FITCHBURG, Wis. -- A natural gas explosion at a minimum security prison in Fitchburg injured two maintenance workers and an inmate Tuesday morning.

The Department of Corrections said the explosion occurred at 8:45 a.m. at Oakhill Correctional Institution in a boiler room near the food service area.

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State Department Of Corrections spokesman John Dipko said the three were performing maintenance on the boiler in a building adjacent to a housing unit and food service area and when they tried to restart it, it exploded.

The three were working on the pilot light and when they tried to re-start it, the boiler blew up.

The department said the three injured were sent to emergency rooms for treatment for non-life-threatening injuries.

The inmate and two staff members suffered minor burns when a boiler they were working on exploded.

The two staff members were treated and released from the hospital while the inmate remains hospitalized.

The department said housing units in the building where the explosion occurred were evacuated as a precaution. Officials said inmates were evacuated to empty spaces, including the chapel on campus.

The department said institution's perimeters were never compromised and neither was the safety of the community.

It's not clear at this point why the explosion occurred or the extent of the damage, WISC-TV reported. News crews are not being allowed into the correctional facility.

Two engineers from the Department of Administration are looking at the building but it doesn't appear there is any structural damage.

The inmates will remain on lockdown until the cleanup is complete.

Stay tuned to WISC-TV and Channel 3000 for continuing coverage.