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What is a HEPA filter and how does it work?

HEPA is the acronym of ‘High-Efficiency Particulate Air’. HEPA filters were developed and initially trademarked in the 1950’s, however, over time the term HEPA has become more of a generic name and has a history of being misused when referring to vacuum cleaner filters, water filters and even residential boiler filters.

The most accepted international standard for the classification of HEPA filters is the European EN1822 procedure. The standard defines 8 different filter classes; the higher is the class, the greater the efficiency. Classes E10 to E12 are Efficient Particulate Air (EPA) filters, H13 and H14 are HEPA filters, and U15 to U17 are Ultra Low Penetration Air (ULPA) filters.

The filtration process is mechanical; it works by forcing air through a fine mesh that traps harmful particles. The maximum number of particles that can pass through H14 filter is 5 from 100,000 particles of size 0.1- 0.2 microns (MPPS). HEPA filters are perfect for critical applications such as pharmaceutical, food or beverage manufacture and especially medical facilities. It can also be recommended in areas with high density of people (medium-risk environments) like airports, schools, and other public places.


As per scientific studies, fine particulate matter (PM) air pollution is a leading global public health risk factor. Particularly those particles below 2.5 microns (μm) represent a hazard, as they can enter our bloodstream. Nanoparticles can be as small as 0.1 right down to 0.001 μm.

Well-known bacteria and viruses sizes are as follows:

Influenza A virus: 0.08 - 0.12 μm

HIV: 0.08 μm

Hepatitis C virus: 0.05 μm

Mycobacterium tuberculosis: 1.0 μm


The size for Coronavirus species like SARS-COV-2 (COVID-19), and MERS-COV are from 0.06 to 0.2 μm.

The Centers for Disease Control and Prevention (CDC) explained that coronavirus spreads from person-to-person contact and through respiratory droplets produced by an infected person when he or she coughs or sneezes. However, experts from the National Academy of Sciences told the White House that results of specific studies showed that coronavirus can be transmitted through the air by just talking and breathing.

It is a misconception that HEPA filters could not capture particles below 0.3 μm like airborne coronaviruses. Particles around 0.3 μm are the hardest to catch that it became the measure of effectiveness of HEPA filters. In a study conducted by NASA, the results showed that HEPA filters are highly effective in removing up to 100% of fine (less than 2.5 μm) and ultrafine (less than 0.01 μm) particulate contaminants.

Therefore, it is right to say that viruses can be filtered, and their harmful effects reduced by using a proper and certified HEPA filter.

The ASHE (American Society for Healthcare Engineering) warns about poorly maintained filters with inadequate seals and breaches in the filter media that will promote the passage of contaminants into rooms.

HEPA H13 filter from Eolis Air Manager

Download the HEPA Filtration Explained PDF file below:

HEPA Filtration Explained
Download PDF • 289KB

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