Fitchburg, WI – A boiler exploded at a minimum security prison Tuesday, injuring two maintenance workers and an inmate.

Oakhill Correctional Institution Warden Deirdre Morgan said the two workers and the inmate were trying to re-light a pilot light on the boiler in a basement room when it exploded at 8:45 a.m. Department of Corrections officials said the explosion involved natural gas.

The workers and the inmate suffered minor injuries that Morgan described as burns. They were taken to area emergency rooms.

The two workers were treated and released and given the afternoon off. Morgan declined to comment on the inmate’s status.

The explosion caused no structural damage, but prison officials evacuated about 200 inmates from a pair of housing units above the boiler room to the prison’s school and chapel as a precaution, Morgan said.

The prison’s perimeter was never compromised, and no inmate tried to escape during the evacuation, Morgan said.

Oakhill houses about 670 inmates.