California Code of Regulations
Title 8 - Industrial Relations
Division 1 - Department of Industrial Relations
Chapter 4 - Division of Industrial Safety
Subchapter 7 - General Industry Safety Orders
Group 18 - Explosive Materials
Article 114 - Storage of Explosive Materials
Section 5258 - Storage of Explosive Materials Underground

(a) Explosive materials stored underground shall be so located that should they detonate or burn, the escape route for the employees will not be obstructed.

(b) Magazines shall be at least 200 feet from active underground workings, 50 feet from other magazines and at least 25 feet of solid ground separation from any haulageway used for any purpose other than the transportation of explosive materials. Any timbers within 25 feet of any magazine shall be made fire resistant.

(c) Explosive materials shall not be stored in an underground work area during tunneling and construction operations.

(d) In magazines where explosive materials may become damp, electricity may be installed for drying purposes. Electrical equipment used shall comply with Class II, Division I, Hazardous Locations, Electrical Safety Orders. Electrical wiring shall be kept at least 5 feet from explosive materials. No other electrical wiring shall be permitted within 5 feet of any magazine.

(e) Underground storage magazines shall be conspicuously marked with the words, "EXPLOSIVES," in red letters at least 4 inches high and with 5/8 -inch stroke on a white background.

(f) Combustible rubbish shall not be permitted within 100 feet of any underground magazine.

(g) Detonator storage magazines shall be of the same construction as explosives storage magazines and shall be separated by at least 50 feet from other magazines.