The U.S. Chemical Safety and Hazard Investigation Board (CSB) released a safety video that includes simulated reenactments of the 2018 Husky Superior Refinery explosion in Superior, Wisconsin.
The video highlights the events leading up to the explosion, including the failure of a slide valve that was supposed to prevent air from mixing with hydrocarbons during a planned shutdown. It also includes a dramatic simulation of debris puncturing an above-ground storage tank, causing a stream of asphalt to flow from the tank and over a containment berm before catching fire.
CSB Chair Steve Owens explains how the incident could have been even more disastrous had the fire reached a nearby storage tank containing “highly toxic” hydrofluoric acid. The video walks viewers through CSB’s six recommendations following the conclusion of its investigation in December. “Refinery shutdowns, as well as startups, can be particularly dangerous because processes are not in normal operation mode,” Owens says in the video. “Our investigation found that critical safeguards were not in place during this shutdown, and the procedures followed at the refinery were not correct. The result was a massive explosion and fire that injured dozens of workers, caused hundreds of millions of dollars in damage, and threatened surrounding communities.”
CSB noted that the refinery relied on inadequate internal process knowledge rather than outside experts to manage the fluid catalytic cracking (FCC) unit during a planned-maintenance shutdown.
“As a result, at the time of the incident, Husky Superior Refinery employees did not adequately understand how to effectively control the FCC unit’s transient operation hazards,” wrote the CSB in a Dec. 29 news release.
CSB also concluded the refinery – now owned by Cenovus Energy after it merged with Husky Energy in 2021 – failed to maintain satisfactory process safety information, operating procedures, process hazard analyses and operator training for its FCC unit. In addition, the workers were not aware of a lesson trade groups distributed regarding FCC safety after a similar incident occurred in California in 2015.
Other actions the refinery failed to implement include transient operation safeguards, such as the separation of air from flammable hydrocarbons to prevent an explosive mixture. CSB also noted structural issues, including failure of the primary absorber and sponge absorber vessels due to a brittle fracture “or shattering like breaking glass, which sent more than a hundred pieces of metal debris throughout the refiner – some striking an asphalt tank.”
The incident injured 36 workers, caused roughly $550 million in damage to the facility and released 39,000 pounds of flammable hydrocarbon vapor into the air. Over 2,500 residents of the City of Superior were evacuated from their homes, and the City of Duluth, Minnesota, issued a shelter in place order.