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PEIIRP1200-12 4.2.4 Preparation. The procedures in this sec- 4.2.7 Test Equipment. Test equipment shall tion are general in nature and reflect the suggested include: vacuum Ievels and hold times for testing tank 0 a vacuum-generating device that can be used in secondary containment areas. Consult tank manu- a Class I, Division 1 area capable of pulling 15 facturer and authority having jurisdiction (AHJ) inches of mercury(Hg)vacuum; guidelines before performing these tests as their requirements may differ. • an automatic vacuum shutoff valve or vacuum regulator(The shutoff valve can be set to close at Determine if there is liquid present in the intersti- a predetermined safe level, preventing the pos- tial space. If liquid is found, determine if the fluid is water or product, and remove it to the extent _. i practicable. The hydrostatic pressure from a high water table imposes inward pressure on the outer wall of a UST. Applying a vacuum to the interstitial space of the tank creates additional pressure on the outer Y 1 wall. These combined forces can damage the secondary tank wall when there is a large defined space between the primary and secondary tanks. Consequently, to prevent damage to the tank, it iss � s important to observe the water table and associated recommended vacuum levels when testing. ' .r . Vent the primary tank to atmosphere during the FIGURE 4-3. The vacuum gauge and control valve used test. for tank interstitial testing. In some installations, the tank interstitial space may be vented to minimize the buildup of conden- sation.In these cases, seal off any vent lines to the tank interstitial space prior to testing. Determine the volume of the tank. This informa- tion is available from facility records or the auto- Z. matic tank gauge (ATG) readout. 4.2.5 Steel Tanks. Determine if the interstitial space is a"tight wrap" design or a "110%contain- ment" design. Tanks with a 110% containment design should use the latest version of Steel Tank Institute's (STI) Recommended Practice ROI2, f Recommended Practice for Interstitial Tightness a Testing of Existing Underground Double Wall Steel Tanks for testing. For tight wrap tanks, use the test method in this section. f i 4.2.6 Fiberglass Tanks. Determine if the inter- stitial space is a "tight wrap" design or a "110% ' containment" design. Either type of fiberglass tank may use this test, or the latest version of Fiber- _ JdOV glass Tank & Pipe Institute's, Field Test Protocol y for Testing the Annular Space of Installed Under- FIGURE 4-4. The plumber's plug provides a leak-tight ground Fiberglass Double and Triple-wall Tanks connection to draw a vacuum on the tank interstitial with Dry Annular Space, FT&PI 4101107, space. Qpei.org