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Q: Effect of ultraviolet light on pathogens and human health consequences ( Answered 4 out of 5 stars,   5 Comments )
Subject: Effect of ultraviolet light on pathogens and human health consequences
Category: Science > Biology
Asked by: seekeroftruth2-ga
List Price: $27.00
Posted: 29 Jan 2006 11:15 PST
Expires: 28 Feb 2006 11:15 PST
Question ID: 438958
I have asthma.  My husband wants to install an ultraviolet light in
our home furnace to clean our air.  It is my understanding that the
ultraviolet light will cause damage to the DNA of the bacteria and other
pathogens that pass through the furnace, and some will be killed. 
Since only a small percentage of home air passes through the furnace,
and since the pathogens that do pass through will mostly be subject to
a brief period of ultraviolet radiation, I think we will end up with
mutated pathogens in our air.  That seems dangerous to me.  Will a UV
light in our furnace pose a health benefit or a health risk?
Subject: Re: Effect of ultraviolet light on pathogens and human health consequences
Answered By: crabcakes-ga on 30 Jan 2006 12:23 PST
Rated:4 out of 5 stars
Hello Seekroftruth,

   When evaluating the actual efficacy of devices such as an air
purifier, it?s important to review studies from an impartial source.
Claims from manufacturers can be biased and present data in a skewed
manner. Since asthmatics (which I am) are affected by a  number of
things, such as dust, animal dander, pollen, smoke, fumes, and surface
mildew, I have always questioned UV light cleaners for a heating
system. My research leaves me with a neutral feeling on these
cleaners, as I a not impressed. It seems these devices won?t hurt you,
and can indeed destroy some organisms like some species of bacteria
and molds ? but are ineffective on gases (Foraldehyde, chlorine,
household cleaners, paint,etc.) smoke, fumes, dust, etc.  Does your
air conditioning share the same ductwork? If not, what about warm
weather? Speaking of duct work, having your ducts cleaned would be a
good thing to do regardless of the UV light. You can also purchase
special allergy filters for your air intake to your furnace/HVAC
system. Consider a good HEPA room filter or two. I have posted reviews
of many brands below. Most filter all lung irritants.

  A disclaimer from one of the air filter review sites says it best:
?The actual effectiveness of an air purifier depends on a variety of
factors including, the amount of air that the air purifier processes,
the nature of the pollutant, and the rate at which the pollutant is
being introduced into the environment.
Additionally, there is no guarantee that an individual who suffers
from allergies or other respiratory problems will derive a discernible
reduction in symptoms through the use of these or other air purifiers.
Whether individuals will derive such relief depends on many variables,
including the source and severity of their allergies, whether the
allergens at issue tend to remain airborne, the rate at which the
allergens are emitted into their homes or offices, and other
environmental factors.?

  ?This is UV of a specific type (253.7 nm wavelength) known to kill
germs contained in the tiny airborne droplets (droplet nuclei) that
transmit some infections (measles, tuberculosis, influenza) from
person to person within buildings. Germicidal UV is aimed at the upper
room air so that only airborne droplet nuclei are directly exposed.
Room occupants are exposed only to low levels of UV reflected from
ceilings and walls - levels below that are known to cause eye
irritation. Germicidal UV has been used safely and effectively in
hospitals, clinics and laboratories for more than 50 years. UV is not
useful for disinfecting the surfaces of objects, or large respiratory
droplets, and does not prevent transmission of infections (e.g.,
colds) spread by large droplets or by direct person to person

?The percentage of airborne organisms rendered on-viable depends among
other factors:a. The intensity of UV radiation.
1.	The intensity of UV radiation.
2.	The length of time of exposure to the UV radiation.
3.	The relative humidity.
4.	The air temperature.
5.	The microbial species.
UV-C is most effective against the very tiniest of airborne
contaminants sizes most difficult to control with standard methods.
?	UV-C does not depend on a perfect air seal to be effective.
?	UV-C destroys rather than trapping airborne pathogens so there is no
risk shaking loose contaminants during service.
?	UV-C does not degrade in the damp environments, that are so often
home to ductwork contaminants, as do media type filters.
?	UV-C leaves no residual chemicals which could cause the "cure to be
worse than the disease" in indoor environments.
?	Inexpensive to install, operate and maintain.
?	Easily tailored to the level of risk involved without sacrificing
control of smaller micro-organisms such as viruses.
?	UV-C can be used in conjunction with other types of air cleaning
systems to tailor the level of protection to the risks involved.
Please see this page for complete information.

