30 C.F.R. § 75.1312 – Explosives and detonators in underground magazines.

(a) The quantity of explosives kept underground shall not be more than is needed for 48 hours of use.
(b) Except as provided in § 75.1313, explosives and detonators taken underground shall be kept in—
1. (1) Separate, closed magazines at least 5 feet apart; or
2. (2) The same closed magazine when—
  1. (i) Separated by a hardwood partition at least 4 inches thick; or
  2. (ii) Separated by a laminated partition; or
  3. (iii) Separated by a device that is equivalent.
(c) Only explosives and detonators shall be kept in underground magazines.
(d) Magazines shall be substantially constructed and all interior surfaces shall be made of nonconductive material, with no metal or other conductive material exposed inside.
(e) All magazines shall be—
1. (1) Located at least 25 feet from roadways and any source of electric current;
2. (2) Located out of the direct line of the forces from blasting; and
3. (3) Kept as dry as practicable.
(f) Magazine locations shall be posted with indelibly marked and readily visible warnings indicating the presence of explosives.
(g) Only materials and equipment to be used in blasting shall be stored at magazine locations.