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Explainer: What Is a True HEPA Filter?

In recent years, there has been an increased awareness of the importance of indoor air quality. Studies have shown that indoor air quality can be two to five times worse than outdoor air quality due to the large number of pollutants found in modern homes. Jonathan Levy, an environmental health professor at Boston University’s School of Public Health, went as far as to call indoor air pollution one of the unrecognized environmental justice issues of our time.

To improve indoor air quality, many families have invested in various mechanical purifying systems. The manufacturers of mechanical air purifiers often advertise that their products feature something called a True HEPA filter, but consumers seldom understand what the term “True HEPA” means and how the filters described by it differ from traditional HEPA (High-Efficiency Particulate Air) filters.

The Truth About True HEPA Filters

HEPA filters were developed by the Atomic Energy Commission to protect workers on the Manhattan Project from radioactive contamination. All HEPA filters consist of a finely pleated fabric-paper sheet made of highly compressed fiberglass of a very fine diameter. The fabric-paper sheet is typically housed in a metal or plastic frame with a seal around it to prevent air particles from escaping.

Initially, the manufacturers of HEPA filters followed their own internal standards, but the United States Department of Energy eventually standardized HEPA filters, requiring them to remove at least 99.97 percent of airborne particles that are 0.3 microns in diameter.

The European Union also released its own HEPA specification, the European Norm EN 1822:2009, which defines several classes of HEPA filters based on how many percents of airborne particles that are 0.3 microns in diameter are retained.

The term “True HEPA” wasn’t conceived by the United States Department of Energy nor the European Union, but by marketing professionals who simply wanted to emphasize that the HEPA filters contained in the products they were advertising meet the American standard.

Are 0.3 Microns Enough?

Considering that bacteria are anywhere from 0.3 to 60 microns in size, you might be wondering whether 0.3 microns are enough to protect you against indoor air pollutants. The reason why HEPA specifications are concerned with 0.3 microns and not, for example, with 0.1 microns or 1 micron (one-thousandth of a millimeter) has everything to do with something scientists call MPPS.

MPPS, short for Most Penetrating Particle Size, is the size at which particles evade air filters more than larger or smaller particles. As you might have already guessed, MPPS is exactly 0.3 microns. In other words, a HEPA filter that can capture 99.97 percent of airborne particles that are 0.3 microns in diameter should be able to capture just as many particles that are slightly smaller or larger.

What Kind of Air Pollutants Can True HEPA Filters Trap?

The following micron comparison chart should help you understand what kind of air pollutants can True HEPA filters trap:

  • Pure oxygen: 0.0005 microns
  • Bacteria: 0.3 – 60 microns
  • Car emissions: 1 – 150 microns
  • Spiderweb silk: 3 – 8 microns
  • Mold: 3 – 12 microns
  • Spores: 3 – 40 microns

The ability of True HEPA filters to remove pollen, hair, dust, mold spores, and other air pollutants makes them great for allergy relief, asthma support, and healthier living in general. True HEPA filters have already established their place in hospitals, food manufacturing facilities, or the microelectronics industry, and they can be tremendously useful at home.

That said, even True HEPA filters do not filter out gasses and odor molecules, which is why they are often combined with activated carbon filters to provide filtration of volatile organic compounds (VOCs), chemical vapors, cigarette smoke, and household odors.

Quilo 2.0 with a True HEPA Filter

The good news is, the Quilo 2.0 is equipped with two interchangeable cartridges that instantly transform the fan from a cooler or humidifier into a three-stage, true HEPA air purifier. Airborne allergens are trapped in the ultra fine mesh of the HEPA, while odors are absorbed into the active carbon pre-filter. The Quilo 2.0’s third stage of air purification stage is an ionizer, which negatively charges dust particles away from your living spaces and into the confines of the filter. 

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