The U.S. Chemical Safety and Hazard Investigation Board (CSB) has released their final report on the April 26, 2018 Huskey Superior Refinery explosion.

The report reads, “the incident could have been prevented.”

The report states 36 refinery and contract workers were injured and sought medical attention.

The chemical disaster caused approximately $550 million in property damage.

The City of Superior evacuated 2,507 residents within 2 miles north, 3 miles to the east and west, and 10 miles south of the refinery.

Debris from the explosion could have punctured a highly toxic hydrofluoric acid storage tank, given its closer proximity to the point of explosion.

The report listed a number of things of concern that played roles into the explosion.

The concerns include safety issues, process knowledge, process safety management systems, industry knowledge and guidance, plus emergency preparedness.

Cenovus Energy the current owner of the plant released a statement to Northern News Now regarding the report:

We have incorporated all of the recommendations the Chemical Safety Board directed to the Superior Refinery into our rebuild, and they will be in place when it restarts.

These include enhanced safety processes and numerous equipment upgrades in alignment with their recommendations, including:

• New state-of-the-art slide valves in the Fluid Catalytic Cracking unit with enhanced safeguards such as advanced instrumentation to monitor performance in real-time and ensure the operations and engineering staff can carefully assess performance.
• A new control system throughout the refinery which will improve safety and operating performance through enhanced safety shutdowns and process control.
• New training materials to be delivered by subject matter experts, including the use of simulators which mirror control room equipment and cover a full range of operating conditions.

We will continue to work with the CSB as we progress the implementation of its recommendations directed to Cenovus’s U.S. operations.

We are ramping up commissioning activities towards restart in early 2023.

The CSB is an independent federal agency charged with investigating, determining, and reporting to the public in writing the facts, conditions, and circumstances and the cause or probable cause of any accidental chemical release resulting in a fatality, serious injury, or substantial property damages.

The following is sections from the Executive Summary of the explosion investigation.

Safety Issues:

* Husky Superior Refinery did not establish or maintain a reactor steam barrier between air and hydrocarbons during the FCC (fluid catalytic cracking) shutdown.

*Husky Superior Refinery did not properly purge the main column overhead receiver during the shutdown to remove oxygen from the system.

*Husky Superior Refinery relied entirely on catalyst slide valves to keep the air and hydrocarbon systems separated during the shutdown. FCC catalyst slide valves are known in most of the refining industry as insufficient safeguards to stop all flow between the air and hydrocarbon systems

*Had Husky Superior Refinery implemented the safeguards above, the incident could have been prevented

Process Knowledge:

* The refinery’s employees did not adequately understand or know how to effectively control the FCC unit’s transient operation hazards.

* Husky Superior Refinery was not aware that its FCC unit shutdown procedure was not aligned with the technology licensor’s guidance that had been in place and provided to the refinery since the unit was designed in 1960.

* Husky Superior Refinery did not perform a technical review of its FCC unit operating procedures with its process engineers, the licensor, or outside consultants for at least 25 years prior to the incident.

* Had a multidisciplinary team reviewed the operating procedures, with guidance from a subject matter expert, the technical errors and omissions could have been identified and resolved to match the process technology information provided by the licensor, and the explosion could have been prevented.

Process Safety Management Systems:

* Husky Superior Refinery did not maintain some of the FCC licensor’s critical safety technology as part of its process safety information (“PSI”) package.

* Husky Superior Refinery’s FCC unit PHA teams did not specifically evaluate the hazards of following the refinery’s most recent shutdown procedure or otherwise use a methodology that enhanced identification of transient operations hazards. As a result, the refinery did not identify, analyze, and control transient operation hazards that led to the explosion.

* The lack of known FCC-related safety concepts in the refinery’s written training manual, combined with the lack of trainer qualifications and hands-on practice opportunities, led to poor operator training and contributed to the incident.

Industry Knowledge and Guidance:

* Husky Superior Refinery incident occurred less than one year after the CSB released its investigation of another FCC unit transient operation explosion in California.

* After the CSB released its ExxonMobil Torrance Refinery investigation report and a safety video in 2017, the American Fuel and Petrochemical Manufacturers’ (“AFPM”) association helped disseminate the lessons from the ExxonMobil Torrance Refinery incident through its industry conference later that year. Despite these educational efforts, Husky Superior Refinery employees were not aware of or did not learn lessons from the ExxonMobil Torrance Refinery incident in a way that could have helped them to prevent the April 2018 incident

Brittle Fracture During Extreme Events:

* The primary absorber and sponge absorber vessels in the Husky Superior Refinery FCC unit failed by brittle fracture (shattering like breaking glass), which sent more than a hundred pieces of metal debris throughout the refinery, striking workers and operating equipment. These vessels were constructed of the American Society of Testing and Methods (“ASTM”) A-212 and A-201 grade steels, which are no longer recommended for new equipment. Had the vessels been constructed of a newer grade of steel with better toughness properties, they should have ruptured by ductile fracture (tearing open like a zipper or fish mouth) with a reduced impact on the surrounding area.

Emergency Preparedness:

* The likely ignition source that ignited the asphalt was pyrophoric material inside the storage tank that smoldered when exposed to the air that entered through the punctured tank wall. Husky… uncertainty by refinery employees about how to properly mitigate a large area of spilled hot, ignitable asphalt.

Cause:

* The CSB determined that Husky Superior Refinery explosion, which occurred during the shutdown of the FCC unit, was caused by inadvertently directing air inside the regenerator through the reactor, and the main column, and then into the gas concentration unit. As the air continued flowing into the gas concentration unit, oxygen accumulated and formed a flammable mixture inside the primary and sponge absorbers. The oxygen also reacted with existing pyrophoric material inside this equipment, creating the ignition source for the explosion.

If you would like to see the full report click HERE.

Picture from CSB Husky Superior Refinery Report(U.S. Chemical Safety and Hazard Investigation Board)


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