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44 WISCONSIN ADMINISTRATIVE CODE Ind 8 1.The flow capacity of tank venting devices under 8 inches in nominal pipe size shall be determined by actual test of each type and size of vent. These flow tests may be conducted by the manufacturer if certified by a qualified impartial observer,or may be conducted by a qualified,impar- tial outside agency. The flow capacity of tank venting devices 8 inches nominal pipe size and larger,including manhole covers with long bolts or • equivalent,may be calculated provided that the opening pressure is ac- tually measured,the rating pressure and corresponding free orifice area • are stated, the word "calculated" appears on the nameplate, and the computation is based on a flow coefficient of 0.5 applied to the rated orifice area. • 2. A suitable formula for this calculation is: CFH= 1,667Cf.VPt— Pa where CFH=venting requirement in cubic feet of free air per hour Cf=0.5 [the flow coefficient] • A = the orifice area in sq. in. P• = the absolute pressure inside the tank in inches of water Pa = the absolute atmospheric pressure outside the tank in inches of water (7) [2-2.6] VENT PIPING FOR ABOVEGROUND TANKS. (a) [2-2.6.1] Vent piping shall be constructed in accordance with subch. 5. (b) [2-2.6.2] Where vent pipe outlets for tanks storing Class I liquids are adjacent to buildings or public ways.they shall be located so that the vapors are released at a safe point outside of buildings and not less than 12 feet above the adjacent ground level.In order to aid their dispersion, vapors shall be discharged upward or horizontally away from closely ad- jacent walls.Vent outlets shall he located so that flammable vapors will not be trapped by eaves or other obstructions and shall be at least 5 feet from building openings. (c) [2-2.6.3] The manifolding of tank vent piping shall be avoided except where required for special purposes such as vapor recovery,vapor conservation or air pollution control. When tank vent piping is mani- folded,pipe sizes shall be such as to discharge,within the pressure limi- tations of the system,the vapors they may be required to handle when manifolded tanks are subject to the same fire exposure. (d) [2-2.6.4] 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 pre- vent contamination and possible change in classification of the less vola- tile liquid. (8) ABOVEGROUND TANK OPENINGS OTHER THAN VENTS. (a) Connec- tions.Connections for all tank openings shall be vapor and liquid-tight. (b) External tank values. Each connection to an aboveground tank storing flammable or combustible liquids, located below normal liquid level,shall be provided with an external control valve located as close as practicable to the shell of the tank. Register,March, 1982,No.315 •