Filtration of airborne particulate is most often done with a media filter; like the one you use in your HVAC system. Media filters are referred to as mechanical filters since they use the process of interception to capture the airborne particulate both in and on the media surface.

The interior surface area of most man-made fiber filters contains a very tortuous path for the smaller particle to work its way through. The particle will take the path of least resistance but at some point it will eventually be trapped in the filter media itself. For general duty filters like the ones used as furnace filters, tiny, less than 10 micron particles will pass through the entire depth of the filter until some more dust, or dust cake as it is called, is deposited on the outside of the filter.

From a visual point of view, one can see the variations in filter interior density by simply holding the filter up to the light. The old style fiberglass filters, which are still available, will allow you to see objects through the media as this type of filter is designed to capture very large particles and small leaves without adding to much additional resistance to the air filter. As you go up the ladder in filter efficiency you will find the amount of light penetrating the media to become lower until you see very little light penetration. These denser media filters are much better at trapping the smaller, more harmful airborne particles but also have a much higher air flow resistance as the filter loads up.

Two basic physics theories apply to this mechanical function. Lanmuir’s equation and Brownian motion. Both discuss the random action of any particle in space. Since the movement of the particle is random, having a filter media that is constructed of a dense mesh-like construction, such as cotton or polyester medias, provides a better “interception” platform for which to capture or catch the random particle.  Obviously, the denser the interior structure of the filter media the greater the chance for interception of the particle by the fibers in the media.

This physical process of interception carries through into the HEPA class of filters These filters use a special media that is wet made, like newspaper, and contains thousands of pieces of glass per square inch. The HEPA paper is very fragile so it has to be pleated with inserts and then encased in a metal frame. This media, however, has an extremely dense interior and is designed to intercept, on initial use, 99.99% of all particles 0.3 microns or larger. As it loads up the efficiency increases by a factor of 10.

Pure Air Systems is one of those companies that uses these high end filters. Since 1985 PAS has been a leader in the use of commercial grade, certified HEPA filters in all of its air filtration devices. To learn more about HEPA filters and the complete line of HEPA based air filtration devices please go to our website at: or follow us on Twitter @pureairsystems. You can also find us on Facebook or call us on our toll-free number at: 800-869-8025.

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About the Author: Don Musilli

My name is Don Musilli. I started Pure Air Systems in 1985 and then sold it in 2006. I continue to consult for PAS and write their blog and control their Twitter account. I also, on occasion, make changes to the website. The company is now almost 26 years old and has been a major player in offering commercial grade, high performance HEPA and Carbon based filtration systems for the commercial, institutional, industrial and residential markets.

I currently reside in Englewood, Florida where I write blogs and do social media marketing for a number of clients.

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