CALDWELL, Ohio (AP) – Officials say 29 inmates and four staff members have been treated for exposure to carbon monoxide at a medium-security state prison in southeastern Ohio.

The Marietta Times reports an assistant warden at Noble Correctional Institution says a malfunction in the air-handling system in one of the prison dormitories sickened inmates and staff Feb. 22.

Assistant Warden Joel Burris said the dormitory was evacuated and those who became ill were treated at hospitals and released the same day.

The prison has installed carbon monoxide detectors on both floors of the dormitory and plans to install them in all of the prison’s housing units.

Burris says contractors are trying to determine what caused the problem in a central heating system.