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Optimizing Filtration Parameters

The wide range in performance of air filters makes it
necessary to use more than one method of efficiency testing.
The industry-accepted methods in the United States are
ASHRAE Arrestance, ASHRAE Efficiency, and DOP. For
ASHRAE Arrestance, a measured quantity of 72% standardized air cleaner test dust, 23% carbon black, and 5% cotton
lint is fed to the filter. The efficiency by weight on this specific
test dust is the ASHRAE Arrestance. ASHRAE Efficiency is
a measure of the ability of a filter to prevent staining or
discoloration. It is determined by light reflectance readings
taken before and after the filter in a specified test apparatus.
Atmospheric dust is used for the test. Both ASHRAE tests are
described in ASHRAE Publication 52-76.(44)
In a OOP Test, 0.3 micron particles of dioctylphthalate
(DOP) are drawn through a HEPA (High Efficiency Particulate Air) filter. Efficiency is determined by comparing the
downstream and upstream particle counts. To be designated
as a HEPA filter, the filter must be at least 99.97% efficient,
i.e., only three particles of 0.3 micron size can pass for every
ten thousand particles fed to the filter. Unlike both ASHRAE
tests, the DOP test is not destructive, so it is possible to repair
leaks and retest a filter that has failed.