Why does HEPA Filters have 0.3 Micron Pore Size?

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●High efficiency particulate air filters
HEPA are used to maintain the area cleanliness in classified area. Pore size of these filters is always 0.3 microns with efficiency rating of 99.97%.
● To give you an idea of the size of a micron, it takes 25,400 microns to equal 1 inch (2.54 cm). Conversely, 4/100,000ths of an inch equals one micron. In metric terms, a single micron is 1 millionth of a meter.
●The rating for a HEPA filter is based on capturing nearly all microns .3 in size, verses .1 or even .001 because .3 microns are the hardest size to trap and the optimal size for passing into the human respiratory system. Therefore the .3 micron efficiency rating sets the highest standard.
●A HEPA filter is so efficient that for every 10,000 particles that enter the filter within its filtering range, only 3 particles will get through. Surprisingly, HEPA filters become even more efficient the longer they are in use.

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