ST. CHARLES COUNTY, Mo. – HAZMAT crews are responding to the release of dangerous gas at a water treatment plant Friday afternoon in St. Charles County.

Officials tell FOX 2 that four people are hospitalized after the gas release. This includes three men and one woman. All are being treated for various conditions at a hospital.

HAZMAT crews were first requested to the water treatment plant, located in the 1600 block of South Highway 94, around noon. There was a release of hydrogen floride gas for an undisclosed amount of time. It’s unclear what led up to the gas release.

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The Cottleville Fire Chief describes the gas as very dangerous. That gas can irritate the eyes, nose, and respiratory tract, while also presenting some concerns for breathing.

As crews work to clear the situation, Highway 94 is closed from Highway D to Interstate 64.

This is a developing story. FOX 2 will update as more information becomes available.