The Ohio State Highway Patrol said they were investigating a “substance exposure” that affected nearly 30 guards, inmates and nurses at a state correctional institution on Wednesday.

Ross Correctional Institution reported an inmate appeared to show signs of an overdose at 9:10 a.m., according to the OSHP. That person was given Narcan, an emergency medication administered to treat narcotic overdoses, and was transported to a hospital.

Emergency crews treated those who may have been exposed to the substance.

At least 28 people -- including 23 correctional officers, four nurses and one other inmate -- were potentially exposed to the substance at the correctional facility, officials said.

Police said in an earlier statement that "several doses of Narcan were administered to the victims, and an additional 300 Narcan doses are available at the facility."

All 28 affected persons were responsive and, with the exception of the inmate, transported to the Adena Regional Medical Center for evaluation, OSHP said in a statement.

Troopers told local media it was not immediately clear what the substance was, but it may have been fentanyl, WCMH-TV reported.

"Samples of the substance have been collected so it can be tested and identified," officials said.

The Ohio State Highway Patrol said the prison was secure and there was no danger to the public.

The contaminated cell block was cleared and about 31 inmates, who were not affected by the substance exposure, were relocated to other areas of the correctional facility.

They said a hazardous material team was at the cell block and performing cleaning procedures to decontaminate affected areas of the facility.

The Union-Scioto schools, which are near the correctional institution, were placed on a cautionary lockdown.

Fentanyl is a drug 50 times more potent than heroin and 100 times more potent than morphine, according to the Centers for Disease Control and Prevention.