1、PD 6609:2007 Environmental cleanliness in enclosed spaces Guide to in situ high efficiency filter leak testing ICS 13.040.30 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW PUBLISHED DOCUMENTPublishing and copyright information The BSI copyright notice displayed in this docume
2、nt indicates when the document was last issued. BSI 2007 ISBN 978 0 580 54666 2 The following BSI references relate to the work on this standard: Committee reference LBI/30 Draft for comment 05/30123389 DC Publication history First published July 2000 Second edition published July 2007 Amendments is
3、sued since publication Amd. no. Date Text affected PD 6609:2007 BSI 2007 i PD 6609:2007 Contents Foreword ii 0 Introduction 1 1 Scope 1 2 Normative references 1 3 Requirements for testing 1 Annexes Annex A (informative) High efficiency filter specification table 6 Annex B (informative) In situ leak
4、test report 11 Bibliography 14 List of figures Figure 1 Diagram of an aerosol challenge to multiple filters via an air handling unit 2 Figure 2 Diagram of aerosol filter testing 4 Figure A.1 Filter dimensions 7 List of tables Table A.1 High efficiency filter specification 8 Table B.1 In situ leak te
5、st report sheet 12 Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 14, an inside back cover and a back cover.PD 6609:2007 ii BSI 2007 Foreword Publishing information This Published Document is published by BSI and came into effect on 31 July
6、2007. It was prepared by Technical Committee LBI/30, Cleanroom technology. A list of organizations represented on this committee can be obtained on request to its secretary. Supersession This Published Document supersedes PD 6609:2000, which is withdrawn. Relationship with other publications BS 5295
7、:1989 (all parts) has been replaced by BS EN ISO 14644 (all parts). However, the withdrawn BS 5295:1989 contained information about in situ high efficiency filter testing using an oil aerosol challenge and a photometer that is not given in BS EN ISO 14644 (all parts). That information, which has bee
8、n revised with respect to the new requirements in BS EN ISO 14644-3:2005, is published in this document. Presentational conventions The provisions in this standard are presented in roman (i.e. upright) type. Its recommendations are expressed in sentences in which the principal auxiliary verb is “sho
9、uld”. Commentary, explanation and general informative material is presented in smaller italic type, and does not constitute a normative element. Contractual and legal considerations This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its
10、 correct application. Compliance with a British Standard cannot confer immunity from legal obligations. BSI 2007 1 PD 6609:2007 0I n t r o d u c t i o n Where high efficiency filters are fitted, it is important to ensure that the filter and its housing and sealing device do not permit the ingress of
11、 particles into a cleanroom or clean zone. This is checked by challenging the filter with an aerosol of particles dispersed upstream of the filter and scanning over the downstream face, frame and gasket of the filter to ensure that there are no leaks that exceed a specified level of penetration. The
12、 object of the in situ leak test described in this document is to determine if the filter has been damaged between manufacture and installation, and during subsequent use. In situ testing with oil aerosols might not be acceptable for some cleanroom applications where airborne chemical contamination
13、needs to be controlled, as oil deposited on the filter will outgas. In such cases, an alternative method that uses inert particles and a particle counter can be used. This method is not discussed in this document but is described in B.6.3 of BS EN ISO 14644-3:2005. 1 Scope This Published Document pr
14、ovides information supplementary to the provisions of BS EN ISO 14644-3:2005. In particular, it gives recommendations and explanatory guidance for in situ leak testing of high efficiency filters using an oil aerosol challenge and photometer. It also provides guidance on the procurement of replacemen
15、t filters (Annex A) and information that might be required in a test report (Annex B). The guidance contained in this document is for the leak testing of high efficiency air filters that can be face scanned. The document does not provide information on other tests carried out on high efficiency filt
16、ers installed in cleanrooms, such as pressure differentials, air supply volumes, and airflow uniformity. 2 Normative references BS EN ISO 14644-3:2005, Cleanrooms and associated controlled environments Part 3: Test methods 3 Requirements for testing 3.1 Aerosol injection The filter integrity test re
17、lies on a homogeneous distribution of aerosol test challenge upstream and across the whole filter face. Homogeneous distribution is defined as a variation in concentration of less than 15% in time about the average measured value. The upstream aerosol challenge should be measured as close as possibl
