225 ILCS 705/31.21

When the ventilating fan at any mine fails or stops, immediate action shall be taken to cut off the electric power and withdraw the workers from the face regions of the mine. In gassy mines if the ventilation is restored within a reasonable time, the face regions and other places where methane is likely to accumulate shall be re-examined by competent personnel, and if such region and places are found to be free from explosive gas the power may be restored and work resumed. If the ventilation is not restored within a reasonable time all underground employees shall be removed from the mine. In non-gassy mines if the ventilation is restored within a reasonable time the power may be turned on and work resumed without the necessity of re-examination.