HEPA Filters: What They Are & How They Work

If you’re shopping for an air purifier, you’ve probably run across the term HEPA used in regard to filtration. You may be wondering what a HEPA filter is, or if you’ve heard of it, you may be wondering how it works. HEPA filtration is an important and popular form of air purification technology that must be understood in order to make an informed air purifier buying decision.

What is a HEPA filter?

IQAir HealthPro Plus Air Purifier

HEPA is an acronym that stands for High Efficiency Particulate Air, so a HEPA filter is a High Efficiency Particulate Air filter. Filters, whether for an air purifier or other implementation, come with many benefits and claims.

What sets HEPA filters apart from the rest is their claims are more than just claims. Because in order to be called a true HEPA filter it has to be first be tested and approved, you know exactly what to expect. The Institute of Environmental Sciences and Technology dictates that a HEPA filter must trap 99.97% of particulates 0.3 microns or larger. This does not mean that the filter cannot trap particles smaller than 0.3 microns, because many HEPA filters can; it is simply the threshold that must be reached in order to carry the HEPA name.

What is a micron?

Particles range from ultra-microscopic to entirely detectable to the human eye. Microns, which are one-millionth of a meter, are how particles are measured. To give you a better idea of the size of a micron, or less than a micron, consider that we cannot visually see anything less than 10 microns. Bacteria can be anywhere from 0.3 to 60 microns, and 1 inch equals 25,400 microns.

Micron Comparison Chart:

  • Spores: 3 – 40 microns
  • Mold: 3 – 12 microns
  • Bacteria: 0.3 – 60 microns
  • Car emissions: 1 – 150 microns
  • Pure oxygen: 0.0005 microns

How do HEPA filters work?

To put it simply, HEPA filters trap air contaminants in a complex web of fibers. Depending on the size of the particle, this can happen in four different ways: Inertial Impaction, Diffusion, Interception, or Sieving.

How HEPA Filters Work

Larger contaminants are trapped via inertial impaction and sieving. The particles either collide with the fibers and become trapped or are trapped while attempting to travel through the fibers. Medium sized particles, as they move through the filter, are grabbed by the fibers via interception. Smaller particles are dissipated as they travel through the filter and eventually collide with a fiber and are trapped.

Are all HEPA filters the same?

Contrary to popular belief, not all HEPA filters are the same. There are significant differences in composition and utilization. For example, Blueair uses what they call HEPASilent™ particle filtration technology. The air first passes through an ionizer, which charges incoming particles with a negative electrostatic charge. The air then reaches the HEPA filter, which uses gradient composition of synthetic fibers to capture the charged particles. RabbitAir uses what they call a BioGS HEPA Filter. Rather than just trapping contaminants and having them build up over time, RabbitAir asserts that their filters also reduce contaminants. This, in turn, works to prevent allergen buildup and the further growth of bacteria and viruses on the filter, improving the overall efficiency. IQAir’s HyperHEPA filtration uses what they call nanofibers to stop particles as small as 0.003 microns.

There are many different air purifier technologies out there – activated carbon, ionizing, ozone, UV technology, and HEPA just to name a few. Some air purifiers use technologies in conjunction with each other while others employ only one technology. Whichever you decide to go with, knowing what to expect is important. With HEPA technology, you know exactly what to expect and there’s no guesswork involved. Whether it’s an enhanced HEPA filter or one without any bells and whistles, you can be sure that contaminants will be removed on a microscopic level, so go ahead, take a deep breath.

Recommended Reading:

RESOURCES:
  1. https://www.donaldson.com/en/aircraft/support/datalibrary/042665.pdf
  2. http://www.engineeringtoolbox.com/particle-sizes-d_934.html
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