Document R28DV9mMROGByL63nx82ZjNV

Smaller-capacity units (e.g., 1,000 ftVmin) equipped with appropriately sized fans and filters may be used to ventilate smaller work areas. The desired air flow could be achieved with several units. F.2.1.2.2 Filters the final filter must be the HEPA type. Each filter should have a standard nominal rating of at least 1,100 ftVmin with a maximum pressure drop of 1 inch H2O clean resistance. The filter media (folded into closely pleated panels) must be completely sealed on all edges with a structurally rigid frame and cross-braced as required. The exact dimensions of the filter should correspond with the dimensions of the filter housing inside the cabinet or the dimensions of the filter-holding frame. The recommended standard size HEPA filter is 24 inches high x 24 inches wide x 11 -1/2 inches deep. The overall dimensions and squareness should be within 1/8 inch. A continuous rubber gasket must be located between the filter and the filter housing to form a tight seal. The gasket material should be 1 /4 inch thick and 3/4 inch wide. Each filter should be individually tested and certified by the manufacturer to have an efficiency of not less than 99.97 percent when challenged with 0.3-j/m dioctylphthalate (DOP) particles. Testing should be in accordance with Military Standard Number 282 and Army Instruction Manual 136-300-175A. Each filter should bear a UL586 label to indicate ability to . perform under,specified conditions. Each filter should be marked with: the name of the manufacturer, serial number, air flow rating, efficiency and resistance, and the direction of test air flow. Prefitters, which protect the final filter by removing the larger particles, are recommended to prolong the operating life of the HEPA filter. Prefilters prevent the premature loading of the HEPA filter. They can also save energy and cost. One (minimum) or two (preferred) stages of . .prefiltration may be used. The first-stage prefilter should be a low-efficiency type (e.g., for particles 10 /rm and larger). The second-stage (or intermediate) filter should have a medium ^ efficiency (e.g., effective for particles down to 5 /am). Various types of filters and filter media for prefiltration applications are available from many manufacturers. Prefilters and inter mediate filters should be installed either on or in the intake grid of the unit and held in place with special housings or clamps. F.2.1.2.3 Instrumentation v- Each unit should be equipped with a Magnehelic gauge or manometer to measure the pressure drop across the filters and indicate.when filters have become loaded and need to.be changed. The static pressure across the filters (resistance) increases as they become loaded with duSt, affecting the ability of the unit to move air at its rated capacity. F.2.1.3 Electrical F.2.1.3.1 General The electrical system should have a remote fuse disconnect. The fan motor should be totally . enclosed, fan-cooled, and the nonoverioading type. The unit must use a standard 115-V, : . :F-3 GLEASON-001127