U.S. Department of Homeland Security Recommends HEPA filters.
What happens to germs and other contaminants that get trapped in HEPA filters?True HEPA filters trap germs and other contaminants. These trapped contaminants eventually die because of lack of moisture. This is why only True HEPA filters are used where health or cleanliness is critical – e.g. hospital operating rooms, hospital ICU wards, cleanrooms, electonic laboratories, etc. Doctors and cleanroom engineers continue to prefer True HEPA filters because they are effective at removing germs and other submicron contaminants.
What about dust mites in my filter?
It is unlikely that your air cleaner would trap dust mites. This is because they are too large to go airborne easily. However, when dust is disturbed, dust mite dropping (which is the real allergen causing allergic responses) is small and light enough to go airborne. It is this allergen that is trapped by True HEPA filters. Since few dust mites are captured in the filters themselves, there is little chance of them breeding or even surviving. They would die from lack of moisture.
If it were true that HEPA filters were breeding grounds for dust mites and germs, then they would not be used in hospitals and cleanrooms.
How does HEPA filtration compare to other types of filtration - like those electronic filters?
The usual standard for measuring air cleaner efficiency (and for health or cleanroom purpose) is 0.3 microns, which is the cleanroom-standard D.O.P. test (Mil-Std 282 Dioctylphthalate test, or the Potassium Chloride KCL test). So a True HEPA filter has the highest proven efficiency of 99.97% at 0.3 microns by this cleanroom-test. The efficiency of any non-HEPA air cleaner is very much lower – anywhere from 5% to 60% by the D.O.P. test at 0.3 microns. And because all non-HEPA efficiencies drop with usage, their real operating efficiencies are even lower - probably between 1% to 15% within hours or days for portables. HEPA filters are far more efficient for air cleaning than other types of filtration systems.
Tell me more about electronic filters. I've seen them so much on TV and I'm tempted to buy one.
A True HEPA's D.O.P.-rated efficiency (which is 99.97%) is the MINIMUM STARTING efficiency. The actual operating efficiency is higher than that, for all particle sizes (0.001 micron upwards).
However, other types of filters, like electronic air cleaners' aluminum plates, or 3M Filtrete media, depend on electrostatic charges to attract dust to its plates or fibres. As the plates or fibres load up with dust, their ability to attract more dust drops dramatically. This is akin to a magnet that would find it harder to attract more iron filings if it already has a lot of iron filings on its surface, as the magnetic force is diminished.
Therefore, an electronic air cleaner, or 3M Filtrete-based air cleaner's starting efficiency is the STARTING efficiency, and is usually the MAXIMUM efficiency. That is, with use, the efficiency will drop very fast, and the average operating efficiency is much lower. Some published studies have shown that an electronic air cleaner's efficiency can drop to one-fifth of its starting efficiency within 26 hours of operation. Couple that with the fact that most electronic filters are not very efficient at .3 microns and even worse for particles less than .3 microns, you have a strong case against electronic filter types.
The History of HEPA Filters
The first HEPA filter (high efficiency particulate air) was designed in the 1940's by the research and development firm Arthur D. Little under a classified government contract as part of the Manhattan Project, where the first atomic bomb was developed during World War II. A major advancement in air filtration technology, the filter solved a critical need to control very small particles which had become contaminated by nuclear radioactive sources.
Considering the condensation nuclei of radioactive iodine to be most harmful, researchers focused on the ability to capture solid particles that were created through the condensation of gases and liquid aerosols into solid matter. Having identified 0.3 micron size particles as the most penetrating size particle and representative of the particle of concern, 0.3 microns was established as the particle size fraction at which to determine filter efficiency performance.
Because of its effectiveness, the filter was originally refered to as an "absolute filter." The generic acronym HEPA came into use some time following 1950 when the filter was commercialized and the original term became a registered tradename.
Over the next 50 years, HEPA filtration gradually evolved as technological breakthroughs in aerospace, pharmaceutical processing, photographic film manufacturing, data processing and microcircuitry demanded higher and higher levels of air cleanliness. If not for HEPA filtration, such milestones as the lunar landing and the introduction of the silicon chip might not have been achieved and adequate control of hazardous and toxic particulate would not be possible.
Today, the HEPA filter has been intruduced into common environments like in our homes and places of work for better health and environmental control.