The performance of air filters is usually tested in a test unit that consists of a fan, a test duct, the tested filter, two samplers, a vacuum pump, and other instruments. Three test methods with their own test dusts and procedures are used for the testing of low-, medium-, and high-efficiency air filters.

The weight arrestance test is used for low-efficiency air filters to assess their ability to remove coarse dusts. Standard synthetic dusts that are considerably coarser than atmospheric dust are fed to the test unit.

By measuring the weight of dust fed and the weight gain due to the dust collected on the membrane of the sampler after the tested filter, the arrestance can be calculated. The atmospheric dust spot efficiency test is used for medium-efficiency air filters to assess their ability to remove atmospheric dusts.

Atmospheric dusts are dusts contained in the outdoor air, the outdoor atmosphere. Approximately 99% of atmospheric dusts are dust particles <0.3 mm that make up 10% of the total weight; 0.1% of atmospheric dusts is particles >1 mm that make up 70% of the total weight.

Untreated atmospheric dusts are fed to the test unit. Air samples taken before and after the tested filter are drawn through from identical fiber filter-paper targets.

By measuring the light transmission of these discolored white filter papers, the efficiency of the filter can be calculated. Similar atmospheric dust spot test procedures have been specified by American Filter Institute (AFI), ASHRAE Standard 52.1, and former National Bureau of Standards (NBS).

The DOP penetration and efficiency test or simply DOP test is used to assess high-efficiency filters removing dusts particles of 0.18 mm. According to U.S. Military Standard MIL-STD-282 (1956), a smoke cloud of uniform dioctyl phthalate (DOP) droplets 0.18 mm in diameter, generated from the condensation of the DOP vapor, is fed to the test unit.

By measuring the concentration of these particles in the air stream upstream and downstream of the tested filter using an electronic particle counter or laser spectrometer, the penetration and efficiency of the air filter can be calculated.

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