Pennsylvania Statutes Title 52 P.S. Mines and Mining § 70-1121. Underground illumination

(a) In all mines the sockets of fixed electric lamps shall be of the so-called “weatherproof” type, the exterior of which shall be entirely nonmetallic. Flexible lamp cord connections are prohibited, except for portable lamps, as covered by rule subsection (c) of this section. Electric lights installed on all shaft and slope landings, hoist rooms, substations, pump rooms and the like, shall be on a separate circuit from the trolley circuit, and where A.C. current is used for lighting circuits, the maximum voltage shall be two hundred and twenty volts.

(b) Electric lamps shall be so placed that they cannot come in contact with combustible material.

(c) In gassy mines, portable electric lamps, other than battery lamps, shall not be used in connection with the repair and inspection of machines and equipment in face areas. When used elsewhere, they shall be protected by a heavy wire cage completely enclosing both lamp and socket, and shall be provided with a handle to which both cage and socket are firmly attached and through which the lead-in wires are carried.

(d) Electric lamps, when used in face areas of gassy mines, shall be installed in explosion proof enclosures.

(e) Electric lamps shall be replaced by a competent person only, and in face areas of gassy mines, after an examination for gas has been made with an approved safety lamp.

(f) In gassy mines, underground photography, using flash bulbs or other sources of artificial illumination shall be prohibited unless immediately preceded by an examination for gas by a qualified person and the place found safe.