225 ILCS 705/31.06
If a split of air returning from active underground working places in a mine contains as much as 1.5% of methane as determined by a permissible methane detector, a multi-gas detector , air analysis, or other recognized means of accurately detecting such gas, the employees shall be withdrawn from the portion of the mine endangered thereby and all power shall be cut off from such portion of the mine until the quantity of methane in such split shall be less than 1.5%. However, in virgin territory in mines ventilated by exhaust fans, where methane is liberated in large amounts, if the quantity of air in a split ventilating the workings in such territory equals or exceeds twice the minimum volume of air prescribed in Section 31.02 and if only permissible electric equipment is used in such workings and the air in the split returning from such workings does not pass over trolley or other bare power wires, and if a certified person designated by the mine operator is continually testing the gas content of the air in such split during mining operations in such workings, it shall be necessary to withdraw the employees and cut off all power from the portion of the mine endangered by such methane only when the quantity thereof in the air returning from such workings exceeds 2%, as determined by a permissible methane detector, a multi-gas detector , air analysis, or other recognized means of accurately detecting such gas.
225 ILCS 705/31.06