1、Designation: F 91 06Standard Practice forTesting for Leaks in the Filters Associated With LaminarFlow Clean Rooms and Clean Work Stations by Use of aCondensation Nuclei Detector1This standard is issued under the fixed designation F 91; the number immediately following the designation indicates the y
2、ear of originaladoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscriptepsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers the testing of the integrity of
3、high-efficiency particulate air (HEPA) filters installed in lami-nar flow clean rooms of the ceiling to floor or wall to wall type,and laminar flow clean work stations. The recommendedpractice may be used to detect faults or voids in the filter mediaitself or in the joints between the filter and the
4、 room or workstation structure. The determination of filter media efficiency isnot within the scope of this practice.1.2 The values stated in metric units are to be regarded asthe standard. The values given in parentheses in inch-poundunits are for information only.1.3 This standard does not purport
5、 to address all of thesafety concerns associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety andhealth practices and determine the applicability of regulatorylimitations prior to use.2. Terminology2.1 Definitions:2.1.1 condensation nucleiparticl
6、es within the size rangefrom 0.001 to 0.1-m radius.2.1.2 HEPA filterhigh-efficiency particulate air filter.2.1.3 laminar flowairflow in which the air confined withinthe walls of a room or a smaller work station moves as anisovelocity front along parallel flow lines.2.1.4 leaka gap or void in the fil
7、ter media, or in theassociated gaskets, which permits unfiltered room air to pen-etrate the clean room or clean work station.3. Summary of Practice3.1 This recommended practice takes advantage of the factthat a HEPAfilter retains a high percentage of the condensationnuclei found in ordinary room air
8、. In this recommendedpractice a nuclei counting apparatus is arranged to samplesmall areas at the filter surface and the joints at the filter edges.The HEPA filter effluent normally shows a low nuclei count(100 particles/cm3). When a leaking filter area is encountered,an increase of at least ten-fol
9、d in the particle count is noticedwithin the 2-s response time of the nuclei counter.4. Apparatus4.1 Condensation Nuclei Counter2,3.4.2 Plastic Tubing4, 9.5 mm (38 in.) in outside diameter; 6.5mm (14 in.) in inside diameter; of suitable length, not to exceed1.5 m (5 ft).4.3 Glass Laboratory Funnel,
10、50 mm in outside diameter, 7mm in stem diameter, 80 mm over-all length.4.4 Double-Pole Single-Throw Relay, 115 V, 8 A.5. Preparation for Test5.1 Assemble the apparatus by slipping one end of theplastic hose over the funnel stem, and the other end over thenuclei counter input nipple.5.2 Turn on the e
11、lectrical supply to the nuclei counter andallow 30 min warm up time with the input tube sampling theeffluent from a HEPA filter.5.3 Measure the nuclei concentration at the intake to theHEPA filter. A concentration of less than 1000 particles/cm3indicates a concentration insufficient for conveniently
12、 detectingleaks in the filter or its gaskets.5.3.1 In the event that a nuclei concentration of less than1000 particles/cm3occurs when sampling a clean work station,move the work station into a room having a less clean ambientsuch as a room not supplied with filtered air.5.3.2 In the event that the i
13、ntake nuclei concentration of lessthan 1000 particles/cm3occurs in a laminar flow room of theceiling to floor or wall to wall type, make the filter leak test at1This practice is under the jurisdiction of ASTM Committee E21 on SpaceSimulation and Applications of Space Technology and is the direct res
14、ponsibility ofSubcommittee E21.05 on Contamination.Current edition approved Nov. 1, 2006. Published December 2006. Originallyapproved in 1968. Last previous edition approved in 2001 as F 91 70(2001)e1.2Rich, T. A., “A Continuous Recorder for Condensation Nuclei,” Geofisica Purae Applicata, Milano, V
15、ol 50 1961 III, pp 4652.3General Electric Co., Schenectady, NY, Model No. 112L482G1 has been foundsatisfatory.4Tygon tubing or equivalent has been found satisfactory for this purpose.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.a
16、time when the room is operating on a full work schedule withthe maximum number of occupants.5.3.3 Should the nuclei concentration level of the input airfail to reach 1000 nuclei/cm3after executing steps 5.3.1 or5.3.2, set up a nuclei generator using a DPST relay (see 4.4).5.3.3.1 Wire one side of th
17、e relay so that in the at-restcondition current flows through the relay field coil, drawing thearmature toward the field coil pole piece. This wiring arrange-ment should provide for the flow of current to be broken by thisaction of the armature, resulting in its springing back into itsoriginal posit
18、ion. The resulting cyclic or buzzer-like action ofthe relay will generate a large number of nuclei at the arcingcontacts which can be used to increase the number of nuclei atthe HEPA filter input. In the event that an insufficient numberof nuclei are still counted at the filter input, increase the a
19、rcnuclei concentration by employing the unused set of contactson the relay to make and break the secondary circuit of avariable transformer, adjusting to provide moderate visiblearcing.6. Procedure6.1 Sample the nuclei concentration of the effluent of theHEPA filter at the downstream face of the fil
20、ter.6.1.1 Operate the nuclei counter on the most sensitive scalepossible.6.1.2 Use the plastic sampling tube with the funnel tip toscan the entire downstream surface of the filter and thegasketed joints at the filter edges. Scan by traversing the filterface in straight sweeps from left to right and
21、then from right toleft shifting the line of travel of the probe tip by the diameterof the funnel after each pass.6.1.2.1 Maintain the rate of traverse of the sampling probebetween 2 and 4 in./s.6.1.2.2 Have an assistant to the person making the testobserve, at all times while the test is in progress
22、, the nucleiconcentration meter and quickly report any increase in concen-tration. Classify an increase of ten times, or more, above thebackground nuclei count (that is, from 30 nuclei to 300nuclei/cm3) as a leak.6.2 Reported increases in the nuclei level shall require thatthe test operator backtrac
23、k in his traverse procedure anddetermine the location of the leak.6.2.1 Remove the funnel from the plastic hose and samplewith the hose itself in order to pin-point the location of theleak.6.2.2 Mark the location of the leak on the filter protectinggrill using a grease pencil, and retest the filter
24、after suitableremedial action has been taken.7. Keywords7.1 filter testing; HEPA filter testing; HEPA filters; leaktesting; particle filtersASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this
25、standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years
26、 andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committe
27、e, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).F91062
