2018 Husky Energy Refinery explosion

The oil refinery in Superior, Wisconsin, which produces 50,000 barrels of oil a day, was acquired by Husky Energy from Calumet Specialty Products Partners in November 2017, retaining 180 Calumet employees. The company produces heavy oil from oil sands and conventional operations in western Canada.[3]

On the morning of the explosion, at 5:30 a.m., refinery workers were planning to shut down the Fluid Catalytic Cracking Unit (FCCU) of the refinery for routine maintenance. The FCCU is used to break down hydrocarbons from crude oil into smaller hydrocarbons, which can blend into products such as gasoline. When the FCCU is shut down, slide valves in the middle of the unit are used as a barrier between a reactor, containing flammable hydrocarbons, and a regenerator, containing air. If the hydrocarbons and air mix, an explosion can occur. On the morning of the incident, workers attempted to stop the flow of hydrocarbons to the regenerating unit, however, one of the valves was eroded, causing air to flow upward into the reactor, into equipment that contained flammable hydrocarbons.[1]

Students from Superior High School waiting for rides after being evacuated due to the explosion.

The mix of the air and hydrocarbons caused a massive explosion in the FCCU at approximately 10:00 a.m. that morning. The explosion sent debris flying 200 feet, one piece puncturing a hole in an above-ground storage tank that contained around 50,000 barrels of asphalt, causing the asphalt to spill along the ground into the refinery's main units. The asphalt ignited near additional storage tanks, eventually traveling to the FCCU of the refinery, causing a fire producing thick black smoke to travel into the air.[1] The smoke went so far into the sky, it was picked up on weather radar.[4]

The black smoke traveled southeast as far as Solon Springs in Douglas County, Wisconsin. An evacuation of the plant was ordered at 1:00 p.m., however at 2:41 p.m., an evacuation for residents 10 miles south of the plant was ordered due to concerns of the toxicity of the huge plumes of black smoke. Residents who lived 3 miles north, east, and south of the refinery were also ordered to evacuate due to concerns about the change in the direction of the wind forcing the toxic smoke above more homes, and due to concerns about the refinery's hydrofluoric acid tank causing potential further explosions and damage. Schools in the Superior School District as well as the Essentia Health-St. Mary's Medical Center in Superior was also urged to evacuate. Students were evacuated to an AMSOIL building in northwestern Superior. Schools in the Maple School District in Douglas County were also closed as a precaution. Those injured were taken to hospitals in Duluth, Minnesota.[5][6]

The fire was initially expected to burn for days. Firefighters of the Superior Fire Department didn't begin to address how to attack the fire until 3:00 p.m. that day. Firefighters put out the fires in the refinery's units, then proceeded to push the burning asphalt away from the nearby storage tanks and attack the fire with foam. The fire was fully extinguished just before 7 p.m. later that night, but the evacuation order was maintained until 6 a.m. the following day.[7]

A sign on the exterior of the plant counting the days since the plant has been the focus of an incident.

The USCSB's report of this incident is still ongoing. They released their last report on the incident in August 2018 confirming a worn-out slide valve was a factor in the explosion,[1] as well as a detailed animation of the incident with the information they concluded on December 18, 2019.[8] Husky Energy faced a class-action lawsuit against residents who were forced to evacuate their homes, citing a section from the report of the USCSB that stated that their equipment "failed to separate oxygen and hydrocarbons, allowing a flammable mixture to form."[9] Husky reach a $1M settlement in July 2021.[10] Reconstruction of the refinery began in the fall of 2019, and is expected to become fully operational in later 2022. Construction was halted in May 2020 due to the COVID-19 pandemic, but was resumed in June 2020.[11]