Nineteen people were hospitalized early Sunday after a chlorine gas leak at a suburban Chicago hotel hosting the annual Midwest FurFest convention, public safety officials said, Chicago Sun Times reported. Investigators believe the leak at the Hyatt Regency O'Hare in Rosemont, Illinois, was caused intentionally and are treating it as a criminal act. The Rosemont Public Safety Department evacuated the hotel, but guests were later allowed to return. The source of the leak appeared to be powdered chlorine found in a stairwell. Attendees at the convention dress as animals to celebrate art, literature and performance.