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The city of Duluth is calling on a federal agency to investigate the use of hydrogen fluoride by oil refineries, more than a year after an explosion at a plant in neighboring Superior, Wis., sparked concerns about the toxic chemical.

The City Council voted unanimously Monday to pass a resolution requesting the Environmental Protection Agency (EPA) further study whether refineries should be able to use hydrogen fluoride “to ensure the safety of local communities, such as the Twin Ports.”

In April 2018, Superior officials evacuated the city after an explosion and fire at Husky Energy oil refinery, where hydrogen fluoride is dissolved in water and used as a catalyst to boost octane in gasoline.

Hydrogen fluoride is a fast-acting acid that causes burns and can kill. Accidents involving the chemical are rare but can be catastrophic if it leaks and forms a gas cloud. According to EPA records, a massive leak could put 180,000 people at risk in the Twin Ports.

The U.S. Chemical Safety Board, an independent agency, sent a letter to the EPA in April also encouraging it to review its study of hydrogen fluoride and refineries’ risk-management plans, which has not been done since 1993.

An EPA spokesperson said Friday that the agency is still working on a response to the board’s request.

Duluth council members and residents at Monday’s meeting pointed to alternatives to the chemical that could be safer. Husky Energy announced in April that it would continue to use hydrogen fluoride once its facility is rebuilt because other options were not commercially viable or increased risks for the Superior refinery.

Katie Galioto • 612-673-4478