Butler Ambulance Service responded to a call for multiple people exposed to hydrofluoric acid at Cleveland-Cliffs, 1 Armco Drive, Lyndora, Thursday morning.

The call came in around 9 a.m. for seven people with acid inhalation. All were transported to Butler Memorial Hospital for treatment, according to Gene Troyan, director of operations at the ambulance service.

“We don’t know how it happened,” Troyan said of the gas exposure.

According to Patricia Persico, senior director of corporate communications for Cleveland-Cliffs, six contractors and one Cleveland-Cliffs employee were working on an abandoned hydrofluoric acid line at the Butler Works plant.

“Due to a minor contained leak, there was a scent of fumes,” she said. “As a precaution the contractors and employee were sent to Butler Memorial Hospital.”

The patients were evaluated and given preventative breathing treatments. All returned to work later in the day.