"To
qualify as a "true" HEPA, the filter must allow no more than 3 particles out of
10,000 to penetrate the filtration media."
High-Efficiency
Particulate Air HEPA filters, formerly called high-efficiency
particulate arrestors, are another option of extended-surface media filtration to
consider.
This unique design was
originally developed during World War II to prevent discharge of radioactive particles
from nuclear reactor facility exhausts. They have since become a vital technology in
industrial, medical, and military clean rooms and have grown in popularity for use in
portable residential air cleaners.
These devices have been
traditionally defined as an extended-surface dry-type filtration system having a minimum
particle removal efficiency of 99.97% for all particles of 0.3 micron diameter with higher
efficiency for both larger and smaller particles. This rating is determined using a test
challenge smoke that consists of particles of 0.3 micron average diameter.
Overall, the American
Lung Association recommends that proven source control strategies be employed as a primary
means of reducing exposure to pollutants. However, physical studies which do not measure
health effects do show that certain air cleaners and HEPA filters are effective in
removing certain indoor air pollutants. Thus, as an adjunct to effective source control
and adequate ventilation, highly efficient air cleaners can be useful in further reducing
levels of certain indoor air pollutants. More research on the health benefits of air
cleaners is needed to provide complete evidence that would better address the
circumstances of intended use. Manufacturers, clinicians, government agencies, and private
industries can all assist with providing and interpreting this research in order to better
inform the public.
Based on the limited available data, we conclude that if allergen sources are present
in a residence, air cleaning alone has not been proven effective at reducing airborne
allergen-containing particles to levels at which no adverse effects are anticipated. Cats,
for example, generally shed allergen at a much greater rate than air cleaners can effect
removal. Dust mites excrete allergens in fecal particles in sequestered environments
(i.e., within the carpet or the bedding). For individuals sensitive to dust mite allergen,
the use of impermeable mattress coverings appears to be as effective as the use of a
laminar flow air cleaning unit above the bed. Source control should always be the first
choice for allergen control in residences.
The reality in most residences is that total elimination of a pollutant source is not
always possible or practical. Individuals with severe allergy and asthma symptoms, whose
symptoms are not alleviated by other source control and ventilation strategies, may want
to try an effective air cleaner in an attempt to aid in further exposure reduction.
Although there is no proven health benefit from such a measure, some individuals report
that they perceive air cleaners as useful in improving their health status. |
