225 ILCS 705/31.05

If a split of air returning from active underground working places in a mine contains more than 1.0% of methane as determined by a permissible methane detector, a multi-gas detector, air analysis, or other recognized means of accurately detecting such gas, changes or adjustments shall be made at once in the ventilation in such mine so that such returning air shall not contain more than 1.0% of methane.