Duluth Mayor Emily Larson won't easily forget the day in April 2018 when a massive explosion and fire rocked the Husky Energy oil refinery in neighboring Superior, Wis., sending a towering plume of thick, black smoke into the sky, and forcing the evacuation of much of the city across the St. Louis River.
"It was a horrifying feeling," she recalls.
Luckily, the worst fears of emergency responders were not realized.
The explosion sent shrapnel flying, piercing an enormous asphalt tank, which caused the fire. But it missed a nearby tank storing hydrogen fluoride, a highly toxic chemical compound used to make high-octane gasoline. Hydrogen fluoride can be fatal if it's inhaled.
The near-miss prompted calls from Larson and Superior Mayor Jim Paine for Husky to discontinue use of hydrogen fluoride.
On Monday, the Duluth City Council plans to vote on a resolution asking the federal Environmental Protection Agency to study the use of hydrogen fluoride in refineries to ensure the safety of communities like Duluth and Superior.
Larson, who backs the resolution, said the explosion at the Husky refinery was a call to action.
Husky officials in April said they planned to continue to use the substance when they rebuild the facility, after an analysis concluded that "alternatives were not commercially viable or introduced significant risks for the Superior Refinery," according to Husky spokesperson Mel Duvall.
The company is incorporating additional safety measures as it rebuilds the refinery at a cost of more than $400 million, Duvall added.
Larson called Husky's decision to continue using hydrogen fluoride "unacceptable," although she acknowledged she does not have the power to stop the company from moving ahead with its plans.
"[But] I do have a way to help impact whether or not the industry is going to continue to be supported in making that choice," she said.
Larson isn't alone in asking the EPA to study the use of the chemical compound at refineries.
The U.S. Chemical Safety Board, the agency that probed the Husky refinery explosion, wrote to the EPA in April, asking the agency to update its last analysis of the use of hydrogen fluoride, which was completed in 1993.
"People are afraid. They are afraid of this toxic chemical in their midst, afraid of the potential for it to be released," said Kristen Kulinowski, the interim executive authority of the safety board.
Industry and government, she added, "need to do everything that we can to ensure that people remain safe in the shadows of these dangerous refineries."
She said the board's concern was further heightened last month after an explosion occurred in a Philadelphia refinery that also used hydrogen fluoride. Unlike the explosion in Superior, and an earlier explosion at a California refinery in 2015, the explosion in Philadelphia originated in the same alkylation unit where the HF is used.
"It remains a concern, that the next time one of these explosions happens in a refinery that uses HF, the community might not be so lucky," Kulinowksi said.
An EPA spokesperson said the agency is working on a response to the safety board's request.
Hydrogen fluoride is used in about a third of the nation's refineries, according to a report from the Center for Public Integrity, including at the Andeavor refinery in St. Paul Park, southeast of St. Paul.
Some Minnesota lawmakers have called on that refinery to also discontinue using the chemical.
Paine, the Superior mayor, said he supports the resolution Duluth will consider on Monday, adding that he plans to make the same request to the EPA. He said he wants Husky to build the safest refinery possible.
"The refinery still remains an important part of the economy in the city of Superior, and a lot of us over here very much support its operation," he said. "Safety is our first priority, but we still support an operating refinery as well."