Superior Refinery Explosion Incident Overview

Date: April 26, 2018
Location: Superior, Wisconsin

Key Incident Details

• Explosion: Occurred during maintenance shutdown.
• Fire: Ignited after asphalt tank punctured.
• Injuries: 36 workers injured.
• Damage: Estimated at $550 million.
• Vapor Release: 39,000 pounds of flammable hydrocarbons released into the air.
• Evacuations: Over 2,500 residents evacuated; Duluth, MN issued shelter-in-place order.
• Safety Near-Miss: Incident considered a serious near-miss regarding hydrofluoric acid (HF) storage tank, which was fortunately not compromised.

Incident Timeline

• Before 6 a.m.: Operators began shutting down the FCC unit for maintenance.
• 10 a.m.: Hazardous air-hydrocarbons mixture ignites, leading to explosion.
• 12 p.m.: Asphalt ignites; fire spreads through refinery.
• 7 p.m.: Fire extinguished using dry chemicals and water.

Safety Issues Identified by CSB

1. Transient Operation Safeguards:

   • Shutdowns are known as transient operations, posing unique hazards.
   • Critical safeguards, such as a reactor steam barrier, were not implemented.
   • Procedures incorrectly instructed to maintain higher pressure in the regenerator instead of the reactor, allowing air to flow into the reactor.

2. Process Knowledge:

   • Minimal engagement with external expertise for FCC unit's transient operations.
   • Operating procedures lacked technical review for 25 years; errors led to dangerous conditions.

3. Process Safety Management Systems (PSM):

   • PSM systems were inadequate; did not effectively identify transient operation hazards.
   • Lack of proper operator training and unclear operating instructions contributed to the incident.

4. Industry Knowledge and Guidance:

   • Failure to apply lessons learned from similar incidents in the industry.
   • No common safety expectations or guidance for FCC units available to operators.

5. Brittle Fracture During Extreme Events:

   • Vessels constructed from outdated steel grade failed by brittle fracture.
   • Improved materials could reduce the risk of dangerous projectiles during explosions.

6. Emergency Preparedness:

   • The vicinity of HF storage tank at risk; incident treated as a near-miss.
   • Poor initial response to asphalt spill contributed to escalation of fire.

Recommendations from CSB

• For Cenovus Energy (new owner):

  • Establish safeguards and incorporate them into written procedures for FCC unit operations during transient states.
  • Develop a knowledge-sharing network across refineries for FCC technology.

• For OSHA:

  • Create guidance documents for process hazard analysis during transient operations.

• For American Petroleum Institute:

  • Develop a technical publication on safe FCC unit operations with lessons learned from investigations.

• For EPA:

  • Prioritize inspections of FCC units in refineries that operate HF alkylation units.

Conclusion

• The Superior Refinery incident highlights the critical need for proper safeguards and procedures during transient operations.
• Other refineries must learn from this incident to prevent similar disasters.