(225 ILCS 710/45.21) (from Ch. 96 1/2, par. 4274)
    Sec. 45.21. It shall be the duty of the operator to see that all miners in the mine are supplied at all times with such timbers as are necessary to keep their working places in a safe condition. For the purpose of this and the succeeding sections, the term "timbers" shall be held to include and mean all wood to be used by the miner, or all steel or concrete material used in lieu of timber.
(Source: Laws 1945, p. 1035.)