Chicago authorities said Tuesday that a man visiting his son at the Cook County Jail last weekend was accidentally trapped in an empty maximum security visiting area for 31 hours.

The Chicago Tribune identified the father as a middle-aged man, and reported that he was moved to an area in the jail that is not used during the weekends.

The room has a concrete door and is used for people who visit the jails super-maximum security inmates. His son is reportedly awaiting trial on a drug case.

"He encountered a door that was propped open and he went in and the door shut behind him," Cara Smith, the jail’s executive director, told the paper. The door was apparently left open by contractors working at the facility.

He was found Monday at 1 a.m. after he was able to break a sprinkler head, which set off an alarm. He required a few stitches on his thumb.

"Anything like this is unacceptable," Smith said. The jail is investigating.