: Develop and implement a written program for tolling process design and equipment selection using guidance from the Center for Chemical Process Safety’s Guidelines for Risk Based Process Safety and Guidelines for Process Safety in Outsourced Manufacturing Operations to ensure that: a) equipment design basis is adequate for any new tolling process or product; b) safeguards and ancillary equipment are considered and adequately designed, installed, and function as designed and required; and c) new processes are evaluated for potential process hazards at the laboratory and/or pilot scale before production scale. This written program should incorporate the information developed in Optima Belle’s thermal and reactive hazards evaluation program (see CSB recommendation 2021-02-I-WV-R1) to ensure that chemical hazards are fully understood and controlled.
  3. 2021-02-I-WV-R3 | Recipient: Optima Belle LLC | Status: Closed – Acceptable Action | Summary: Develop and implement a formalized program for the development of toll manufacturing agreements using resources such as the Center for Chemical Process Safety’s Guidelines for Process Safety in Outsourced Manufacturing Operations and Guidelines for Risk Based Process Safety. Ensure that the program provides for the following: a) Identification of roles and responsibilities of all parties, including the client, toller, and any third-party technical service providers, for all phases of a proposed arrangement; b) Evaluation of equipment requirements/specifications to ensure that they are adequate for intended operation; and c) Participation by all parties in the tolling process development, including process hazards analysis and emergency planning, and appropriate stages of the pre-planning, pre-startup, and production phases.
  4. 2021-02-I-WV-R4 | Recipient: Optima Belle LLC | Status: Closed – Acceptable Action | Summary: Develop and implement a process safety management system consistent with industry guidance publications such as is contained in the Center for Chemical Process Safety’s Guidelines for Risk Based Process Safety. At a minimum, the process safety management system should address hazard identification, risk analysis, and management of risk.
  5. 2021-02-I-WV-R5 | Recipient: Clearon Corporation | Status: Open – Unacceptable Response/No Response Received | Summary: Develop and implement a comprehensive process knowledge management program or evaluate and revise existing process safety management procedures to ensure consistency with industry guidance publications such as the Center for Chemical Process Safety’s Guidelines for Risk Based Process Safety. The program should: a) assign specific responsibilities for compiling content and maintaining robust process technology and safety information packages that incorporate relevant knowledge for all hazardous processes and substances operated, manufactured, and/or handled by Clearon Corporation; b) ensure that key process personnel are aware of critical reactive chemistry information, including thermal stability and calorimetry data, chemical compatibility information, and descriptions of any past reactive incidents and safety studies involving the materials; and c) define procedures for the transmittal of such information to toll manufacturers.
  6. 2021-02-I-WV-R6 | Recipient: Clearon Corporation | Status: Open – Unacceptable Response/No Response Received | Summary: Update the sodium dichloroisocyanurate dihydrate (CDB-56®) safety data sheet. At a minimum, the document should: a) provide the underlying reasoning for the storage temperature maximum and the consequences of exceeding that temperature; b) provide the underlying reasoning for the decomposition temperature and the consequences of exceeding that temperature; c) explain or make clear the reason(s) for and/or the circumstance(s) resulting in the differences between the decomposition temperature and the lowest temperature at which self-accelerating decomposition may occur; and d) provide the exothermic decomposition energy in the Physical Properties section.
  7. 2021-02-I-WV-R7 | Recipient: Clearon Corporation | Status: Open – Unacceptable Response/No Response Received | Summary: Develop and implement a written program for tolling process design and equipment selection using resources such as the Center for Chemical Process Safety’s Guidelines for Process Safety in Outsourced Manufacturing Operations and Guidelines for Risk Based Process Safety to ensure that: a) equipment design basis is adequate for any new tolling process or product; and b) safeguards and ancillary equipment are considered and adequately designed, installed, and function as designed and required.
  8. 2021-02-I-WV-R8 | Recipient: Clearon Corporation | Status: Open – Unacceptable Response/No Response Received | Summary: Develop and implement a formalized program for the development of toll manufacturing agreements using resources such as the Center for Chemical Process Safety’s Guidelines for Process Safety in Outsourced Manufacturing Operations and Guidelines for Risk Based Process Safety. Ensure that the program provides for the following: a) Identification of roles and responsibilities of all parties, including the client, toller, and any third-party technical service providers, for all phases of a proposed arrangement; b) Evaluation of equipment requirements/specifications to ensure that they are adequate for the intended operation; and c) Participation by all parties in tolling process development, including process hazards analysis and emergency planning, and appropriate stages of the pre-planning, pre-startup, and production phases.
  9. 2021-02-I-WV-R9 | Recipient: Clearon Corporation | Status: Open – Unacceptable Response/No Response Received | Summary: Develop and implement a process safety management system consistent with industry guidance publications such as is contained in the Center for Chemical Process Safety’s Guidelines for Risk Based Process Safety. At a minimum, the process safety management system should address hazard identification, risk analysis, and management of risk.
  10. 2021-02-I-WV-R10 | Recipient: Richman Chemical Inc. (RCI) | Status: Closed – Acceptable Action | Summary: Develop and implement a formalized program for the development of toll manufacturing agreements using resources such as the Center for Chemical Process Safety’s Guidelines for Process Safety in Outsourced Manufacturing Operations and Guidelines for Risk Based Process Safety. Ensure that the program provides for the following: a) Identification of roles and responsibilities of all parties, including the client, toller, and any third-party technical service providers, for all phases of a proposed arrangement; and b) Participation by all parties in tolling process development, including process hazards analysis and emergency planning, and appropriate stages of the pre-planning, pre-startup, and production phases.
