Ohio Rev. Code § 1565.24: Miner working alone - unqualified miners.

No person shall work by himself as a miner in a coal mine without having produced satisfactory evidence to the mine foreman of such mine that he has worked at least one year with, or as, a practical coal miner. This section applies only to mines generating methane, other gas, or combustible matter.

No mine foreman of a coal mine shall permit anyone to mine coal in such mine until such person is qualified, unless he is accompanied by a competent coal miner.