  ?UV air purifiers bombard air with ultraviolet light, theoretically
purifying the air of bacteria, pollen, mold spores and such. UV air
purifiers range in size from small portable units, designed to clean
the air in one room, to larger furnace duct-mounted models, like the
one you saw advertised, for sterilizing all the air in the building.

UV air purifiers commonly use two kinds of UV light. UV-C destroys the
cell's DNA while UV-V oxidizes gases, destroying odors and breaking
apart some particles. Not all UV air purifiers use both forms of UV
Their effectiveness depends on a number of factors, including: 
?	Exposure time: UV light effectiveness depends heavily upon the
length of time that cells are exposed to it. Many UV air purifiers are
not effective because the air moves through the filter too fast.
?	Light intensity: UV light intensity drops off sharply with distance.
A common misconception about heating system UV light sources is that
the light will treat ALL the air passing by it. Not true. Air on the
opposite side of the duct does not receive enough light intensity to
be effective.
?	Moisture and particles: Moisture in the air enables microbes to
"hide," decreasing their exposure. Humidity higher than 70 percent can
diminish purifier effectiveness.
?	Design: Single "stick-style" purifiers in ductwork are effective at
inhibiting microbial growth inside the duct, but are not effective at
sterilizing the air.

?	Maintenance: Bulbs should be cleaned periodically to remove dust
that reduces light intensity. Bulbs also lose the ultraviolet portion
of the light spectrum with age. Replace bulbs according to
manufacturers' recommendations.
?	Operation time. UV air purifiers only work when the light source is
on and air is moving past the bulb. For maximum effectiveness, the
furnace air-handler should operate continuously. While this provides
better air purification than intermittent operation, it uses more
electricity. UV light deteriorates many plastics and some metals.
Shield UV light sources inside heating systems from plastics and
susceptible metals.

While UV air purifiers will oxidize some organic material in the air,
they will not remove all particulates. Since many allergies are
related to the particles in the air, any "whole-house" air
purification strategy should also include a high-efficiency filter.?

??  Micro-organisms, including bacteria, viruses, and algae, are
inactivated within seconds of UV light disinfection, but all are not
equally sensitive. Generally, viruses and algae are more resistant to
disinfection by UV light.
?  UV light is effective in inactivating Cryptosporidium, while at the
same time decreasing chlorinated disinfection by-products.
?  UV disinfection is used in air and water purification, sewage
treatment, protection of food and beverages, and many other
disinfection and sterilization processes.?

   ?An air cleaner is required to filter the air in a given space a
prescribed number of times each hour to maintain a satisfactory level
of cleanliness. The number of air changes required to attain a level
of cleanliness has a limit. To be collected at the air cleaner,
particles cannot be removed from the air in a room any faster than
they mix with the air. To go beyond 15 air changes per hour may not
increase the effectiveness of the air cleaning system. In addition, a
higher number of air changes create drafts, causing discomfort to the
occupants of the room.?

?	?Units should not be placed near HVAC system intakes or outlet
grills where conflicting airflows could inhibit the performance of
both systems.
?	Multiple units should be placed so that they are "balanced" in the room.
?	Equipment in the room must be located so that fixtures do not block
or divert the air pattern.
?	Clearance for doors must always be provided so equipment can be serviced. 
?	The objective is to create a continuous air pattern throughout the
room so that air can be properly re-circulated.
The most common triggers in addition to tobacco smoke odors include:
?	Formaldehyde from pressed-wood products
?	Organics from building materials, carpets and office furnishings
?	Chemicals found in materials, fragrances and disinfectants
?	Wall coverings and adhesives
?	Paints
?	Copying machines and office supplies
?	Dirty ventilation systems
?	Water-damaged walls, ceilings and carpets
?	Pesticides from pest management practices

?While the present investigation indicated that concentrations of
fungi were significantly lower when UV lamps were in use, the study
did not show what stages of fungal growth were most susceptible, nor
did it show whether there was a reduction in spore viability. Also, we
were not able to show if all the fungi obtained from the AHUs were
susceptible to the UV light. In addition, this study was limited to
the species found in the building investigated. Asthana and Tuveson
(2) showed that germicidal effects were highly selective for certain
species. Clearly, more work is needed to determine the direct effects
of UV-C radiation on fungi capable of growing in HVAC systems.?