18、e to the filter, and ideally not more than 50 mm from the upstream face. PD 6609:2007 2 BSI 2007 To ensure good mixing it is essential that the aerosol is injected correctly. For ducted systems, aerosol injection ports will normally be required. When injecting into long ducted systems with distribut
19、ion legs along the main duct (see Figure 1), good mixing will not occur unless the distance D is at least 15 duct diameters. However the correct use of distribution sparge pipes may allow injection as near as one metre from the filter face to achieve homogeneous distribution of the challenge aerosol
20、. The aerosol injection point or port should be of sufficient size to accept the entry of the challenge aerosol and achieve the required upstream concentration. In some cases, oil aerosol injection pumps may be required to overcome the pressure in positive pressure ducts. Where an aerosol challenge
21、is injected upstream of an air conditioning unit, the refrigeration, heating and humidification circuits should be switched off to avoid attenuation of the aerosol challenge. Any pre-filters between the injection point and the high efficiency filter(s) should be removed prior to test. The sample flo
22、w rate should always be maintained at the calibrated value of the sampling instrument being used. Where a filter is installed in a negative pressure extract duct and the photometer is unable to overcome the negative pressure in the duct then leaks will not be detected. To overcome this, the photomet
23、er may be used in a “differential sampling mode”, if possible, where the exhaust of the photometer is returned to the exhaust duct. Figure 1 Diagram of an aerosol challenge to multiple filters via an air handling unit Distance D - 15 to 20 duct Normal system filter flow rate Aerosol inject remove fo
24、r test - switch off for test Pre - filters Fan Air conditioning system Normal system filter flow rate Normal system filter flow rate Duct Normal system flow rate BSI 2007 3 PD 6609:2007 3.2 Aerosol challenge Each filter requires a homogeneous oil aerosol challenge upstream of the filter of between 2
25、0 mg/m 3and 80 mg/m 3( 4g/l) of air. This can be provided by means of a thermal generator or (a) Laskin nozzle(s). BS EN ISO 14644-3:2005 considers that the mass median particle diameter of the test aerosol should be between 0.5 4m and 0.7 4m with a geometric standard deviation of up to 1.7. This is
26、 a size distribution typical of that produced by a Laskin nozzle. However, it is known that the mass median diameter of particles produced by a thermal generator is likely to be below the size suggested in BS EN ISO 14644-3:2005, and closer to the most penetrating particle size (MPPS) of high effici
27、ency filters. It is therefore likely that more leaks will be found when a thermal generator is used, but this is not considered a disadvantage. The upstream aerosol concentration is the 100% challenge and the percentage penetration is the downstream concentration expressed as a percentage of the ups
28、tream concentration. The percentage leakage penetration L can be calculated (see Figure 2) as follows: where: Y is the largest measured leak in mg/m 3( 4g/l), and X is the average upstream challenge concentration in mg/m 3( 4g/l). Prolonged exposure of filters to the challenge aerosol should be avoi
29、ded. In the case of controlled environments that are served with multiple high efficiency filters, it is recommended that means be provided to challenge and test filters one at a time. Where such a provision is impractical, the upstream aerosol concentration may be reduced to a level agreed between
30、the customer and the supplier, provided the downstream concentration at the pass/fail level is within the sensitivity of the photometer. The upstream aerosol concentration should remain the same throughout the duration of the scan of each filter and should therefore be checked and recorded both at t
31、he start and upon completion of each filter scan. L 100Y X - =PD 6609:2007 4 BSI 2007 3.3 System scanning Systems that do not have the means of accessing the upstream concentration cannot be tested by the method described in this document. A sampling probe should be used that ensures that the veloci
32、ty of air being drawn into the opening of the probe is the same as the velocity of air coming from the filter face. This can be calculated in accordance with BS EN ISO 14644-3:2005 B.6.2.4. A variation in velocity of up to 20% is acceptable. The filter should be scanned at a distance of approximatel
33、y 30 mm from the filter face using overlapping scans. NOTE BS EN ISO 14644-3:2005 B.6.2.7 states that “designated leaks are deemed to have occurred where there is a reading greater than 10 -4(0.01%) of the upstream challenge aerosol concentration”, but that “alternative acceptance criteria may be ag
34、reed between the customer and the supplier”. BS EN ISO 14644-3:2005 B.6.1.2b) states that an aerosol photometer can be used for MPPS penetrations equal to or greater than 0.003%. It has been well established that the use of linear photometers can readily measure aerosol penetrations down to 0.001%.
