Separate surface magazines shall be provided for storage of explosives, detonators and blasting heater elements. Surface magazines shall be constructed of incombustible materials, be reasonably bulletproof and with no metal or sparking material exposed inside the magazine. Surface magazines shall be provided with doors constructed of at least one-fourth inch steel plate lined with a two-inch thickness of wood or the equivalent, properly screened ventilators, and with no openings except for entrances and ventilation, and shall be kept locked securely when unattended. The area for a distance of at least twenty-five feet in all directions shall be kept free of materials of a combustible nature; suitable warning signs shall be erected, so located that a bullet passing directly through the face of the sign will not strike the magazine. The location of magazines shall be not less than two hundred feet from any mine openings, occupied buildings or public roads unless barricaded. If magazines are illuminated electrically, the lamps shall be of vapor-proof type, properly installed and wired, and smoking and open lights shall be prohibited in or near any magazine.