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FAQs About Killing Microorganisms on a HEPA Filter with UV-C Lamps
(Questions with links to answers below)
Healthcare personnel often ask the product design staff at Abatement Technologies
why we developed separate, external UV-C modules for our HEPA-CARE HEPA filtration
systems instead of incorporating UV-C lamps directly into the unit. Here are
some of the most common questions and issues that healthcare professionals
should consider:
- How is UV-C exposure quantified?
- UV dosage, which is typically expressed in microwatts
per square centimeter, is based on four factors:
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- Direct exposure to the UV-C irradiation source
- The intensity of the UV-C source
- The distance away from that source
- The duration of exposure
Because organisms in rapidly moving airstreams are exposed to the UV-C
source for only fractions of a second, effective disinfection requires
very high intensity UV-C output, and very close proximity to the lamps.
This is especially true for more complex organisms such as fungi, which
typically require five to 20 times more UV-C energy to destroy than
bacteria. |
- Why is proximity
to the lamp so important?
- Studies have shown that UV-C dosage decreases by approximately
the square of the distance from the lamp. In other words, compared to dosage
one inch away from the lamp, dosage is four times lower at 2 inches away,
sixty-four times lower at 8 inches away and 144 times lower at 12 inches
away. In some air filtration systems, organisms that pass the lamps or are
trapped on the media can be as far as 12 to 48 inches away from the lamp.
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- Can UV lamps
shining on the inlet face of a HEPA filter kill all of the organisms trapped
on the media?
- This would be highly doubtful because the lamp can't kill
what it can't "see". HEPA filters are designed with very closely spaced
pleats, with typical pack depths of anywhere from three to four inches up
to 12 inches. It's highly unlikely that a lamp or lamps shining on the inlet
face of a HEPA filter would expose microorganisms trapped on the inlet surfaces
of the pleated media pack much beyond the first half-inch to one inch of
depth, especially for pleats that are farthest away from the lamp(s). As
a result, effectiveness would likely be limited to only a small percentage
of the media area.
- Why should contaminated air be
filtered before it reaches the lamp(s)?
- Filtration systems that do not prefilter air before it
gets to the lamp(s) and the HEPA filter can expose the lamp(s) to larger
dust and dirt particles. This can result in formation of a dirt film deposit
on the quartz glass and significantly reduced UV-C intensity. In addition,
agglomerated dirt particles that form on the HEPA filter media can reduce
airflow and filter capacity, shorten filter life and further block UV-C
exposure to organisms that may be trapped beneath them. With the design
of an Abatement HEPA-CARE Air Purification System, air is prefiltered and
HEPA filtered before it is exhausted into the UV-C module, thus maximizing
UV intensity to kill microorganisms.
- Couldn’t a prefilter be
used to reduce lamp-contamination problems for the internal lamp systems?
- Yes, but then the prefilter media must be protected from
exposure to the lamp(s). High-intensity UV-C radiation can rapidly break
down and pulverize most prefilter media, especially synthetics, cotton and
blends. Exposed components such as electrical wiring and rubber gaskets
can also be degraded if not protected properly. HEPA media is much more
UV-resistant, but lamps must be still kept far enough away from the media
to ensure that the UV-C energy won’t destroy filter integrity by breaking
down filter binders and adhesives, and won’t cause VOC off-gassing.
- How are patients and workers
properly protected from accidental UV exposure?
- Because direct UV-C lamp exposure can seriously damage
the eyes or the skin, extra precautions are needed to ensure that patients,
healthcare workers or maintenance personnel are not exposed to the UV-C
lamps during normal use or when replacing filters. This is a much more difficult
task when the lamps are located on the inlet side of the HEPA filter.
With our design, the separate UV-C modules keep the lamps isolated from
the filter compartment, and are accessed only about once a year for lamp
replacement. Built-in safeguards, such as electrical interlock switches,
instantly deactivate the lamps when the access door is opened. It is also
very important to ensure that the overall unit has been safety tested and
certified by a Nationally Recognized Testing Laboratory (NRTL) such as UL,
ETL or CSA. Abatement's germicidal UV-C modules meet this requirement.
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