225 ILCS 705/31.01

All active underground working places in a mine shall be ventilated by a current of air containing not less than 19.5% of oxygen, not more than 0.5% of carbon dioxide, and no harmful quantities of other noxious or poisonous gases. The volume and velocity of the current of air shall be sufficient to dilute so as to render harmless, and to carry away, flammable or harmful gases.