Joint Committee Issue Paper

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Phillip Fowler
6 years ago
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NSF Standard(s) Impacted: Background: Provide a brief background statement indicating the cause and nature of concern, the impacts identified relevant to public health, public understanding, etc, and

1 NSF Standard(s) Impacted: Background: Provide a brief background statement indicating the cause and nature of concern, the impacts identified relevant to public health, public understanding, etc, and any other reason why the issue should be considered by the Committee. Reference as appropriate any specific section(s) of the standard(s) that are related to the issue. Currently NSF/ANSI 49 only allows HEPA/ULPA filter leak testing using an aerosol photometer and laskin nozzle aerosol generator. The European Standard for Biosafety cabinets (EN12469:2000) allows the use of either an aerosol photometer or discrete particle counter for filter testing. HEPA/ULPA filter leak testing with either an aerosol photometer or discrete particle counter have long been accepted in cleanroom testing as documented in ISO :2005 addressing Test Methods for Cleanrooms and associated controlled environments and IEST-RP-CC034.1 HEPA and ULPA Filter Leak Tests. Each method has its advantages and disadvantages, but both are commonly used in cleanroom and Biosafety cabinet applications globally. Adding the use of a discrete particle counter to the accepted methods for HEPA/ULPA filter leak testing for Class II biological safety cabinets in NSF/ANSI 49 would bring the standard into more alignment with other international standards. In addition, it could make the field certification of Biosafety cabinets less costly in regions where there are few BSCs or certification. Many of the companies or individuals servicing cleanrooms and clean air equipment already have a discrete particle counter to classify air cleanliness and to leak test filters in cleanrooms and other equipment. Requiring the purchase and maintenance of a costly piece of test equipment simply because NSF has not considered an accepted methodology hinders public safety by limiting the growth of proper field certification. Recommendation: Clearly state what action is needed: e.g., recommended changes to the standard(s) including the current text of the relevant section(s) indicating deletions by use of strike-out and additions by highlighting or underlining; e.g., reference of the issue to a Task Group for detailed consideration; etc. Using the recognized standards, for the consideration of the Joint Committee we have adapted the current language in Annex F to allow the use of a discrete particle counter to test HEPA/ULPA filters in a Class II BSC. F.5 HEPA/ULPA filter leak test (from NSF/ANSI ) F.5.1 Purpose This test determines the integrity of downflow and exhaust HEPA/ULPA filters, filter housings, and filter mounting frames. The cabinet shall be operated within ± 5 ft/min (0.025 m/s) of the nominal set point, with the exception of the downflow HEPA/ULPA filters on B1 cabinets. F.5.2 Apparatus

2 There are two approved methods for HEPA/ULPA filter leak testing; the aerosol photometer method and the discrete particle counter (DPC) method. The following devices may be used to carry out HEPA/ULPA filter leak testing: F For the aerosol photometer method, an aerosol photometer with linear or expanded logarithmic scale shall be used. The instrument shall be capable of indicating 100% upstream concentration with a minimum aerosol concentration of 10 μg/l of polydisperse dioctylphthalate (DOP) particles, or an equivalent fluid that provides the same particle size distribution (e.g., polyalpha olefin [PAO] di[2- ethylhexyl], sebecate, polyethylene glycol, and medicinal-grade light mineral oil)41 produced by the generator described in Annex A, section A or equivalent. It shall also be capable of detecting an aerosol concentration in the downstream equal to 10-5 of the upstream concentration of the same particles. The sampling rate of air shall be 1 ft3/min (5 x 10-4 m3/s) ± 10%. Probe area shall have a maximum open area of 1.7 in2 (11 cm2) and a minimum dimension of 0.50 in (1.3 cm). The photometer shall be set up in accordance with the photometer manufacturer's instructions or IEST-RP-CC-013 if instructions are not provided. F For the aerosol photometer method, an aerosol generator of the Laskin Nozzle type conforming to Annex A, figure A2 or equivalent shall be used to create an aerosol by flowing air through liquid DOP or equivalent substitute. When a Laskin nozzle generator is used, the compressed air supplied to the generator should be adjusted to a minimum of 20 psi (140 kpa), if using DOP or 23 psi (160 kpa) if using PAO, measured at the generator manufacturer s recommended location. The nozzles shall be covered with liquid to a depth not to exceed 1.25 in (31 mm). F For the aerosol photometer method, a pressure gauge for the generator having a maximum range of 0 to 80 psi (0 to 550 kpa) with resolution and accuracy of 1 psi (7 kpa) calibrated by the manufacturer or in accordance with the manufacturer's instructions shall be used. F For the DPC method, a discrete particle counter with the capability to detect particles 0.3 micrometers in diameter and greater and

