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Hazardous Materials Program Guidance: UST Overfill Prevention - Page 5 of 7 <br />G. Overfill Activation Height <br />If USTs were rectangular, calculating activation height would be a simple matter. To activate at 90% of <br />capacity, you would merely locate a point that is 90% of the distance between the tank floor and tank roof. <br />Since USTs are cylinders, this approach will not work. [Note: 1" of product at 50% of a cylindrical tank height <br />holds many more gallons than 1" of product at 90% since the tank is much wider in the middle. This is <br />compounded in the case of fiberglass tanks, which are cylinders with rounded ends, and thus are both wider <br />and longer in the center than they are near their tops and bottoms. Also, compartmented fiberglass tanks <br />will have a BASE TANK that has two convex ends and an END TANK that has one convex end and one concave <br />end.] It is necessary to consult the manufacturer's tank calibration chart to determine the height above the <br />tank bottom that corresponds to 90% of the liquid capacity. <br />BASE TANK END TANK <br />The following tables use data from the manufacturers' tank calibration charts and provide 90% and 95% <br />capacity data for several types of commonly encountered USTs. They are accurate to approximately ± 0.1, <br />intended merely for quick checks of contractor's calculations, and are NOT a substitute for the contractor <br />performing their own calculations when installing or certifying equipment. <br />Data for only a few of the more common tanks are included. If the tank you are dealing with is not on one <br />oI these charts, you need to obtain the UST manufacturer's tank calibration chart. Multiply the tank's actual <br />capacity by 0.9 or 0.95 to determine the number of gallons that equals 90% or 95% of tank capacity, then <br />find the number of inches on the tank chart that corresponds to that number of gallons. <br />Containment Solutions Double -Wall Stand -Alone USTs: <br />Size Diameter Actual Actual <br />(Gallons) <br />(Feet) <br />Capacity <br />(Gallons) <br />Diameter <br />(Inches) <br />90%Volume <br />(Gallons) <br />90% Height <br />(Inches) <br />95% Volume <br />(Gallons) <br />95% Height <br />(Inches) <br />41000 <br />8 <br />31998 <br />91.625 <br />31598 <br />76.1 <br />31798 <br />81.8 <br />61000 <br />8 <br />51897 <br />91.625 <br />51307 <br />76.5 <br />51602 <br />82.1 <br />81000 <br />8 <br />71796 <br />91.625 <br />71016 <br />76.7 <br />7,406 <br />82.3 <br />12,000 <br />8 <br />11,595 <br />91.625 <br />10,436 <br />76.9 <br />11,015 <br />83.5 <br />15,000 <br />8 <br />14,545 <br />91.625 <br />13,091 <br />76.9 <br />13,818 <br />82.5 <br />10,000 <br />10 <br />10,257 <br />119.625 <br />91231 <br />99.2 <br />91744 <br />106.4 <br />12,000 <br />10 <br />11,873 <br />119.625 <br />10,686 <br />99.4 <br />11,279 <br />106.7 <br />15,000 <br />10 <br />15,104 <br />119.625 <br />13,594 <br />99.7 <br />14,349 <br />107.0 <br />20,000 <br />10 <br />19,951 <br />119.625 <br />17,956 <br />100.0 <br />18,953 <br />107.3 <br />25,000 <br />10 <br />24,970 <br />119.625 <br />22,473 <br />100.2 <br />23,722 <br />107.4 <br />30,000 <br />10 <br />29,816 <br />119.625 <br />26,834 <br />100.3 <br />28,325 <br />107.5 <br />40,000 <br />10 <br />39,854 <br />119.625 <br />35,869 <br />100.2 <br />37,861 <br />107.6 <br />HMPG-025 5/7 -Rev. 09/20/18 <br />