225 ILCS 705/26.13

All hoisting shafts, air shafts, and escapement shafts constructed after March, 1910, shall be of fireproof construction, and if poured concrete is used in said construction it shall be not less than 6 inches in thickness. Cage guides and buntons may, however, be constructed of wood. Drifts and slopes must be fireproof for a distance of 300 feet from the entrance.