§ 14a.25. Vents for underground tanks.
(a) Vent pipes from underground storage tanks storing class I liquids shall be so located that the discharge point is outside of buildings, higher than the fill-pipe opening, and not less than 12 feet above the adjacent ground level. Vent pipes shall discharge only upward in order to disperse vapors. Vent pipes shall not be obstructed by devices provided for vapor recovery or other purposes unless the tank and associated piping and equipment are otherwise protected to limit back-pressure development to less than the maximum working pressure of the tank and equipment by the provision of pressure-vacuum vents, rupture discs, or other tank-venting devices installed in the tank-vent lines. Vent outlets and devices shall be protected to minimize the possibility of blockage from weather, dirt, or insect nests and shall be so located and directed that flammable vapors will not accumulate or travel to an unsafe location, enter building openings, or be trapped under eaves. Tanks containing class IA liquids shall be equipped with pressure and vacuum venting devices which shall be normally closed except when venting under pressure or vacuum conditions. Tanks storing class IB or class IC liquids shall be equipped with pressure-vacuum vents or with listed flame arresters. Tanks storing gasoline are exempt from the requirements for pressure and vacuum venting devices, except as required to prevent excessive back pressure, or flame arresters, provided the vent does not exceed 3 inches nominal inside diameter.
(b) Vent pipes from tanks storing class II or class III liquids shall terminate outside of building and higher than the fill-pipe opening. Vent outlets shall be above normal snow level. They may be fitted with return bends, coarse screens, or other devices to minimize ingress of foreign material. Vent piping shall be constructed in accordance with § 14a.51 (relating to scope and application).
(c) Tank-venting systems shall be provided with sufficient capacity to prevent blowback of vapor or liquid at the fill opening while the tank is being filled. Vent pipes shall not be less than 1¼ inch nominal inside diameter. The required venting capacity depends upon the filling or withdrawal rate, whichever is greater, and the vent-line length. Unrestricted vent piping sized in accordance with the following table will prevent back-pressure development in tanks from exceeding 2.5 psig Where tank venting devices are installed in vent lines, their flow capacities shall be determined in accordance with § 14a.8(b)(6) (relating to vents).
Maximum Flow
in GPMLength of Pipe—Vent
Lines of 50 feet, 100
feet, and 200 feet of pipe
plus 7 ells—(in feet)50 100 200 Vent Line Diameters
(in inches)100 1 1/4 1 1/4 1 1/4 200 1 1/4 1 1/4 1 1/4 300 1 1/4 1 1/4 1 1/2 400 1 1/4 1 1/2 2 500 1 1/2 1 1/2 2 600 1 1/2 2 2 700 2 2 2 800 2 2 3 900 2 2 3 1000 2 2 3 (d) Vent pipes shall be so laid as to drain toward the tank without sags or traps in which liquid can collect. They shall be located so that they will not be subjected to physical damage. The tank end of a vent pipe shall enter the tank through the top.
(e) When tank vent piping is manifolded, pipe sizes shall be such as to discharge, within the pressure limitations of the system, the vapors they can be required to handle when manifolded tanks are filled simultaneously; except that, for service stations, the capacity of manifolded vent piping shall be sufficient to discharge vapors generated when two manifolded tanks are simultaneously filled.
(f) Vent piping for tanks storing class I liquids shall not be manifolded with vent piping for tanks storing class II or class III liquids, unless positive means are provided to prevent the vapors from class I liquids from entering tanks storing class II or class III liquids, to prevent contamination and possible change in classification of the less volatile liquid.
(g) Where tanks are filled by the use of a pump through tight connections, a vent pipe not less in size than the discharge of the pump shall be used. Under no circumstances shall the vent pipe diameter be less than 1¼ inches nominal inside diameter.
(h) The design and location of vent pipe systems (except those designed for areas of mandatory vapor recovery) shall take into consideration the proximity of neighboring buildings with respect to flammable and noxious vapors.
Source The provisions of this § 13.25 amended through June 22, 1984, effective June 18, 1984, 14 Pa.B. 2131; transferred from 37 Pa. Code and renumbered as 34 Pa. Code § 14a.25, February 28, 2014, effective March 1, 2014, 44 Pa.B. 1233. Immediately preceding text appears at serial pages (259923) to (259925).
Cross References This section cited in 34 Pa. Code § 14a.21 (relating to location); 34 Pa. Code § 14a.141 (relating to scope and application); 34 Pa. Code § 14a.151 (relating to scope and application); and 34 Pa. Code § 14a.161 (relating to general provisions).
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