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PE1/RP1200 -12 <br />4.2.4 Preparation. The procedures in this sec- <br />tion are general in nature and reflect the suggested <br />vacuum levels and hold times for testing tank <br />secondary containment areas. Consult tank manu- <br />facturer and authority having jurisdiction (A11.1) <br />guidelines before performing these tests as their <br />requirements may differ. <br />Determine if there is liquid present in the intersti- <br />tial space. If liquid is found, determine if the fluid <br />is water or product, and remove it to the extent <br />practicable. <br />The hydrostatic pressure from a high water table <br />imposes inward pressure on the outer wall of a <br />UST. Applying a vacuum to the interstitial space <br />of the tank creates additional pressure on the outer <br />wall. These combined forces can damage the <br />secondary tank wall when there is a large defined <br />space between the primary and secondary tanks. <br />Consequently, to prevent damage to the tank, it is <br />important to observe the water table and associated <br />recommended vacuum levels when testing. <br />Vent the primary tank to atmosphere during the <br />test. <br />In some installations, the tank interstitial space <br />may be vented to minimize the buildup of conden- <br />sation. In these cases, seal off any vent lines to the <br />tank interstitial space prior to testing. <br />Determine the volume of the tank. This informa- <br />tion is available from facility records or the auto- <br />matic tank gauge (ATG) readout. <br />4.2.5 Steel Tanks. Determine if the interstitial <br />space is a "tight wrap" design or a "110% contain- <br />ment" design. Tanks with a 110% containment <br />design should use the latest version of Steel Tank <br />Institute's (STI) Recommended Practice R012, <br />Recommended Practice for Interstitial Tightness <br />Testing of Existing Underground Double Wall Steel <br />Tanks for testing. <br />For tight wrap tanks, use the test method in this <br />section. <br />4.2.6 Fiberglass Tanks. Determine if the inter- <br />stitial space is a "tight wrap" design or a "110% <br />containment" design. Either type of fiberglass tank <br />may use this test, or the latest version of Fiber- <br />glass Tank & Pipe Institute's, Field Test Protocol <br />for Testing the Annular Space of Installed Under- <br />ground Fiberglass Double and Triple-wall Tanks <br />with Dry Annular Space, FT&PI 4/01/07 <br />0 pei.org <br />4.2.7 Test Equipment. Test equipment shall <br />include: <br />a vacuum-generating device that can be used in <br />a Class I, Division 1 area capable of pulling 15 <br />inches of mercury (Hg) vacuum; <br />an automatic vacuum shutoff valve or vacuum <br />regulator (The shutoff valve can be set to close at <br />a predetermined safe level, preventing the pos- <br />FIGURE 4-3. The vacuum gauge and control valve used <br />for tank interstitial testing. <br />FIGURE 4-4. The plumber's plug provides a leak-tight <br />connection to draw a vacuum on the tank interstitial <br />space.