UPDATE 8/30/18 @ 3:22 a.m.

A combination of heroin and fentanyl has been identified as the substance that caused 29 people to be treated for overdose symptoms at the Ross Correctional Institution.

One inmate and one staff member are still in the hospital after the exposure, according to the Ohio State Highway Patrol.

Most of the victims' symptoms included sweating and light-headedness. They were administered Narcan, the drug that reverses an overdose.

A spokesperson for Adena Regional Medical Center said more than 100 people were available to help during the event. Adena took full precautions with its staff to avoid exposure, the spokesperson said. The victims received decontamination showers before they were moved from the emergency room.

At Ross Correctional Institution, 31 inmates who were not affected were removed from the cellblock and are located in other secure areas of the facility, the Ohio State Highway Patrol says. That agency also reports additional Narcan is on hand at the prison as a precaution.

UPDATE 8/29/18 @ 4:35 p.m.

A medical doctor has confirmed the powerful drug fentanyl was responsible for the exposure to 29 people at the Ross Correctional Institution.

As of Wednesday afternoon, the prison is still in code yellow alert. The doctor describe it as a "once in a lifetime event." Twenty-three of those affected were correction officers. Four nurses and one inmate also were exposed. All of those victims were taken to Adena Regional Medical Center. Another inmate was treated at the scene and not transported.

None of the people exposed to the fentanyl, which is 50 to 100 times more potent than heroin, fell extremely ill, a spokesperson for Adena Regional Medical Center said. Only one person, the inmate, was admitted and will have to stay at the hospital overnight. He was unresponsive and not breathing before he was stabilized.

Most of the victims' symptoms included sweating and light-headedness. They were administered Narcan, the drug that reverses an overdose.

The hospital spokesperson said more than 100 people were available to help at Adena during the event. Adena took full precautions with its staff to avoid exposure, the spokesperson said. The victims received decontamination showers before they were moved from the emergency room.

At Ross Correctional Institution, 31 inmates who were not affected were removed from the cellblock and are located in other secure areas of the facility, the Ohio State Highway Patrol says. That agency also reports additional Narcan is on hand at the prison as a precaution.

Keep checking WSAZ Mobile and WSAZ.com for the latest information.

UPDATE 8/29/18 @ 11:41 a.m.

Twenty-four people, including correctional officers, nurses and inmates, have been exposed to what investigators believe is fentanyl at the Ross Correctional Institution.

Fentanyl is a powerful and dangerous drug. It is 50 to 100 times more potent than heroin according to the Centers for Disease Control.

The Ohio State Highway Patrol is investigating the incident that is drawing a major emergency response at the prison.

No deaths have been reported.

All of those affected were taken to Adena Regional Medical Center.

Troopers say several doses of Narcan - the drug that reverses an overdose - have been given to victims and there are an additional 300 doses available at the prison.

Investigators say they have cleared the contaminated cell block. Anyone who was in that area has been temporarily relocated within the facility.

A hazardous material decontamination team is on the way.

We have a crew heading to the scene.

Keep checking WSAZ Mobile and WSAZ.com for the latest information.

UPDATE 8/29/18 @ 10:45 a.m.

A major emergency response has been reported at Ross Correctional Institution after several staff members were sickened by an unknown substance, WCMH out of Columbus reports.

According to the Ohio State Highway Patrol, 15 guards, five nurses and one inmate were sickened by an unknown substance, Wednesday morning at the Ross Correctional Institution.

They are being treated as possible drug overdoses, according to troopers.

Investigators are still working to determine what the substance was, but extra doses of narcan were brought to the prison.

Troopers say the drug was possibly fentanyl.

Chillicothe Police have confirmed they have responded to the scene to assist with the situation.

There is no threat to the public, according to troopers.

NBC4 has several crews headed to the scene to gather more information.

The Ross Correctional Institution is a medium security prison for men that can house about 2,000 inmates. It has 494 staff members and located along S.R. 104 in Chillicothe.

ORIGINAL STORY 8/29/18

The Ross County Jail is currently on lockdown.

The Ohio State Highway Patrol confirms the facility is on lockdown Wednesday morning.

Troopers could not confirm why this is happening or what type of incident occurred.

We are told investigators will release more information later in the morning.

We have a crew heading to the scene.

Keep checking WSAZ Mobile and WSAZ.com for the latest information.