5.1 Since all sterilizing filtration processes are performed under positive pressure, this test method is designed to assess the retentivity of a sterilizing filter under process conditions.

5.1.1 A challenge of 10⁷ bacteria per cm² of effective filtration area is orders of magnitude higher than one would expect to encounter in a sterilizing filtration process. This level was selected in order to provide a high degree of assurance that the filter would quantitatively retain large numbers of organisms. This concept is important, in view of the requirement to provide a quantitative assessment in validating a sterilization process.

5.1.2 The analytical procedure utilized in this test method provides a method to assign a numerical value to the filtration efficiency of the filter being evaluated. This value, coupled with a knowledge of the number and types of organisms (bioburden) indigenous to the process, may then be utilized to determine the probability of obtaining a sterile filtrate. Conversely, the numerical value of the filtration efficiency may be used when one must meet a specified probability of sterility assurance to calculate the volume of fluid that may be filtered in order to maintain that level of assurance.

1.1 This test method determines the bacterial retention characteristics of membrane filters for liquid filtration using Pseudomonas diminuta as the challenge organism. This test method may be employed to evaluate any membrane filter system used for liquid sterilization.

1.2 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.