At least 24 people were exposed to an unknown substance Wednesday morning at the Ross Correctional Institution in Chillicothe.

State Highway Patrol Lt. Robert Sellers said shortly after 9 a.m. Wednesday that the guards and inmates began showing signs of a possible overdose. Paramedics responded and administered Narcan, a drug reversing the effects of opiates, to the victims.

Sellers said there is no threat to the public and an investigation is underway to identify the substance.

A hazardous materials team from Columbus is responding to assist in cleaning the cell block where the exposure occurred. About 300 additional doses of Narcan are available if needed.

Nurses, inmates and corrections officers were all among those exposed to the substance. The nature of the substance has not been determined.

The guards and prisoners are being taken to Adena Medical Center for treatment. The hospital said in a statement that 11 to 15 patients are currently being treated and assessed at the facility.

The statement also said the prison had alerted the hospital it would be receiving "numerous unresponsive" patients. The conditions of the patients were not immediately available but were expected to be available later Wednesday.

Other inmates in the cell block where the exposure occurred have been relocated temporarily to another area of the prison.

Route 104 is closed in the area of the prison while crews respond to the scene.

The Ross Correctional Institution houses more than 1,900 inmates and has a staff of nearly 500, according to the Ohio Department of Rehabilitation and Correction.

bbruner@dispatch.com

@bethany_bruner