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(a) Vent pipes for enclosed storage tanks for fuel oil in connection with oil-burning equipment, and diesel oil in connection with emergency diesel-driven equipment shall be located so that the discharge point is outside of the building, and terminate in a weatherproof hood higher than the fill pipe opening. When such tanks contain heaters or hot wells, the opening of the vent pipe shall not be less than 12 feet above the adjacent ground level. Flame arresters shall be required for two and one-half inch and three inch vent pipes. Where a pump is used with a tight seal fill, the vent shall not terminate on or above any roof.
(b) Vent openings and vent pipes 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 25,000 | 3 |
Vents for Aboveground Flammable Liquid Tanks. Every aboveground flammable liquid tank shall have a vent opening for emergency and normal venting capacity not less than specified in Table 15-24-190(b).
A. Normal venting capacity requirements shall be obtained without exceeding the operating pressure or vacuum which may be applied regularly to a tank without causing physical damage or permanent deformation to the tank.
Inbreathing (vacuum relief) venting capacity requirement for maximum movement out of a tank shall be equivalent to 560 cubic feet of free air per hour for each 4,200 gallons per hour of maximum emptying rate, including gravity flow rate to other tanks, for flammable liquids of any flashpoint. Venting capacity requirement for thermal inbreathing for a given tank capacity for flammable liquids of any flashpoint shall be as shown in Column 2 of Table 15-24-190(a) of this section.
Outbreathing (pressure relief) venting capacity requirement for maximum flammable liquids movement into a tank and resulting evaporation:
(a) Class II and III flammable liquids shall be equivalent to 600 cubic feet of free air per hour for each 4,200 gallons per hour of maximum filling rate.
(b) Class I flammable liquids shall be equivalent to 1,200 cubic feet of free air per hour for each 4,200 gallons per hour of maximum filling rate.
Venting capacity requirement for thermal outbreathing, including thermal evaporation, for a given tank capacity:
(a) Class II and III flammable liquids shall be as shown in Column 3 of Table 15-24-190(a) and in no case shall be less than one and one-fourth inch nominal inside diameter.
(b) Class I flammable liquids shall be as shown in Column 4 of Table 15-24-190(a) and in no case shall be less than one and one-half inch nominal inside diameter. (See Table 15-24-190(a).)
B. Emergency Venting Capacity Requirements. Every aboveground storage tank shall have some form of construction or device that will relieve excessive internal pressure caused by exposure fires, as follows:
In a vertical tank the construction referred to above may take the form of a floating raft, lifter roof, or a weak roof-to-shell seam. The weak roof-to-shell seam (maximum three-sixteenths-inch single fillet weld) shall be constructed to fail preferential to any other seam. Where entire dependence for emergency relief is placed upon pressure-relieving devices, the total venting capacity of both normal and emergency vents shall not be enough to prevent rupture of the shell or bottom of the tank if vertical, or of the shell or heads if horizontal. The total capacity of both normal and emergency venting devices shall not be less than that derived from Table 15-24-190(b). Such device may be a self-closing manhole cover, or one using long bolts that may permit the cover to lift under internal pressure, or a self-closing gauge hatch, or an additional or large relief valve or pressure vacuum valve or valves, or an open vent. The wetted area of the tank shall be calculated on the basis of 55 percent of the total exposed area of a sphere or spheroid, 75 percent of the total exposed area of a horizontal tank and the first 30 feet above grade of the exposed shell area of a vertical tank.
Tank Capacity* | Inbreathing (Vacuum) All Stocks | Outbreathing (Pressure) | |||
(Barrels) | (Gallons) | Flashpoint 100° For Above | Flashpoint Below100°F | ||
Tank Capacity* | Inbreathing (Vacuum) All Stocks | Outbreathing (Pressure) | |||
(Barrels) | (Gallons) | Flashpoint 100° For Above | Flashpoint Below100°F | ||
1 | 2 | 3 | 4 | ||
60 | 2,500 | 60 | 40 | 60 | |
100 | 4,200 | 100 | 60 | 100 | |
500 | 21,000 | 500 | 300 | 500 | |
1,000 | 42,000 | 1,000 | 600 | 1,000 | |
2,000 | 84,000 | 2,000 | 1,200 | 2,000 | |
3,000 | 126,000 | 3,000 | 1,800 | 3,000 | |
4,000 | 168,000 | 4,000 | 2,400 | 4,000 | |
5,000 | 210,000 | 5,000 | 3,000 | 5,000 | |
10,000 | 420,000 | 10,000 | 6,000 | 10,000 | |
15,000 | 630,000 | 15,000 | 9,000 | 15,000 | |
20,000 | 840,000 | 20,000 | 12,000 | 20,000 | |
25,000 | 1,050,000 | 24,000 | 15,000 | 24,000 | |
30,000 | 28,000 | 17,000 | 28,000 | ||
35,000 | 31,000 | 19,000 | 31,000 | ||
40,000 | 34,000 | 21,000 | 34,000 | ||
45,000 | 37,000 | 23,000 | 37,000 | ||
50,000 | 40,000 | 24,000 | 40,000 | ||
60,000 | 44,000 | 27,000 | 44,000 | ||
70,000 | 48,000 | 29,000 | 48,000 | ||
80,000 | 52,000 | 31,000 | 52,000 | ||
90,000 | 56,000 | 34,000 | 56,000 | ||
100,000 | 60,000 | 36,000 | 60,000 | ||
120,000 | 68,000 | 41,000 | 68,000 | ||
140,000 | 75,000 | 45,000 | 75,000 | ||
160,000 | 82,000 | 50,000 | 82,000 | ||
180,000 | 90,000 | 54,000 | 90,000 | ||
* Interpolate for intermediate sizes. | |||||
Wetted Surface, Square Feet (a) | Venting Capacity Cubic Feet Per Hour | Minimum Opening, Iron Pipe Size, Inches (b) |
Wetted Surface, Square Feet (a) | Venting Capacity Cubic Feet Per Hour | Minimum Opening, Iron Pipe Size, Inches (b) |
20 | 21,000 | 2 |
30 | 31,600 | 2 |
40 | 42,100 | 3 |
50 | 52,700 | 3 |
60 | 63,200 | 3 |
70 | 73,700 | 4 |
80 | 84,200 | 4 |
90 | 94,800 | 4 |
100 | 105,000 | 4 |
120 | 126,000 | 6 |
140 | 147,000 | 6 |
160 | 168,000 | 6 |
180 | 190,000 | 6 |
200 | 211,000 | 6 |
250 | 239,000 | 6 |
300 | 265,000 | 6 |
350 | 288,000 | 8 |
400 | 312,000 | 8 |
500 | 354,000 | 8 |
600 | 392,000 | 8 |
700 | 428,000 | 8 |
800 | 462,000 | 8 |
900 | 493,000 | 8 |
1,000 | 524,000 | 10 |
1,200 | 557,000 | 10 |
1,400 | 587,000 | 10 |
1,600 | 614,000 | 10 |
1,800 | 639,000 | 10 |
2,000 | 662,000 | 10 |
2,400 | 704,000 | 10 |
2,800 and over | 742,000 | 10 |
(a) Interpolate for intermediate values.
(b) These pipe sizes apply only to open vent pipes of the indicated diameter not more than 12 inches long and a pressure in tank of not more than 2.5 pounds per square inch. If tank is to be equipped with venting device or flame arrester, the vent opening must accommodate the venting device or flame arrester sized in accordance with Column 2 of Table 15-24-190(b).
(Prior code § 129.1-16)