ASTM F1368-92

1.1 This test method covers thin filter media, especially membranes, in an effort to determine the largest particle a medium may let pass.

1.2 Batches of microspheres are used as test particles where, in any one batch, all of the microspheres are the same size, and, from one batch to the next the diameters range from 0.1 to 2 [mu]m. Filtration efficiency is determined by comparing the optical density of the feed stream to that of the filtrate, during separate filtration tests, with separate batches of microspheres.

1.3 By sieving filtration is meant that adsorptive filtration is minimized. That is, even though the length of the average pore (defined by the flow of fluid) may be a thousand times the diameter, the present procedure strives to minimize the capture of particles by the walls of the pores. To this end the procedure employs a surfactant in the suspension, a high velocity of the liquid, and a high concentration of test particles.

1.4 This procedure excludes those filter media with charged surfaces that are meant to enhance adsorptive filtration.

1.5 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to use.

1.6 The values stated in SI units are to be regarded as the standard.