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Inside HEPA Technology and How HEPA Filters Work

HEPA Filters

 When it comes to air quality, and air pollution there are so many things we need to look out for. Particulate matter from factory and car exhaust fumes, volatile organic compounds (VOCs) toxic chemicals, bacteria and viruses, and even airborne particles such as dust mites, mold spores, pollen and pet pet dander. 

If you work in the healthcare sector, a laboratory or research facility, you already know what HEPA stands for and why HEPA Filters are important. But with the emergence of the pandemic and COVID19, the need for HEPA filters has expanded to all indoor settings.

What is HEPA ?

As officially defined by the US Department of Energy, HEPA stands for “High Efficiency Particulate Air”. It is an efficiency standard for measuring the quality of Air Filters, and is also known as “High Efficiency Particulate Absorbing/ Arrestance” filter. 

The roots of the HEPA technology go back to WWII, when a group of American scientists created the first filter that was able to capture radioactive particles released during the creation of the atomic bomb. Since then, the product has been improved and tailored for specific uses, until 1987 when the certification and standard of HEPA was adopted.

Today the HEPA represents a revolution in air quality. If a certain filter or an air cleaner is labeled as HEPA,  it means that it traps 99.5 to 99.7 percent of airborne particles that are 0.3 microns.

What is a Micron and why is HEPA set for 0.3 microns?
Particles can range from ultra-microscopic to entirely detectable to the human eye. 

A micron is a measure unit for particles, one micron is one millionth of a meter.

To make it easier to understand, check this comparison chart:

HEPA Filters

Scientists refer to the micron size (0.3) as the MPPS meaning “Most Penetrating Particle Size”. Research shows that particles of that specific size can bypass air filters more easily than larger or smaller micron particles.

How HEPA Filters Work ?

The modern HEPA filters are made up of twisted interlaced glass fibers that form a fibrous maze. There are 4 different methods in which particles are filtered out from the air.

  1. First Method- Direct Impaction 

 When larger contaminants, like dust or pollen, travel in a straight path into the air filter, they collide with a fiber, and stick to it. This type of filtration is called direct impaction.

  1. Second Method – Sieving Filtration

Filtration where particles become stuck because they are larger than the gap of the two fibers.

  1. Third Method – Interception Filtering

When the airflow is quick and the particles are light enough to reroute around fibers,  they stick to the sides of the fibers.

  1. Fourth Method – Diffusion Filtering 

The small, ultramicroscopic particles move more erratically than larger ones, so they are more likely to hit and stick to fibers.

What Happens When Particles Penetrate HEPA?

There are other technologies that work in concert with HEPA filters to ward off  super-small pollutants, such as smoke, fumes, and other chemicals. Activated carbon filters are often combined with the HEPA filter, like Austin Air HealthMate Plus® HM450. They use small pores in the carbon  to capture some chemicals, odors, and smoke that a HEPA filter might not catch.

Are there Different Forms of HEPA technology standard?

As mentioned above for an air cleaner or filter to be labeled as HEPA, it needs to remove at least 99.5 particles in 0.3 microns. 

For European Standards, HEPA can qualify filtration of 99.5%,while for the US it’s slightly higher and needs to meet 99.7%.

If you have come across the term “True HEPA” or “Ultra HEPA”, it usually refers to the US standard that requires filtration of up to 99.7% of particles smaller than 0.3 microns