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ASTM F91-06(R2019) pdf free download

ASTM F91-06(R2019) pdf free download.Standard Practice for Testing for Leaks in the Filters Associated With Laminar Flow Clean Rooms and Clean Work Stations by Use of a Condensation Nuclei Detector
1. Scope
1.1 This practice covers the testing of the integrity of high-efficiency particulate air (HEPA) filters installed in lami- nar flow clean rooms ofthe ceiling to floor or wall to wall type, and laminar flow clean work stations. The recommended practice may be used to detect faults or voids in the filter media itself or in the joints between the filter and the room or work station structure. The determination of filter media efficiency is not within the scope of this practice. 1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.2.1 Exception—The values given in parentheses in inch- pound units are for information only. 1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.4 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Terminology
2.1 Definitions: 2.1.1 condensation nuclei—particles within the size range from 0.001 to 0.1-µm radius. 2.1.2 HEPA filter—high-efficiency particulate air filter. 2.1.3 laminar flow—airflow in which the air confined within the walls of a room or a smaller work station moves as an isovelocity front along parallel flow lines. 2.1.4 leak—a gap or void in the filter media, or in the associated gaskets, which permits unfiltered room air to pen- etrate the clean room or clean work station.
3. Summary of Practice
3.1 This recommended practice takes advantage of the fact that a HEPAfilter retains a high percentage ofthe condensation nuclei found in ordinary room air. In this recommended practice a nuclei counting apparatus is arranged to sample small areas at the filter surface and the joints at the filter edges. The HEPA filter effluent normally shows a low nuclei count (<100 particles/cm 3 ). When a leaking filter area is encountered, an increase of at least ten-fold in the particle count is noticed within the 2-s response time of the nuclei counter.
5. Preparation for Test
5.1 Assemble the apparatus by slipping one end of the plastic hose over the funnel stem, and the other end over the nuclei counter input nipple. 5.2 Turn on the electrical supply to the nuclei counter and allow 30 min warm up time with the input tube sampling the effluent from a HEPA filter. 5.3 Measure the nuclei concentration at the intake to the HEPA filter. A concentration of less than 1000 particles/cm indicates a concentration insufficient for conveniently detecting leaks in the filter or its gaskets. 5.3.1 In the event that a nuclei concentration of less than 1000 particles/cm 3 occurs when sampling a clean work station, move the work station into a room having a less clean ambient such as a room not supplied with filtered air. 5.3.2 In the event that the intake nuclei concentration ofless than 1000 particles/cm 3 occurs in a laminar flow room of the ceiling to floor or wall to wall type, make the filter leak test at a time when the room is operating on a full work schedule with the maximum number of occupants. 5.3.3 Should the nuclei concentration level of the input air fail to reach 1000 nuclei/cm 3 after executing steps 5.3.1 or 5.3.2, set up a nuclei generator using a DPST relay (see 4.4). Wire one side of the relay so that in the at-rest condition current flows through the relay field coil, drawing the armature toward the field coil pole piece. This wiring arrange- ment should provide for the flow ofcurrent to be broken by this action of the armature, resulting in its springing back into its original position. The resulting cyclic or buzzer-like action of the relay will generate a large number of nuclei at the arcing contacts which can be used to increase the number of nuclei at the HEPA filter input. In the event that an insufficient number of nuclei are still counted at the filter input, increase the arc nuclei concentration by employing the unused set of contacts on the relay to make and break the secondary circuit of a variable transformer, adjusting to provide moderate visible arcing.

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