What is HEPA Filtration?
According to NIOSH (National Institute for Occupational Safety and Health), a true HEPA filter is one that can trap 99.97 percent of dust particles that are 0.3 microns in diameter.
To put 0.3 microns in perspective, a typical human hair is roughly 50–150 microns in diameter, so a HEPA filter is trapping particles several hundred times thinner!
This does not mean that HEPA filters cannot trap particles smaller than 0.3 microns, because they do! A HEPA filter is comprised of a mat of interlaced dense fibers arranged in many folds and layers to create a fibrous maze to trap particles. An air flow source, typically a blower fan, pushes the particles through this dense web of filter media and traps particles smaller than 0.3 microns by a combination of three different mechanisms; direct impaction, interception and diffusion.