The initial explosion at a refinery in Superior, Wisconsin, occurred in the fluid catalytic cracking (FCC) unit, according to a senior adviser with the U.S. Chemical Safety and Hazard Investigation Board.
The FCC unit is a part of the distillation process during which crude oil is heated and extracted to create gasoline and petroleum-based products, the senior adviser said.
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The senior adviser confirmed the new information via email Thursday, stating the explosion in the FCC unit “will be one of the main focus points of the investigation,” although he said his department is “not in a position at this time to explain why the FCC failed.”
The explosion and subsequent fire at Husky Energy refinery sent plumes of smoke into the air last Thursday. A state of emergency was declared and thousands of people were forced to evacuate.
Superior Fire Chief Steve Panger said crews of 25 to 30 firefighters were battling the blaze throughout most of the operation.
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In the wake of the incident, Duluth mayor Emily Larson called on the company to eliminate hyrdrogen flouride from its refining process.
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“We welcome their investment in our economies and the good paying jobs this work provides,” Larson said in a statement. “However, choosing the known risks of hydrogen flouride is not something that is in keeping with the premise of being a good corporate partner. It elevates the danger to our environment and our people.”
In response, the company said it will consider several ideas during the rebuild process.
“The HF unit and its safety systems will be a part of the thorough investigation underway at the refinery, in conjunction with regulators,” a company statement read.
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