Test standards for media in disposable air filters

Test standards for media in disposable air filters

Filter media in this group include those formed from fibrous materials, including natural or synthetic organic fibres and glass fibres. In their gross structures, these media have the form of nonwoven fabrics, wet-laid papers, or air-laid glass fibre mats spun from continuous fibres or blown from molten glass. Some membranes and open-cell foams also have fibrous structures. The solids content of these media is low, with the fibre volume typically less than 10 % of the volume of the media. These media range in thickness from a fraction of a millimetre to several centimetres.

Creating a test standard to cover such a variety of materials is not easy. Both national and international standards bodies, government agencies, technical societies and individual manufacturers have laboured to produce test standards for different attributes of this category of filters, and the media used in them. We discuss here only one standard, ISO/DIS 29463-3 ‘High efficiency filter and filter media for removing particles in air - Part 3: Testing flat sheet filter media’. This draft of a standard prepared for approval by the ISO (International Standards Organization) Technical Committee 142 (‘Cleaning equipment for air and other gases’) members defines a test method for flat sheet filter media used in the manufacture of high-efficiency filters. ‘High efficiency’ is defined here as 95% to 99.999995% at the Most Penetrating Particle Size (MPPS). The standard builds on earlier standards and method descriptions such as ASTM F778-88, IEST-RP-CC021.3, and EN 1822-3:2009.

petri dish     string wound filters     active carbon filters

Under ISO/DIS 29463-3, the test of particle penetration can be performed in either of two ways: using an aerosol having essentially a single particle diameter (a monodisperse aerosol) and condensation nucleus counters, or, using a polydisperse aerosol and light-scattering particle spectrometer/counters. Separate counters may be used, or a single counter may be switched from downstream to upstream.

The table of contents of this draft standard shows the many details which such a standard must address. Every user will not agree with all the choices made by the standards writing committee. Indeed, we point out some weaknesses in the paragraphs below. Items covered in the draft include: 

SPE Cartridge      Syringe       petri dish     string wound filters     active carbon filters     96 well plates     roller bottle     tissue culture flask