293.520.  Experience required for miners, except trainees. — No person is permitted to engage in underground mining operations, except coal mining, for himself or for another unless he is to be employed by an operator as a trainee or to work under the supervision of an experienced miner for such length of time as will qualify said person to safely, for himself and others, perform underground work, or unless he offers satisfactory evidence that he has for one year worked in mines with or as a practical miner.