High efficiency filter specifications and parameters of various international standards
Dispersed oil particulate (schedule) scan testing, also known as filter integrity testing, or leak testing, is one of the most cited industry standard methods.
The test is recommended to be repeated at fixed intervals to verify the efficiency of continuous filtration. During the test, the particulate filter is introduced and the output is measured.
HEPA filter leak testing is required in various international standards, including FDA Guidance for Industry: Aseptic Processing for the Manufacture of Sterile Pharmaceuticals, cGMP and WHO Technical Report Series, No. 961. The Clean Room, ISO 14644-3 standard provides further guidance.
Traditional aerosol photometric testing methods, used since the 1950's, are suitable for measuring 0.003% plan scan tests. To perform an accurate filter leak test, it is necessary to ensure that the aerosol concentration challenge is uniform across the upstream face of the filter(s) being tested; this is known as spatial uniformity. Otherwise, localized high or low concentrations may cause the filter to fail or pass the test in error. ISO 14644-3 indicates that the test aerosol concentration should not vary by more than ±15% over time. The consistency of the challenge upstream of the filter should be verified.
If a cleanroom suite is the target of a test, challenge the aerosol injection after the air handling unit (abstract). When the air enters the filter, the test particles within the duct are well mixed resulting in a greater concentration at each end of the filter.
It is important that the proper flow rate through the test is established prior to the filter. When inspecting the filter leak site, the system should check the following tests described in ISO 14644-3 to verify that the airflow volume, balance and velocity tests, where appropriate, are consistent with these parameters within the specified range. These tests should precede the challenges of conformance testing and leakage testing.
The standard ISO 14664-3 indicates that permeation testing challenges concentration but allows for substitution of 0.01% agreement between the customer and supplier of the standard. FDA guidance, however, indicates 0.01% permeation leakage.
It is best to start scanning the area at the gasket, not the face of the filter, so that any problems with the gasket leak test particle area and to the face of the filter do not cause false reports of leaking media.
After checking the gasket, it is best to continue filtering the media and seal between the casing and then the face of the filter.
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