U.S. federal regulators have determined that a lack of safeguards during a maintenance shutdown led to a 2018 explosion at an oil refinery in Superior, Wis.
The U.S. Chemical Safety Board released a final report last week on the April 2018 explosion at the refinery, Wisconsin Public Radio reported Wednesday.
Calgary-based Husky Energy owned the refinery at the time of the explosion.
The blast injured 36 workers. Fears of a hydrofluoric acid leak forced 2,500 residents to evacuate. No acid leaked but a tank containing hot asphalt spilled 17,000 barrels into the facility. The asphalt caught fire, sending up a plume of black smoke that released thousands of pounds of flammable hydrocarbon vapour.
The explosion caused about $550 million US in damage to the refinery.
According to the CSB report, the refinery was shutting down a gasoline-making unit when the explosion occurred.
Investigators determined that the facility failed to implement safeguards such as creating a steam barrier in a fluid catalytic cracking unit used to make gasoline and having operators purge air from equipment within the system. A slide valve that allowed air to flow into the unit was severely eroded.
Refinery workers didn’t understand how to shut down operations and the facility failed to maintain worker training and safety information on the fluid catalytic cracking unit.
Workers also had no knowledge of a similar incident that occurred at a refinery in Torrance, Calif., that could have helped prevent the blast, according to the report.
The CSB issued 16 safety recommendations, including developing a program to ensure integrity of slide valves and worker training on fluid catalytic cracking units. Reg Curran, a spokesperson for Cenovus Energy, which now owns the refinery, said the company has incorporated all of the recommendations as it continues to rebuild the facility.
The Chemical Safety Board originally planned to release the report in 2019, but the agency has been dealing with a backlog of investigations as well as understaffing.
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