What is an HEPA Filter? What They Are & How They Work
Indoor air pollution is among the top five environmental health risks. Usually the best way to address this risk is to control or eliminate the sources of pollutants, and to ventilate a home with clean outdoor air.
HEPA is an acronym that stands for High Efficiency Particulate Air, so a HEPA filter is a High Efficiency Particulate Air filter. Filters, whether for an air purifier or other implementation, come with many benefits and claims.
What sets HEPA filters apart from the rest is their claims are more than just claims. Because in order to be called a true HEPA filter it has to be first be tested and approved, you know exactly what to expect. The Institute of Environmental Sciences and Technology dictates that a HEPA filter must trap 99.97% of particulates 0.3 microns or larger. This does not mean that the filter cannot trap particles smaller than 0.3 microns, because many HEPA filters can; it is simply the threshold that must be reached in order to carry the HEPA name.
Pollutants that can affect air quality in a home fall into the following categories:
- Particulate matter includes dust, smoke, pollen, animal dander, tobacco smoke, particles generated from combustion appliances such as cooking stoves, and particles associated with tiny organisms such as:
- dust mites
- molds
- bacteria
- viruses
- Gaseous pollutants come from combustion processes. Sources include gas cooking stoves, vehicle exhaust and tobacco smoke. They also come from:
- building materials
- furnishings
- the use of products such as
- adhesives
- paints
- varnishes
- cleaning products
- pesticides
HEPA filter effectiveness significantly diminishes as the particles become smaller. As particles become very small, they cease to behave so much like particles as they do gas phase molecules. It is difficult to tell whether such small particles are actually suspended in air (particles) or diffused throughout it (gas or vapor). The bottom boundary where particles act as true particles is about 0.01 micron. The normal theory of separation does not apply to particles below this size and removing them from air requires techniques reserved for gaseous materials, like the Air Oasis technology. Particles above 0.01 micron are usually considered to be filterable. Particulates smaller than 0.01 include pesticides, herbicides, some atmospheric dust and nearly all viruses. Plus HEPA filters do not remove gases or VOCs (volatile organic chemical) off gassed from most new carpeting, building materials, furniture, etc.
How do HEPA filters work?
To put it simply, HEPA filters trap air contaminants in a complex web of fibers. Depending on the size of the particle, this can happen in four different ways: Inertial Impaction, Diffusion, Interception, or Sieving.
Larger contaminants are trapped via inertial impaction and sieving. The particles either collide with the fibers and become trapped or are trapped while attempting to travel through the fibers. Medium sized particles, as they move through the filter, are grabbed by the fibers via interception. Smaller particles are dissipated as they travel through the filter and eventually collide with a fiber and are trapped.
And here is my choice for home :
https://www.dyson.com.tr/fanlar-ve-fanl%C4%B1-%C4%B1s%C4%B1t%C4%B1c%C4%B1lar/purifier/pure-cool/pure-cool-white-silver.aspx
Sources :
https://www.epa.gov/indoor-air-quality-iaq/guide-air-cleaners-home#Introduction
https://inspiredliving.com/airpurifiers/hepa-filters.htm
http://www.businessinsider.com/best-air-purifiers-buying-guide-2016-6
Further reading if you would like to buy ;
https://www.rodalesorganiclife.com/home/best-air-purifier-reviews