?A good uv air purifier has such a UV spectrum that it minimizes or
eliminates ozone formation (very low intensity at 185 nm
ozone-producing wave length), while having high intensity at around
254 nm wavelength, which stimulates hydroxyl production for effective
air cleaning.

The effectiveness of an ultraviolet air purifier depends on the
intensity (wattage) of the UV light and the time of exposure to the
light. So, you typically need quite a high wattage UV lamp, especially
in case of fast air flow.
A UV air purifier does not need any replacement filters (filterless
technology), unless it is combined with air filter parts. Yet, you may
need to pay attention to the UV lamp. It loses its intensity every
year of operation (like 15 percent per year), and should be replaced
time after time (depends on the UV lamp quality.)?

?UV doses required for bacterial and viral inactivation are relatively
low, typically in the range of 2 to 6 mW-s/cm2 for 1 log

You may be right about producing mutant forms-at least for some
species of organisms. However, sterilizing bacteria means it can't
reproduce, and will die without progeny!
?The lab that follows helps to illustrate the operation of natural
selection with a particular strain of bacteria, Escherichia coli (E.
coli), that is exposed to ultraviolet radiation. Most E. coli are
sensitive to ultraviolet (UV) light and die. UV light has a particular
wavelength that can be absorbed by the genetic material, the DNA
molecules, causing physical damage and inactivation of the various
cellular (chemical) activities controlled by the DNA. However, some
bacteria can survive the exposure to UV, depending on exposure time,
because of mutations already present in their DNA. These resistant
strains can pass along the genetic survival mechanism when they
reproduce, by fission. You will be able to identify the surviving
bacteria and transfer them to new growth environments. The progeny
from the survivors will also be tested to see which bacteria inherited
the ability to flourish when exposed to UV light. Reproduction in
bacteria can occur in 20 minutes or so, and resistant colonies can be
apparent over a 24-hour period.?

?Halophilic Archaea are much more resistant to ultraviolet (UV) light
damage than Escherichia coli and other species of Bacteria. This
resistance is probably due, at least in part, to the large number of
genes present in the genome that are involved in DNA repair. It has
been shown that halophilic genomes often contain some repair genes
homologous to those in prokaryotes and other genes homologous to
repair genes found in eukaryotes?

Alternatives to UV light air cleaners -

    ?We discovered that the Asthma and Allergy Foundation of America
(AAFA), a nonprofit patient organization dedicated to improving
quality of life for asthma and allergy sufferers, has awarded its
Label of Truth to the Ionic Breeze. We contacted William McLin, the
Executive Director of AAFA, who stated that though this is not a seal
of endorsement, it does mean that AAFA's Medical-Scientific Council
(volunteer MDs, PhDs, MPHs, and other experts) examined the research
behind Sharper Image's claims and deemed the claims to be true. AAFA
would not release their research findings to us, but instead referred
us back to The Sharper Image. The British Allergy Foundation has also
given the Ionic Breeze its Seal of Approval. After performing
independent testing, they found "the Ionic Breeze reduces the allergen
load in the air sufficiently to be of benefit to allergy sufferers."
The details of this testing were not made available to us.?

Reviews of other air cleaners-

  Ionic air purifiers were found to actually harm asthmatics from
their production of ozone. The newest version of the Ionic Breeze
recommended now is this one, with an ozone guard.

This previous answer ay interest you:

HEPA air filtering systems are rated highly:

Treatment Tools for asthma

?	?Allergic triggers: If you come into contact with substances in your
bedroom that cause an allergic reaction, such as cat or dog dander and
dust, they may be responsible. Irritating fumes from kerosene heaters
and wood-burning stoves may also cause an asthma attack. Exposure to
these or other triggers from earlier in the day may also cause a
delayed reaction with asthma symptoms appearing during the night.
?	Hormones: Levels of hormones in the body also change throughout the
day. In people with asthma, the changing levels of hormones during the
night may predispose the muscles in the lungs to contract, resulting
in narrowing and inflammation of the bronchi.
?	Stomach acid reflux: If you notice a burning in your lower chest
area or a bitter taste in your mouth when you awake in the morning,
you may have stomach acid reflux.

