HEPA Filters

HEPA filters are high density mats composed of randomly arranged fibers. They are used as air filters to remove particles such as dust, pollen, mold, and bacteria. Although they were originally developed for the Atomic Energy Commission, HEPA filters are also used in operating rooms and are becoming increasingly popular as the household air cleaners.

What Do the Initials HEPA Stand For?

HEPA is an acronym standing for High Efficiency Particulate Air. HEPA filters are able to trap sub micron particles and have an efficiency rate of 99.97%. This makes them ideal for cleaning household air which is typically contaminated with pollutants such as cooking fumes, tobacco smoke, dust and dust mites, as well as spores and pollen.

HEPA filters can be integrated with central heating or air conditioning systems. They are also commonly used on vacuum cleaners to filter the outgoing air. While HEPA vacuum cleaners are an improvement over the standard vacuum cleaner, they do nothing for removing contaminants that are commonly found in modern housing.

Houses today are usually built to prevent the escape of cooled or heated air. While this cuts down on utility bills, it makes the indoor environment highly toxic. Gases and solvents from building materials are released into the home atmosphere where they remain airborne. Without an air filter system, anyone living in this environment can become sick from excessive exposure to these chemicals.

Most household pollutants are invisible. The heavier ones are pulled to the ground by the force of gravity, but lighter gases and particles remain airborne. Most of these airborne particles are smaller than 40 microns which means that conventional filters installed on air conditioners or furnaces are useless in trapping them.

HEPA filters are the only way to trap air particles down to the sub micron size. Tobacco smoke, for example, is made up of particles averaging 0.25 microns and viruses can be as small as 0.1 microns. HEPA filters are the only way to remove these types of contaminants.

What Are HEPA Filters Made Of?

HEPA filters are made of densely compacted fiberglass fibers which are randomly arranged. HEPA filters are different from other filters because they do not function primarily as a sieve, but rather depend on three mechanisms for trapping pollutants and particles.

How Does a HEPA Filter Work?

Of course, large particles will not be able to pass through the openings between the fibers of a HEPA filter, but smaller particles stick to the fibers of the HEPA filter because of one of the following mechanisms:

• Interception, when particles come within one radius of a fiber and stick to it.
• Impaction, when larger particles collide with fibers and embed in them.
• Diffusion, when the smallest particles collide with gas molecules. This slows down their velocity and makes them more are likely to be stopped by the other two mechanisms.

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