HEPA filters

What are HEPA filters?

HEPA stands for High Efficiency Particulate Air or High Efficiency Particulate Arrestance. A HEPA filter is a highly efficient form of air filter which is designed to remove very small particles from the air. HEPA filters are often used in commercial and residential air purifiers, and in vacuum cleaners - as they excel at removing particles such as pollen, mold and dust from the air. HEPA filters are also often found in medical applications - a good indicator of their quality.

HEPA filters are commonly used in both stand-alone air purifiers and in HVAC (Heating, Ventilation and Air Conditioning) systems. The best HEPA filters are highly efficient at cleaning the air but require fans to draw the air through the filter - which can sometimes be noisy. Many HEPA filter units have specifications for their sound level - measured in decibels (dB). This factor is worth considering if for example you are thinking of putting a standalone HEPA filter unit in your bedroom.

To achieve true HEPA specifications the filter must be able to remove 99.97% of particles .0003 of a millimeter in size. This particle size is considered the hardest to filter from air - both smaller and larger particles are more efficiently removed. HEPA filters cannot remove toxic gases from the air - only solid particles.

HEPA filters are likely, however, be effective against viruses. Studies have shown that HEPA filters are 99.99% efficient against particles in the same size range as most viruses. ( source - http://www.envirco.com/faq.asp )

HEPA filters are also likely to be effective against some radioactive particles. It is interesting to note that HEPA filters were originally developed in the 1940s as a way to filter radioactive particles from the air. Survivalists, take note! Some air-purifier manufacturers such as Aller appear to have designed units with survivalists in mind.

Often, filter systems with HEPA filters have more than one stage. The first filter stage is more of a "general air filter" or "pre-filter" which removes the larger particles and "dust bunnies" and protects the more expensive HEPA filter from early loss of performance. The HEPA filter then removes finer particles. HEPA filters do not typically require maintenance until it's time to replace - and may even increase in efficiency over their lifetime.

What can we learn about HEPA filters from "cleanrooms"?

There are many facilities in the world known as "cleanrooms". A cleanroom is a special industrial facility, usually used for either scientific research or for state-of-the-art manufacturing, that requires a highly controlled environment free from dust or other contaminants. The most famous cleanrooms in the world are ones used by the big scientific establishments - such as the incredible NASA SSDIF (Spacecraft Systems Development and Integration Facility) cleanroom used for work on space hardware projects such as the Hubble Space Telescope. Cleanrooms are graded and given classifications according to the number of particles in the air - and are much, much cleaner than your kitchen even after you have been scrubbing it all morning.... ;)

Now unless like NASA you have megabucks to spend, or are absolutely obsessed with cleanliness, a cleanroom is obviously not a realistic option. However, it might be highly revealing for us to examine cleanrooms - because they really do need dust solutions that are guaranteed to work! So if we can learn what they are using, we have a pretty good idea of what might be effective in our own personal quest for pure air.

And what do we find...? The sparkling, state-of-the-art NASA SSDIF cleanroom, which NASA's official web site nasa.gov claims is "1,000 times cleaner than a hospital operating room", uses HEPA filters continuously to purify the air! Ok, so it's a gigantic, top-grade HEPA filter covering one entire wall - but I think we can safely say that if NASA uses HEPA filters in mission-critical applications... they probably work.

Summary

In summary, HEPA filtration has become the industry standard for particulate filtration in environments where air quality is of critical importance - such as cleanrooms and hospitals.

A sparkle-fresh NASA cleanroom facility, complete with spacecraft under construction. It's so spotlessly clean in there that we imagine you could possibly eat your dinner off almost anything (horizontal) in this room - although it might upset a few people so please don't tell NASA it was our idea. Have you ever tried cleaning tomato ketchup off a solar panel in zero gravity? Didn't think so.