   Anecdotally, I have seen fewer asthma symptoms in myself, simply by
changing my pillowcase each night! (I started this practice for
rosacea, but noticed an effect on my breathing!)  Mites and dust are
known asthma triggers.,14477.asp
?Molds may form on foam pillows when you perspire. To prevent mold,
put the pillow in an airtight cover and tape the cover shut. Wash the
pillow every week, and make sure to change it every year.
Molds also form in house plants, so check them often. You may have to
keep all plants outdoors.?

??  Reduce or remove as many asthma and allergy triggers from your
home as possible.
?  If possible, use air filters and air conditioners to make your home
cleaner and more comfortable.
?  Pay attention to the problem of dust mites. Work hard to control
this problem in the bedroom.?

I hope this has helped you select a good air purifier. Keeping your
house as dust free as possible will help considerably, if dust is a
trigger for you.

Please do not rate this answer untill you are satisfied. If you need
further assistance, simply ask for an Answer Clarification, and allow
me to respond. i will be happy to help further, on this question,
before you rate.

Regards, Crabcakes

Search Terms
UV + air quality + asthma + effectiveness
UV Air cleaners + efficacy
UV light + mutant + organisms
effective air purifiers + asthma
home air filters + reviews
UV + air purifier + reviews
UV air cleaners + reviews
HEPA air purifiers + reviews

Request for Answer Clarification by seekeroftruth2-ga on 31 Jan 2006 08:18 PST
Thank you for your detailed response.  We live in a world where
bacteria are rapidly becoming resistant to the antibiotics developed
to fight them.  They do this with only their natural ability to
mutate.  I hate to add to their natural ability by subjecting them to
uv radiation as they pass through the furnace.  If we keep the furnace
fan running 24 hours a day, then bacteria and other living pathogens
will be subject to brief, one or two second passes through the
furnance and the uv light.  If we keep it on auto, then some bacteria
and living pathogens will have hours of light exposure, and others
only a second or two.  Could you please give me more clarification
regarding this?  Have any safety studies been done on bacteria and
other living pathogens that would replicate a home furnace situation?

Clarification of Answer by crabcakes-ga on 31 Jan 2006 20:09 PST
Hi Seekeroftruth,

   I have seen your clarification, and I will respond ASAP - it will
probably be late afternoon or early evening tomorrow. I am immersed in
another project now. Will this be acceptable? Thanks so much for your

   Regards, Crabcakes

Request for Answer Clarification by seekeroftruth2-ga on 01 Feb 2006 17:46 PST
That would be fine.  Thank you.

Clarification of Answer by crabcakes-ga on 01 Feb 2006 20:36 PST
Hi Seekeroftruth,

  I'm not sure how some bacteris/organisms will be exposed to "hours" of light.

In any case, I found

"The ultraviolet component of sunlight is the main reason microbes die
in the outdoor air. The die-off rate in the outdoors varies from one
pathogen to another, but can be anywhere from a few seconds to a few
minutes for a 90-99% kill of viruses or contagious bacteria. Spores,
and some environmental bacteria, tend to be resistant and can survive
much longer exposures. UVGI systems typically use much more
concentrated levels of ultraviolet energy than are found in sunlight.

Some properly designed, and well-maintained, UVGI installations have
proven highly effective, as in certain hospitals, and some studies
perfomed in schools. CDC guidelines recommend the use of UVGI only
with the simultaneous use of HEPA filters and high rates of purge
airflow. The germicidal effects can also be species-dependent."