35、The sealing device, housing and filter are all subject to the in situ test. Scans should therefore be made around the gasket seal, along the joints of the filter frame, along the bond between the filter pack and the frame, and over the whole area of the filter face. Figure 2 Diagram of aerosol filte
36、r testing Homogenous aerosol distribution Filter Filter scanned with overlapping sweeps up to 30 mm from filter face 15 to 20 Duct from filter Air flow Point of injectiong/l X g/l Y BSI 2007 5 PD 6609:2007 A slow scanning velocity may improve sensitivity for finding leaks, and a fast scanning veloci
37、ty may fail to find leaks. The filter should therefore be scanned at a velocity v (in cm/s) in accordance with the formula given in BS EN ISO 14644-3:2005 B.6.2.5, namely: where W pis the probe dimension at right angles to the scan direction. 3.4 Airflow through filters Filter penetration varies wit
38、h flow rate through the filter. If the airflow through the installed filter is higher than the airflow at which it was tested by the manufacturer, the filter penetration may increase above that to which the filter was manufactured, to a point where it gives an in situ test failure. 3.5 Repair of fil
39、ters BS EN ISO 14644-3:2005 B.6.6 says that “leakage repair should only be acceptable by agreement between the customer and the supplier”. It should be noted that an effective repair at the gasket, and between the filter pack and frame, can often be achieved, but the repair of media leaks is difficu
40、lt to achieve and, because of blockage, may have adverse effects on the uniformity of airflow. In a non-unidirectional cleanroom the air supply will quickly mix with room air and a less than perfect repair can be tolerated. However, in unidirectional flow, especially if the air is supplied directly
41、to a critical area, the filter would normally be renewed. Where temporary repairs are made for expediency, e.g. to allow vital work to continue, a replacement filter needs to be installed at the earliest possible opportunity. v 15 W p - =PD 6609:2007 6 BSI 2007 Annex A (informative) High efficiency
42、filter specification table A.1 High efficiency filter specification checklist It is important when changing filters to choose the correct replacement filter, as failure to do this could affect the ability of the filter to pass the in situ leak test and could also affect the overall performance of th
43、e system to which the filter is fitted. Unambiguous specifications in relation to the following aspects should be clearly stated on all requisitions or orders to ensure compatibility with application and to avoid inappropriate filters being supplied: a) application and orientation; b) volumetric flo
44、w rate, uniformity of airflow and “clean” pressure drop; c) pass/fail criteria for leakage and penetration with reference to the in situ test method to be used; d) pass/fail criteria for leakage and penetration with reference to manufacturers tests (A.2); e) sealing arrangement; f) size and form of
45、construction. When specifying the size of a standard type of filter, it is a commonly accepted practice to quote “height by width by depth”. The convention for filters is for height and width to define the dimensions of the face area of the filter, where the pleats are in the vertical or “height” di
46、rection, and for depth to define the dimension in the direction of airflow, as illustrated in Figure A.1. Failure to observe this system can result in a filter of inappropriate dimensions being supplied. Table A.1 is a suggested high efficiency filter specification checklist. This can also be used a
47、s the basis for the manufacturers certificate of conformance where required. BSI 2007 7 PD 6609:2007 A.2 Manufacturers high efficiency filter tests Eurovent 4/4 (BS 3928:1969) specifies a volumetric test method commonly used by filter manufacturers for testing high efficiency filters. The Eurovent 4
48、/4 test method uses an aerosol of sodium chloride with a relatively large mass median diameter of 0.7 4m. The Eurovent 4/4 test measures overall efficiency only and is not a scan test. Therefore a Eurovent 4/4 filter for use in a cleanroom should be subject to an additional scan test by the filter m
49、anufacturer, using a method similar to that used for the in situ test, to ensure that local penetrations are within specified limits. BS EN 1822 (all parts) is a manufacturers standard for the classification and testing of high efficiency air filters. Filters are classified in terms of overall and local efficiency at the most penetrating particle size (MPPS). Figure A.1 Filter dimensions Depth Width Height Airflow directionPD 6609:2007 8 BSI 2007 Filters tested to BS EN 1822 may have a suitable overall effi
