Just read on HuffPo that fire was intentional:
"Authorities have found a man with "self-inflicted wounds" at an air traffic control center fire than has resulted in a complete ground-stop at Chicago and Detroit airports. Authorities believe the blaze was intentionally set, Aurora Police told WLS. It is not considered to be a terrorist attack. Two injured males were found in the building's basement, according to the Chicago Sun-Times. The main suspect had burns and self-inflicted wounds, according to ABC News. The second injured person's wounds are not self-inflicted, said the Sun-Times. Authorities have not made public the nature of the man's self-inflicted wounds, but did say both have been rushed to nearby hospitals, the Chicago Tribune reported. It is believed the unidentified man tried to commit suicide, officials told CNN. He is being questioned for his role in the incident."