The nomads of the deserts around the world and the people who live in the Middle East deal with these weather monsters on a regular basis. We even see them in the desert southwest in the U.S. on occasion. Huge quantities of ultra-fine sand lifted off the ground by high winds and forming a dust cloud so dense you can’t see five inches in front of your face. What we commonly refer to as a sand storm is actually called a Haboob.

Sand storms or dust storms have been around since man first walked on this earth. While the term Haboob may indeed be the correct technical term for these storms, using the more generic and logical term of sand storm describes exactly what it is. And, these storms can create a lot of damage and can be very dangerous to your health if you are caught in one. But dust and sand can, in some instances, be your friend.

In order to remove dust and sand from the inside of a home or building media air filters are placed in the HVAC systems to trap and collect these airborne particles. Without the filters the dust would eventually cover everything. And, without the dust build up on the surface of the filters, the ability to remove the finer,  lung damaging particles would be difficult to do.

The majority of the media used in the manufacture of air filters is either polyester, cotton, a blend of the two, synthetic fibers or fiber glass. While some of these medias can better trap and hold dust and dirt while they are clean, the real filtration takes place when all of these filters get dirty.

The dust cake or filter cake, as it is called, is the layer of dust that sits on top of the filter surface and is usually a dirty grey or sometimes blackish in color. You can see this dust layer on the filter after a few weeks  of operation. In a very dirty environment you may see this filter cake forming even earlier. The filter medias are designed to capture as much of the smaller, under 20 microns in size particles as possible, without adding too much air flow resistance to the HVAC blower/motor assembly.

The filter cake actually enhances the overall effectiveness of the filter media by adding this first “dust cake” filtration layer which is more porous but also more dense than the media itself. As a result some of the smaller, sub-micron particles are trapped in the filter cake before they even see the base filter media. The deeper the filter cake the better the overall filtration efficiency. Also the deeper the cake the higher the resistance. For most applications replacing the dirty filter once every 3 months is best.

For more information on air filtration, dust loadings and how to select the best air filter for your application, please go to our website at; or follow us on Twitter @pureairsystems or like us on our Facebook page. Of course you can always 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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