Pennsylvania Statutes Title 52 P.S. Mines and Mining § 70-801. Safety holes to be not more than one hundred fifty feet apart

Every passageway used by persons in any mine and also roads used  1 for transportation of coal or other material shall be made of sufficient width to permit persons to pass moving cars with safety, but if found impracticable to make any passageway of sufficient width, then holes of ample dimensions, and not more than one hundred fifty feet apart, shall be made on one side of said passageway. The said passageway and safety holes shall be kept free from obstructions and shall be well drained; the roof and sides of the same shall be made secure.