All blasting powder, or other high explosive, in excess of the temporary supply required in such mine as designated in section 293.270, shall be stored in a magazine, placed not less than three hundred feet distant from any shaft, habitation, public highway, public railway, or from the boundary line of any mining property; provided, however, that in cases where the location of any mining property makes it impossible to comply with the provisions of this section, the director of the division of mine inspection may grant permission, in writing, to the operator of such mining property, or such operator’s agent, to place such magazine in some other place on such mining property, if, in the opinion of such director, such location shall not be dangerous to the safety of those employed within such mine; and provided further, that every magazine, where powder or other high explosive is stored, as provided in this section, shall be ventilated.