225 ILCS 705/14.01

All buildings and structures erected, after the effective date of this Act, over a shaft, slope, or drift mouth within 100 feet of the opening shall be of metal, rock, clay, cement, clay or cement products, or any combination thereof. All fan houses, tops of air and escape shafts, and fan drifts, shall be constructed of the above materials, or a combination of them. Wood may be used only for floors, windows, doors and frames in the construction of such structures.