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The Inner Workings of HEPA Filters


How A HEPA Filter Works Image-Clean Air PlusHEPA air filters represent the industry standard for effective air filtration. While everyone knows that the HEPA designation means high-quality, many people aren't aware of exactly what such filters do or why they're so effective. With a better understanding of how they work, people will gain even more appreciation for their benefits and can make a more informed choice about their air filtration needs. HEPA definitely works, and is something to look for when buying an air purifier. 


HEPA Filters: A Brief History

High-efficiency particulate air (HEPA) filters have been around since the 1940s. They were originally developed for the Manhattan Project, to protect the scientists from the radioactive particles that could spread through the air. The government knew that exposure to such radiation was lethal and they needed a way to safeguard their scientists. The answer was the HEPA filter; its revolutionary design allowed it to capture the tiny radioactive contaminants that remained such a big threat.

How HEPA Filters Work

HEPA filters are so effective because of their innovative design. The filters are comprised of mats made of many borosilicate fibers. These mats are arranged in folds, similar to an accordion. Because of these folds, the filter is able to have a very large surface area with which to trap contaminants, while still being compact in overall size. Many people believe that the fibrous mats simply strain out the harmful contaminants; this is actually not the case. HEPA filters are guaranteed to trap 99.97% of airborne particles 0.3 microns and above. Yet the space between the fibers is actually much wider than 0.3 microns. It may seem counterintuitive, but it wouldn't be feasible or efficient to trap particles this small with a sieve-like filter.

Methods of Particle Filtration

HEPA filters remove contaminants in three ways.

  1. First there is inertial impaction this traps the largest particles – bigger than 1 micron. During this process, when air flows around the fibers of the filter, the particles in the air are too big to change direction. They keep traveling forward until they essentially run right into a fiber, becoming stuck.

  2. The second method by which particles are removed is interception.This applies to medium particles that can flow around the fibers. However, if they pass within one fiber radius, they get stuck.

  3. The third process, diffusion, applies to particles that are smaller than .1 micron.These particles are so small that they actually bounce off of the molecules that make up the air. Though they're small enough to pass by fibers, because of the way they're buffeted by gas molecules, they often bounce around and run right into the fibers. This removes them from the airflow.

Toward Wider Use

Once the technology became commercially available in the 1950s, HEPA filters began to be used in all sorts of commercial applications. Their multilayered approach to filtering contaminants made them very effective and attractive to people who needed to keep environments clean, especially hospitals and manufacturers making sensitive products like microchips or pharmaceuticals. "HEPA filter," as a term, became recognized as a mark of excellence and many companies marketed it this way. In the modern day, in order for a filter to gain a HEPA rating it must meet standards set by the United States Department of Energy.

Benefits of HEPA Filters

These days, many individuals use HEPA filters. They can help improve indoor air quality, by reducing airborne allergens and potentially easing chronic respiratory conditions like asthma and allergies. Many HEPA air purifiers also include other filters like an activated carbon filter, which removes odors, smoke, smog, and many other chemical vapors. An efficient way to remove airborne particle pollution can be extremely helpful for those with sensitivities. Anyone who wants to breathe healthy, clean air should consider purchasing an individual HEPA air purifier.


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  • Administration Staff