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HEPA filters are specially made high
grade filters that are designed to remove 99.97% of all pollutants that are
greater than 0.3 microns in size.
The HEPA ("High Efficiency Particulate Arresting") filter was
originally developed during the World War II by the US Atomic Commission to
protect its researchers.
Today, this technology has been widely adapted by various
air purifier manufacturers to produce highly efficent HEPA filter
air purifiers.
"True" HEPA filters are recognized by OSHA/EPA as a proven method of
cleaning the air. It's often regarded as the best form of air filtration.
"Clean rooms" in hospitals, laboratories and high-tech research rooms often
emply HEPA filters to create a contamination free environments.
HEPA air purifiers are excellent at removing dust, pollen, mold, dust mites,
bacteria and other air-borned particles/pollutants. This is because it traps
all particles greater 0.3 micron.
Here's a short list of common air pollutants:
- Pet Dander ................................. (0.5 - 100 microns)
- Pollen ..................................... (5 - 100 microns)
- Mold........................................ (2 - 20 microns)
- Smoke ...................................... (.01 - 1 micron)
- Dust Mite .................................. (0.5 - 50 microns)
- Household Dust ............................. (.05 - 100 microns)
- (dead) Skin Flakes ......................... (0.4 - 10 microns)
- Human Sneeze ............................... (10 - 100 microns)
- Bacteria.................................... (0.35 - 10 microns)
note: 1 micron is roughly 1/100 the width of your hair!
As you can see from the chart above, HEPA filters can filter out most of
the air pollutants in your home except for extremely small air-borned pollutants
such as smoke.
HEPA filters provide a dry environment. This ensures trapped bacteria will
die. Bacteria can only in a moist environment. Some filters may be chemically
treated to kill bacteria or it may include a germicidal ultra violet (UV) light.
Note that a HEPA filter cannot trap viruses as they're smaller than 0.3
microns, but a hybrid air purifier that combines a HEPA filter and a germicidal
UV light will be able to kill both air-borned bacteria and viruses.
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Nov 2001: Exposure to airborne indoor fungi in residential environments can be reduced through use of portable high efficiency particulate air HEPA filter and regular maintenance of filter material and carpets.
Cedric Cheong of Murdoch University Australia presented this new
research at a IAQ 2001 conference.
"Our study showed a 70 percent reduction in airborne indoor fungal levels
and a 38 percent reduction in particulate matter in homes fitted with
portable HEPA filtration units." In Cheong's paper entitled The Use of
HEPA Filters to Control Airborne Indoor Fungi, Cheong stated: " These results
show that the operation of portable HEPA filtration units achieve effective
outcomes in reducing levels of airborne indoor fungi. Outdoor sources remain
the main contributor to indoor sources of fungi..
The study involved asthmatic children between the ages of 6 and 11. Portable
HEPA air cleaners were placed in the children's bedrooms for 15 weeks. He
added that the ongoing study results are being documented by a physician, not
self-reported. In one of the 15 homes being studied, a HEPA air filter has
decreased asthma symptoms and medication of an asthmatic child.
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HEPA air filters look like most other air filters you've seen, many have a pleated media, separators, wet laid filter medium, edge seal, a sealant and are contained in a rigid frame. By their nature, HEPA air purifiers do not lose their efficiency over time. Although, they do have the potential of becoming clogged and blocking airflow.
Other things to note...
When considering a HEPA based air purifier, you need to check the lables to
make sure that the unit has a "TRUE" HEPA filter and not "HEPA-Type"
filters. There is a big difference. The efficiency of a
'Hepa-type' filters ranges from 25% - 95% whereas a
"True" HEPA filter is certified 99.97 efficient.
Another criteria to check is whether the air purifier unit comes with a
prefilter. A prefilter filters out larger particles (1 micron and larger)
before they reach the HEPA filter.
This will extend the life of the HEPA filter
which is significantly more expensive. Most HEPA filters have a lifespan of
2-5 years.
You must check the performance of the fan motor that draw/circulate
air in a room - measured in CFM (cubic feet per minute) of the air purifier.
A high quality filter is of little use if the fan motor is weak and unable to draw
a significant amount of air in the room through the purifier.
A good rule of thumb when you're looking for a quality
portable HEPA Air purifier
should have the following: Fan motor performance between
350 - 400 CFM and power consumption between 80-150W.
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