  11. 2021-02-I-WV-R11 | Recipient: Occupational Safety and Health Administration (OSHA) | Status: Open – Awaiting Response or Evaluation/Approval of Response | Summary: Update the Chemical Reactivity Hazards website (https://www.osha.gov/chemical-reactivity) to include various reactivity assessment tools developed since the 2002 Index-Based Method for Assessing Exothermic Runaway Risk and the 2004 Preliminary Screening Method. Mathematical methods, thermal analysis methods (e.g., Accelerating Rate Calorimeter (ARC) testing), ASTM E1231-19 Standard Practice for Calculation of Hazard Potential Figures of Merit for Thermally Unstable Materials, Stoessel Criticality, and the O.R.E.O.S. Method are tools that could be considered for the update. The “Additional Resources” section of the website should also be evaluated for necessary changes and updates.
  12. 2021-02-I-WV-R12 | Recipient: Occupational Safety and Health Administration (OSHA) | Status: Open – Awaiting Response or Evaluation/Approval of Response | Summary: Following the implementation of CSB recommendation 2021-02-I-WV-R11, ensure that the chemical industry is aware of the Chemical Reactivity Hazards website (https://www.osha.gov/chemical-reactivity) by developing and implementing a comprehensive outreach plan that actively targets the chemical industry and related trade associations. The outreach plan may include such means as a national news release and OSHA’s “QuickTakes” newsletter and/or Safety and Health Information Bulletins. This outreach plan should be coordinated with OSHA’s On-Site Consultation Program partners.
  13. 2021-02-I-WV-R13 | Recipient: Occupational Safety and Health Administration (OSHA) | Status: Open – Awaiting Response or Evaluation/Approval of Response | Summary: Amend the Process Safety Management (PSM) Standard, 29 CFR 1910.119, to achieve more comprehensive control of reactive hazards that could have catastrophic consequences. Broaden the application to cover reactive hazards resulting from process-specific conditions and combinations of chemicals. Additionally, broaden coverage of hazards from self-reactive chemicals. In expanding PSM coverage, use objective criteria. Consider criteria such as the North American Industry Classification System (NAICS), a reactive hazard classification system (e.g., based on heat of reaction or hazardous gas evolution), incident history, or catastrophic potential. In the compilation of process safety information, require that multiple sources of information be sufficiently consulted to understand and control potential reactive hazards. Useful sources include but are not limited to literature surveys, information developed from computerized tools, chemical property data compiled in PubChem and the REACH dossiers maintained by the European Chemicals Agency (ECHA), chemical reactivity test data produced by employers or obtained from other sources following established standards such as ASTM E537-20, ASTM E1981-22, ASTM E2550-21, and ASTM E1231-19, and relevant incident data from the plant, the corporation, industry, and government. Augment the process hazard analysis (PHA) element to explicitly require an evaluation of reactive hazards, including rate and quantity of heat or gas generated, maximum operating temperature to avoid a runaway reaction from decomposition, Time to Maximum Rate under Adiabatic Conditions (TMRad), thermal stability of reactants, reaction mixtures, byproducts, waste streams, and products, effect of variables such as charging rates, catalyst addition, and possible contaminants, and understanding the consequences of runaway reactions or hazardous gas evolution.
  14. 2021-02-I-WV-R14 | Recipient: National Center for Biotechnology Information | Status: Closed – Acceptable Action | Summary: Update the safety information in PubChem for sodium dichloroisocyanurate (NaDCC) dihydrate, to include publicly available reactivity and decomposition information including but not limited to the Self Accelerating Decomposition Temperature (SADT), the explosion hazard when heating metal containers containing NaDCC dihydrate, and the Differential Scanning Calorimetry (DSC) and Accelerating Rate Calorimetry (ARC) results presented in this report. When compiling this information, review sources including the Registration, Evaluation, Authorization, and Restriction of Chemicals Regulation (REACH) dossier and other publications.
  15. 2021-02-I-WV-R15 | Recipient: Center for Chemical Process Safety (CCPS) | Status: Open – Acceptable Response or Alternate Response | Summary: Update Guidelines for Process Safety in Outsourced Manufacturing Operations or develop a new tolling guidance document to supplement existing guidelines. The publication should include current best practices, introduce guidance specific to tolling brokers and/or project managing companies such as Richman Chemical Inc., and cross-reference and align with the comprehensive management systems framework and terminology contained in Guidelines for Risk Based Process Safety and other contemporary industry good practice guidance.

Key Engineering Lessons

  • A change from an atmospheric fluidized bed dryer to a pressure-rated rotary dryer requires a formal change management review and re-evaluation of the process hazards.
  • Reactive hazard screening, calorimetry, and other thermal/reactivity assessment tools should be used before full-scale tolling of a new dehydration process.
  • Pressure relief systems must be sized for credible decomposition gas generation, not only for steam over-pressurization scenarios.
  • Dryer temperature control should include automatic engineering controls, alarms, and interlocks when decomposition is a credible hazard.
  • Safety data sheets and technology packages must communicate decomposition temperatures, decomposition products, and self-accelerating decomposition information clearly enough to support safe design and operation.
  • A rising scrubber pH drop and other abnormal process indicators should be treated as potential signs of decomposition and effectively mitigated.

Source Notes

  • Priority 1 final report used as the primary authority for incident facts, causal findings, and recommendations.
  • Priority 3 recommendation status summaries were used to confirm recommendation statuses and some supporting incident details.
  • Priority 4 supporting documents were used only for details explicitly stated there, including process description and timeline elements.
  • Where source documents contained conflicting or inconsistent wording, the Priority 1 final report was followed.

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