What is a HEPA filter, simply?

A commonly used and often misunderstood acronym in the IAQ / HVAC industry is HEPA. 

A HEPA filter is a High Efficiency Particulate Air [Filter] and is made of a pleated media, completely sealed in a frame, that uses mechanical filtration principles to remove at least 99.97% of any airborne particles with a size of 0.3 microns (µm). 

It is imperative to understand that the design around 0.3 micron is specified because it has been tested and identified as the most difficult to capture. In the filtration industry this “worst case” contaminate size is identified as MPPS (most penetrating particle size) and will have even higher capture efficiency (>99.97%) on any particles larger or smaller than the MPPS. It has been scientifically proven that HEPA filters are more efficient at capturing particles that are larger than 0.3 microns and smaller than 0.3 microns.

The filtration principle relied on to achieve this capture rate of submicron particles is called diffusion. This method can be explained with Brownian motion, which is the random movement of microscopic particles suspended in a medium (liquid or gas) caused by collisions between those particles and the molecules of the medium. 

The important takeaway from this is that the industry using this baseline of the (0.3 micron) most difficult size to capture provides an easily understood design efficiency rating and can be tested and regulated by governing bodies like IEST (Institute of Environmental Sciences and Technology)

Claims of HEPA filters not being able to, or needing additional technologies to capture anything below 0.3 is an indicator of a fundamental misunderstanding of filtration basics and a common trend in today's world of suppliers trying to react to the increased awareness of filtration. The true experts are the ones that have been focused before and will be focused long after the spotlight moves on. 

For more information please contact Bairco!