It shall be unlawful for any commission, board, county officer or other governing body of the state, or of any county, township, school district or city, to purchase or use any coal, except that mined or produced within the state by producers who are, at the time such coal is purchased and produced, complying with all the workers’ compensation and mining laws of the state. The provisions of this section shall not be applicable if coal produced within the state cannot be procured of a quantity or quality reasonably suited to the needs of such purchaser, nor if the equipment now installed is not reasonably adapted to the use of coal produced within the state, nor if the use of coal produced within the state would materially lessen the efficiency or increase the cost of operating such purchaser’s heating or power plant, nor to mines employing miners not now under the provisions of the workers’ compensation Act or who permit the miners to work in individual units in their own rooms.