Pennsylvania Statutes Title 52 P.S. Mines and Mining § 690-244. Underground storage of explosives

(a) Placement.--Explosives and detonators stored underground shall be:

(b) Separation.--If not kept in separate boxes or magazines not less than five feet apart, the explosives and detonators may be kept in the same box or magazine if separated by at least a four-inch hardwood partition or the equivalent. The boxes or magazines shall be kept at least 300 feet from the faces and out of the direct line of blasting and shall be installed outby the last permanent stopping and on intake air.