Attachment 3 - TE-2 Testing Filters Examples.pdf

U.S. Department of Agriculture

National Bio and Agro-Defense Facility

1980 Denison Ave ■ P.O. Box 1807 ■ Manhattan, KS 66505-1807

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TE-2 Tes�ng and Filter Examples

1. How Is Filter Integrity Testing Conducted?

There are three procedures available to carry out filter integrity testing and these are primarily chosen based on the filter membrane material. Commonly used test procedures for filters with hydrophilic membranes are the bubble point test (BP) and the Forward Flow test (FF), also known as the diffusive flow test or, when gas flow is measured indirectly by pressure changes, the pressure hold test or pressure decay test.

The basic condition for the tests is complete wetting of the filter membrane pores utilizing a wetting fluid such as water, buffer, or the product for filtration. For hydrophobic membranes that will not wet with water, a low surface tension liquid such as a mixture of alcohol and water, is required. An alternative test method, that can be used for filters with hydrophobic membranes, avoiding use of organic solvent in the process, is the Water Intrusion test (WIT), also known as the water flow test.

A bubble point test is traditionally used to test small filter assemblies such as filters installed in a disc holder, cartridge filter housing or capsule. When air or nitrogen pressure is applied to the wetted membrane incrementally, the gas flow across the membrane at each pressure stage is measured. As the pressure increases it will reach a point at which it exceeds the capillary forces of the largest pores in the filter membrane. The automated test equipment will measure the increase in air flow as the wetting liquid is expelled and bulk gas flow occurs. This value is the bubble point and will define a pass or fail when compared to literature values for the filter/membrane. The strength of the bubble point test is its ability to identify pore sized related defects on membranes with a small surface area.

In comparison, the Forward Flow test is a measure of diffusive gas flow across a wetted filter membrane at constant air or nitrogen pressure. The gas flows across the wetted filter membrane by diffusion due to the difference in pressure across the membrane. A pass or fail is easily measured with automated test equipment, with defects being recognized by an increase in flow values beyond a validated maximum.

The Water Intrusion test is used for filters with hydrophobic membranes that cannot be wetted by water but are instead completely covered with water. When placed under pressure using air or nitrogen the penetration and passage of water is repelled by the membrane. However, a very small quantity of water will evaporate and pass through the

National Bio and Agro-Defense Facility membrane as water vapor. This low flow is measured by the automated test equipment with increased water flow beyond a validated maximum being an indicator of a non-integral filter.

These three simple, non-destructive tests can be effectively determined with the same automated test equipment, giving opportunity to ascertain filter integrity for a wide scope that can encompass not only a specific manufacturing process, but provide value within a whole manufacturing facility.

Primary filters to be tested.

ABxPFR7PVH4 Type Filters

Pall Corpora�on, KA02PFRP8 mini Kleenpak filter.

National Bio and Agro-Defense Facility

Secondary filters to be tested.

Cy�va Whatman, 67235000 HEPA inline vent filter.

Camfil Gage Guardian, B-0011809 HEPA inline vent filter.

National Bio and Agro-Defense Facility

MC Air Filtra�on, 355026WP HEPA inline vent filter.