WFAA-TV

Inmates were being watched in an exercise yard at 6 a.m. Tuesday.

MINERAL WELLS — A private prison facility in Palo Pinto County is on lockdown as authorities investigate an inmate disturbance that erupted Monday night.

The problem started when hundreds of inmates refused to leave the recreation yard at about 9:15 p.m. About two dozen of them protested a rule requiring them to wear shirts in the recreation yard on a steamy summer night.

Those inmates set small fires in trash cans, broke windows and threw rocks and trash at jailers.

A spokeswoman says two employees of the Mineral Wells Pre-Parole Transfer Facility were treated on site for minor injuries during the disturbance.

There were no reports of injuries to inmates.

About 400 inmates refused to leave the recreation yard and return to their cells.

The spokesman said it took about three-and-a-half hours and the use of "approved, non-lethal chemical agents" to bring the situation under control.

Some two dozen inmates identified as playing a role in the uprising will be charged with inciting a riot. They will be relocated to other corrections facilities.

About 30 officers from Mineral Wells and surrounding agencies set up a perimeter outside the prison's gates to secure the area.

Capt. Mike McAllester of the Mineral Wells Police Department said this has happened before. "This is one of several in the last few years, but most recently we had one last summer."

Corrections Corporation of America's of Nashville, Tennessee, owns and operates the all-male, minimum-security facility.

WFAA-TV reporter Cynthia Vega in Mineral Wells and the Associated Press contributed to this story.