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Vents for Underground Flammable Liquid Storage Tanks.
(a) Every underground storage tank containing flammable liquids at atmospheric pressure and having a capacity of more than 100 gallons, shall have a galvanized vent opening so located that the discharge point is outside of any building higher than the fill pipe. Vent pipes from tanks storing Class I, II flammable liquids, and for Class III flammable liquids in tanks containing heaters or hot wells shall be so located that the discharge point is outside of the building, higher than the fill pipe opening, and not less than 12 feet above the adjacent ground level. Vent pipes shall terminate in a weatherproof hood. Vent pipes two inches or less in nominal inside diameter shall not be obstructed by devices that will cause a back pressure exceeding working pressure of the tank, and outlets shall be three feet measured horizontally or vertically from any window or door opening or any other building opening and shall not be trapped under eaves or other obstructions. If the vent pipe is less than ten feet in length or greater than two inches in nominal inside diameter, the outlet shall be provided with an Underwriters' Laboratories, Inc. listed vacuum and pressure-relief device, or there shall be an approved flame arrester located in the vent line at the outlet. In no case shall the flame arrester be located more than 15 feet from the outlet end of the vent line, except any underground gasoline tank installed after the passage of this ordinance shall be piped and equipped for vapor recovery. The vent terminal shall be a minimum of 12 feet or higher above the adjacent ground level and in no case less than three feet higher than the transport truck or tank that will supply such tank. The size of the vent shall be in accordance with paragraph (d) of this section. The outlet shall be provided with an Underwriters' Laboratories, Inc. listed vacuum and pressure-relief device. In no case shall the static head, including the relief device pressure-imposed on the tank, be greater than the working pressure of the tank. The fill pipe shall be of the tight seal type and piped below the suction pipe or pump inlet. No manifolding of vents, syphons, equalizers or other connection to any other tank shall be permitted. Overflow protection shall be provided by piping an extension into the tank to enable the contents of the delivery hose and the vapor recovery hose to flow right back into the storage tank. A dry break adapter and lock-type cap shall be provided with every tank and the recovery hose shall be full sized to the tank truck. No gauging opening shall be permitted, and the fill pipe may be utilized as a gauging opening and shall be kept locked when said tank is not being filled or gauged.
(b) When wire screen is used as a flame arrester, it shall be of noncorrosive wire screen not less than 30 mesh per inch. The screens on such openings shall be at the outer end of vent pipe and so arranged that it can be removed for cleaning purposes.
(c) Where a pump is used with a tight seal fill, the vent shall not terminate on or above any roof.
(d) Vent openings and vent pipes for underground Class I, II and III flammable liquid tanks shall be of ample size to prevent pressure in the tank during filling but not smaller than the pipe size as specified below:
Capacity of Tank U.S.Gallons | Diameter of Vent, Iron Pipe Size (inches) |
500 or less | 1-1/4 |
501 to 3,000 | 1-1/2 |
3,001 to 10,000 | 2 |
10,001 to 20,000 | 2-1/2 |
20,001 to 35,000 | 3 |
35,001 to 50,000 | 4 |
Tanks over 50,000 gallons shall have, in addition to the four-inch vent required for the first 50,000 gallons, an additional vent or vents installed as required by the capacity in the above table.
(Prior code § 129.1-15)