"633 nm laser irradiation has been investigated. In all the cases,
irradiation has lethal and mutagenic effects on bacteria, and all the
mutagenic curves are of a similar form: in the region of small
irradiation doses a peak of mutation frequency is observed, further
the curve is reduced and again increases at greater irradiation doses.
Taking into account that non-irradiated E.coli bacteria cells are
capable of filament formation, we can suppose that the mutation
frequency curve consists of two components: component of more
sensitive filaments"

UV radiation's effect on spores:

"It is important for organisms to maintain their genomic integrity.
However, they are continuously exposed to various DNA-damaging agents
such as UV light, ionizing radiation and chemicals. Organisms
therefore have mechanisms by which DNA damage is identified and

I have found no studies of furnace UV air cleaners and the effect on
pathoogenic utations. Let me remind you that the sources I post are
reliable sources and not from sites that market air purifiers.
Honestly, there are so many variables, I doubt if there are any
precise studies. The variables consist of types of organisms, where in
the air the organisms are (high/low), the concentration of organisms
in the air, what capacity of air exchange your furnace blower is
capable of, size of the light, etc.

I hope the additional information I have provided helps you understand
the complexity of this question (mutation of DNA). Let me again remind
you that airborne organisms are not the primary cause of asthma, and
that dust, dander, fumes, smoke and such are, and are not removed by
UV light.

Good Luck! 
Sincerely, Crabcakes

Request for Answer Clarification by seekeroftruth2-ga on 02 Feb 2006 08:59 PST
Your information has been very helpful.  To clarify, my husband wants
a uv light in our furnace, and I do not.  He actually installed one,
and I took it out.  I studied genetics, physiology, and oncology in
college, and my gut tells me a uv light in a home furnace is a bad
idea, but I need the research to back up my gut feeling.  Thank you
for your help and information.

Clarification of Answer by crabcakes-ga on 02 Feb 2006 17:46 PST
Hello Seeker,

    I'm glad the answer was useful. I took quite a bit of microbiology
in college, and I remember that in order for bacteria to multiply,
they need precise nutrients aand a certain temperature range.
Pathogenic bacteria that may be airborne are unlikely to reproduce.
They happen to be there, but there is no food source for them. Viruses
need a host, so it's unlikely the presence of airborne viruses will
reproduce either. The numbers of airborne pathogens in a home are low
in numbers, if present at all, unless there is standing water in the
home, or conditions that provide a breeding ground for organisms.

    Sincerely, Crabcakes
seekeroftruth2-ga rated this answer:4 out of 5 stars
I received a lot of useful information.

Subject: Re: Effect of ultraviolet light on pathogens and human health consequences
From: mikewa-ga on 31 Jan 2006 04:44 PST
With respect for pour concern about the UV producing dangerous
mutations, you can rest easy. It is true that UV light does cause
mutations, but the probability that  this will be a danger is
extremely low. First, the UV dose is adjusted to be lethal, so few
microbes will survive. Those that do survive may have new mutations
but the vast majority of these will decrease the microbe's likelyhood
of survival. You might find a good quality HEPA filter a better
solution, since it will remove all particles, both living and dead.
Subject: Re: Effect of ultraviolet light on pathogens and human health consequences
From: magnesium-ga on 02 Feb 2006 11:24 PST
The likelihood that UV light will produce any significant number of
viable mutations is negligible.
Subject: Re: Effect of ultraviolet light on pathogens and human health consequences
From: seekeroftruth2-ga on 02 Feb 2006 17:15 PST
Bacteria are already famous for their ability to mutate.  That is why
there are resistant infections and flesh eating bacteria.  I really
don't want to help bacteria (or any other pathogens) with that process
inside my furnace.  It is not a closed system, and I don't have the
ability to control the amount of uv radiation or the exposure time. 
However, if you have any research studies that address these issues, I
would be welcome the opportunity to read them.
Subject: Re: Effect of ultraviolet light on pathogens and human health consequences
From: mikewa-ga on 03 Feb 2006 09:51 PST
I get the feeling you have already made up your mind, and simply want
someone to agreee with you. However, the killing effect of the UV will
more than offset the increase in harmful mutations: many microbiology
labs have UV lights than come on when the room is empty and the net
effect is reduced infection.
Subject: Re: Effect of ultraviolet light on pathogens and human health consequences
From: seekeroftruth2-ga on 03 Feb 2006 14:26 PST
You are partially correct.  I have made up my mind.  But I would like
to see some research studies to prove me wrong.

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