A suitable number of fire hydrants shall be located at a distance of not more than 500 feet from the holder shell to insure an adequate supply of water in case of fire, excepting in the outlying territory where no water supply is available and/or where there are no buildings within 300 feet of the holder. No permanent buildings shall be erected on company property within 100 feet of a holder shell, except buildings of fire resisting construction and no gas, oil or other highly inflammable material (except lubricating oil) shall be stored therein. All gasoline tanks for use of company vehicles shall be placed underground; no temporary structures shall be erected at a radial distance of less than 50 feet from the holder shell; no combustible material of any kind shall be stored in a temporary structure of wood or other inflammable material.