3 compliant with ISO The discrete particle counter shall have an audible alarm that beeps for each particle that is counted and should have a counting mode that is continuous or at least as long as the time required to scan a filter. The sampling rate of air shall be 1 ft 3 /min (5 x 10-4 m3/s) ± 10%. Probe area shall have a maximum open area of 1.7 in 2 (11 cm 2 ) and a minimum dimension of 0.50 inches (1.3 cm). The particle counter shall be set up in accordance with the manufacturer's instructions. F For the DPC method, a suitable dilution system allowing the measurement of the upstream concentration. Given the challenge concentration specification of 12 to 24 million particles per ft 3 (420 to 840 million particles per cubic meter), this typically requires a dilution system of 1:100 or greater. F For the DPC method, a suitable challenge aerosol, detectable by the DPC and in the concentration 12 to 24 million particles per ft 3 (420 to 840 million particles per cubic meter) distributed uniformly upstream of the filter to be tested. F.5.3 Method of testing HEPA/ULPA filters F Filters that can be scanned with an aerosol photometer a) Turn on the cabinet blower and lights (types A1 and A2 and B2 downflow filter test). Remove the filter diffusers and protective covers if any are present. Place the generator so the aerosol is introduced into each cabinet fan upstream of the HEPA/ULPA filter(s). When the manufacturer has not identified the aerosol introduction point(s), introduce the aerosol in a manner to ensure thorough mixing in the cabinet airflow. For example, a T- connection can be fitted to the aerosol generator output to enable distribution of challenge into both entrances of a single blower or entrances of multiple blowers. The manufacturer shall determine the aerosol introduction point that provides the most uniform distribution. b) Turn on the photometer and adjust it in accordance with the manufacturer's instructions.

4 c) Determine the aerosol concentration upstream of the HEPA/ULPA filter. When the challenged airflow is not contaminated, sample the aerosol concentration upstream of the HEPA/ULPA filter. When the challenged airflow is contaminated or when measuring the upstream concentration is not practical, the upstream concentration can be calculated. For example, when DOP is used as the challenge aerosol with a Laskin nozzle aerosol generator at 20 psi (140 kpa), the following formula applies: μg/l = 13,500 x number of nozzles / ft3/min of challenged air NOTE Use of DOP substitutes will require modification of this formula, unless the photometer is calibrated with the substitutes to yield results equivalent to those of DOP. Use of DOP substitutes will also require pressures different from 20 psig. Use an aerosol concentration that is at least equal to the photometric equivalent of 10 μg/l of DOP. d) Set up the photometer to the upstream challenge in accordance with the photometer manufacturer's instructions to detect leaks greater than or equal to 0.01% of the upstream concentration. e) With the nozzle of the probe held not more than 1.0 in (2.5 cm) from the area being tested, scan the entire downstream side of the HEPA/ULPA filter(s) and the perimeter of each filter pack by passing the photometer probe in slightly overlapping strokes at a traverse rate of not more than 2 in/s (5 cm/s). Separate passes shall be made around the entire periphery of the filter, along the bond between the filter pack and frame, and around the seal between the filter and the device. f) Reported values shall be: upstream aerosol challenge concentration;

5 method used to report concentration (measured or calculated); maximum leak penetration in percent; method used (scanned or probe tested); and name of test (HEPA/ULPA filter leak test). F Filters that cannot be scanned with an aerosol photometer a) When a cabinet is ducted so that the exhaust filter cannot be scanned, it may be leak tested by drilling a hole approximately 0.3 inches (1 cm) in diameter in the duct at a downstream location that will produce a well-mixed aerosol and inserting the photometer sampling probe with rigid extension tubing through the hole. b) Reported values shall be: upstream aerosol challenge concentration; method used to report concentration (measured or calculated); maximum leak penetration in percent; method used (scanned or probe tested); and name of test (HEPA/ULPA filter leak test). F Filters that can be scanned with a discrete particle counter a) Turn on the cabinet blower and lights (types A1 and A2 and B2 downflow filter test). Remove the filter diffusers and protective covers if any are present. Place the generator so the aerosol is introduced into each cabinet fan upstream of the HEPA/ULPA filter(s). When the manufacturer has not identified the aerosol introduction point(s), introduce the aerosol in a manner to ensure thorough mixing in the cabinet airflow. For example, a T- connection can be fitted to the aerosol generator output to enable distribution of challenge into both entrances of a single blower or entrances of multiple blowers. The manufacturer shall determine the aerosol introduction point that provides the most uniform distribution.

6 b) Turn on the particle counter and adjust it in accordance with the manufacturer's instructions. c) Determine the particulate concentration upstream of the HEPA/ULPA filter. When the challenged airflow is not contaminated, sample the particle concentration upstream of the HEPA/ULPA filter using a suitable dilution system to verify a concentration of detectable particles. When the challenged airflow is contaminated or when measuring the upstream concentration is not practical, the upstream concentration can be calculated from a previous measurement of volumetric flow and particulate challenge concentration using the same generator and particle counter. For example, if C 1 (particles per ft 3 or m 3 ) was measured in a flow of Q 1 (cfm or m 3 /s), the concentration of C 2 in a flow of Q 2 (cfm or m 3 /s) can be calculated with the following formula: C 2 = C 1 Q 1 Q 2 Use a detectable particle concentration that is 12 to 24 million particles per ft 3 (420 to 840 million particles per cubic meter). NOTE: The DPC test parameters identified are derived from ISO Test Methods, Section B.6.3 Procedure for installed filter system leakage scan test with a DPC. S r C c P L 472 D p N p Note: 472 above from ISO represents the sample flow rate of 472 cm3/second or 1 cfm Using the formula for the scan rate above from ISO and IEST-RP-CC034 and inserting the recommended values specified for challenge concentration, probe width and scan rate, we can relate N p (the number of particles characterizing a leak while scanning) directly to the standard leak penetration and upstream challenge concentration.

