The True HEPA Filter Revealed
If you worked in a military or government procurement office the term True HEPA filter would have no meaning. Nor would it mean anything if you were contracting a HEPA filter supplier for industry.Only
in air purifier marketing will you see the term hyped as if it were the
all-important gold standard. This is not necessarily a bad thing. Air
purifier companies have one very good reason for it – Shady competitors
with inferior products dishonestly associate themselves with the HEPA
efficiency standard. The term true HEPA is entirely a marketing
term. In industry, government and military applications a filter is
either HEPA or it isn’t. However, there are different specifications
for defining HEPA.
Defining The True HEPA Filter StandardThe
usual standard for measuring air cleaner efficiency health or cleanroom
purposes is the MIL-STD-282 Method 102.9.1 Dioctylphthalate test (D.O.P
test) which requires the filter to capture 99.97% of 0.3 micron
particles. So a True HEPA filter has the proven efficiency of 99.97% at
0.3 microns by this test. The
European Standard EN1822-1 defines a HEPA filter as ranging from 85% to
99.995% efficient against a 0.3-micron challenge. However, there are
specific filtration grades given to each filter spanning that range.
This allows an end user to know exactly what they are purchasing. In
many respects, it is a better way of expressing air filter
efficiencies.
How Other Filters Compare To True HEPA
A True HEPA filter's D.O.P.-rated efficiency is it’s minimum
starting efficiency. The actual operating efficiency is higher than
that, for all particle sizes from 0.001 micron upwards. The
starting efficiency of any non-HEPA air cleaner is very much lower –
anywhere from 5% to 60% by the D.O.P. test. True HEPA filters are far
more efficient for air cleaning than other types of filtration systems.
Filter systems like electronic air cleaners' aluminum plates or
3M Filtrete media depend on electrostatic charges to attract dust to
its plates or fibers. As the plates or fibers load up with dust, their
ability to attract more dust drops dramatically. An electronic
air cleaner or 3M Filtrete-based air cleaner's starting efficiency is
usually the maximum efficiency. 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. That, plus the fact that most electronic filters
are not very efficient at .3 microns and even worse for particles less
than .3 microns, makes a strong case against electronic filter types.
A Few Facts About True HEPATrue
HEPA filtration is used for nuclear contamination, lead and asbestos
abatement, surgical facilities, tuberculosis wards (the CDC guidelines
for tuberculosis transmission recommend only HEPA filters be used),
clean rooms, computer rooms and other areas where clean and particle
free air is essential.True
HEPA filtration is currently the only type of air purification
recommended by the U.S. Government’s Department of Homeland Security
and FEMA. Contrary to the claims of misleading air cleaner ads,
bacteria and viruses do not breed in true HEPA filters. HEPA filters
provide a dry environment and without moisture there is nothing to keep
bacteria alive, much less breed. These trapped contaminants eventually
die from lack of moisture. This is why only true HEPA filters are used
where health is critical as in hospital operating rooms and ICU wards.
Bacteria can breed within the filter only if the air coming into the
filter is moist. If such is the case, methods for killing bacteria
within a HEPA filter include antimicrobial treatment of the media or a
germicidal ultraviolet light. Though it may only be a marketing
term, it is born of the necessity to counteract the efforts of many
impersonators. There are many air cleaners claiming to have HEPA type
filters. These air cleaners have no specified performance rating, so
you have no way of knowing how good it is. In many cases a high
efficiency furnace filter with a MERV 13 rating would be as good as
these much more expensive air cleaners. My own personal conviction is that buying a HEPA filter air purifier is the best choice I can make. Return to Home Air Purifier Guide homepage from True HEPA Filter article.
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