HEPA filter

The HEPA technology (high-efficiency particulate air/high-energy particulate arresting) was initially developed in the nuclear industry. It was needed in order to catch and clean up dangerous, radioactive particles. Fortunately, most of us don’t have to deal with such things but the HEPA filter is now mostly known for being used in vacuum cleaners. Even inside your home, there are things like dust mites and dirt from outdoors that the HEPA filter can take care of.

Indoor air pollution can contribute to allergies and asthma. If you use an ordinary vacuum cleaner, you might simply be rearranging the dust. Naturally, your vacuum will trap some of the dust inside the bag or filter but let the rest pass back into the room. If you suffer from asthma or allergies, you may find a HEPA filter well worth the investment.

 

How does a HEPA filter work

The most basic filter is a sieve. It has holes that are small enough to trap some particles and big enough to let others pass through. This is how all vacuum cleaner filters work, but here comes the real question. How do you catch smaller dirt particles as well? One option would be to install a very fine filter. Another is that you could put several filters on top of one another, but they would clog up quickly. Also, you’d need a more powerful motor that would use more energy to run.

HEPA filters use different methods to clean the air. There are one or more outer filters that stop the larger particles such as dirt, dust and hair. Inside them, there is the HEPA filter that looks like folded paper designed to trap the smaller particles. It is actually made out of very dense glass fibers and it doesn’t simply work like a sieve.

At high air speeds, some particles are caught by the impact as they smash directly into the fibers. Others get caught by interception as they flow along in the moving air stream. At lower air speeds, dust particles tend to wander about more randomly through the filter (known as Brownian motion) and stick to its fibers by diffusion.

 

HEPA filter

 

What can a HEPA filter remove

It is important to remember that a true HEPA filter can trap 99.97 percent of dust particles that are 0.3 microns in diameter. A typical human hair is approximately 50–150 microns in diameter so a HEPA filter can trap particles that are hundreds of times smaller than a strand of hair. Some examples of such particles are:

  • bacteria (0.35-10 microns)
  • mold spores (2-20 microns)
  • pollen (5-100 microns)
  • pet dander (0.5-100 microns)

On the other hand, HEPA filters alone do not capture odors, germs, cigarette smoke or chemical fumes because their particles are smaller than 0.3 microns.

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