7 S r = Scan rate shall be 2 inches/sec (5 cm/sec) C c = Challenge aerosol concentration upstream of filter in particles/cm 3 shall be 12 to 24 million particles per ft 3 (420 to 840 million particles per cubic meter) which yields a minimum concentration of 420 particles/cm 3 P L = standard leak penetration of filter to be tested. The leak criteria for the photometer test and for a BSC filter leak test using a particle counter as specified in EN12469 is 0.01% or D p = probe dimension parallel to the scan direction in cm. Our specification provides a minimum dimension of 0.5 in (1.3 cm). N p = expected number of particle counts which characterize the designated leak while scanning which shall be 5. S r C c P L 472 D p N p 5 cm/sec 420 particles/cm cm3/sec 1.3 cm 5 particles d) Set up the particle counter in accordance with the manufacturer's instructions to detect particles of the required size (0.3 micrometers) and larger. e) With the nozzle of the probe held not more than 1.0 inch (2.5 cm) from the area being tested, scan the entire downstream side of the HEPA/ULPA filter(s) and the perimeter of each filter pack by passing the photometer probe in slightly overlapping strokes at a traverse rate of not more than 2 inches/second (5 cm/s). Separate passes shall be made around the entire periphery of the filter, along the bond between the filter pack and frame, and around the seal between the filter and the device. In environments with a high background of airborne particles care must be taken to assure accurate results. A potential leak is identified by an observed particle count N p of 5 particles during the time the probe passes over the defect.

8 f) When a potential leak is identified by a particle count during scanning, the potential leak should be verified by a remeasurement with the probe stationary over the suspect location. While scanning, any abrupt increase in particle counts should be cause for investigation. With the minimum concentrations specified above, a potential leak would be verified with a particle count of over 290 in a 15 second interval. NOTE: The DPC test parameters identified are derived from ISO Test Methods, Section B.6.3 Procedure for installed filter system leakage scan test with a DPC. N pa = C c P L 472 T r N pa = Actual number of particle counts which characterize the designated leak T r = Sustained residence time in seconds. Using the formulas from above and inserting the values specified, we derive our leak verification value of particles cm3 N pa = C c P L 472 T r f) Reported values shall be: cm3 15 seconds sec upstream challenge particle concentration; method used to report concentration (measured or calculated); maximum leak penetration in percent; method used (scanned or probe tested); and name of test (HEPA/ULPA filter leak test). F Filters that cannot be scanned with a discrete particle counter a) When a cabinet is ducted so that the exhaust filter cannot be scanned, it may be leak tested by drilling a hole approximately 0.3

9 inches (1 cm) in diameter in the duct at a downstream location that will produce a well-mixed aerosol and inserting the particle counter sampling probe with rigid extension tubing through the hole. b) With the minimum concentrations specified above, a potential leak of 0.005% would be verified with a particle count of over 145 in a 15 second interval. NOTE: The DPC test parameters identified are derived from ISO Test Methods, Section B.6.3 Procedure for installed filter system leakage scan test with a DPC. N pa = Actual number of particle counts which characterize the designated leak T r = Sustained residence time in seconds. Using the formulas from above and inserting the values specified, we derive our leak verification value of particles cm3 N pa = C c P L 472 T r c) Reported values shall be: cm3 15 seconds sec upstream challenge particle concentration; method used to report concentration (measured or calculated); maximum leak penetration in percent; method used (scanned or probe tested); and name of test (HEPA/ULPA filter leak test). F.5.4 Acceptance F Filters that can be scanned Sustained aerosol or particle penetration shall not exceed 0.01% of the upstream concentration at any point. F Filters that cannot be scanned

10 Sustained aerosol or particle penetration shall not exceed 0.005% of the upstream concentration. Supplementary Materials (photographs, diagrams, reports, etc.): If not provided electronically, the submitter will be responsible to have sufficient copies to distribute to committee members. I hereby grant NSF International the non-exclusive, royalty free rights, including non-exclusive, royalty free rights in copyright; in this item and I understand that I acquire no rights in any publication of NSF International in which this item in this or another similar or analogous form is used. Signature*: David S. Phillips Company: Thermo Fisher Scientific Telephone Number: david.phillips@thermofisher.com Submission Date: 5/5/2016 Please submit to: Al Rose, arose@nsf.org *Type written name will suffice as signature

AUTOMATED HEPA/ULPA FILTER SCANNING SYSTEM FOR LEAK DETECTION AND FILTER PERFORMANCE TESTING

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