52 Pa. Stat. § 690-210
When mine workings become so extensive that the mine foreman is unable personally to carry out the requirements of this act pertaining to duties, the mine foreman shall have the right to employ a sufficient number of competent individuals to act as his assistants who shall be under his instruction and the operator's or the superintendent's instruction in carrying out the provisions of this act. In each mine the mine foreman's assistants must possess assistant mine foreman certificates. In case of the necessary temporary absence of the mine foreman, the mine foreman may deputize his responsibilities, for the time being, to an assistant mine foreman who shall perform all the duties of the mine foreman. Any mine foreman, assistant mine foreman, mine examiner or mine electrician may supervise and direct the work of a maximum of two noncertified miners and shall instruct the individuals how safely and properly to perform their work.
52 P.S. § 690-210