Re: efficacy of germicidal UV

[Guest guest]

,

I posted this when the study came out:

In a recent paper, “Effect of ultraviolet germicidal lights in office

ventilation systems on workers’ health and well-being: double-blind multiple

crossover trial,” (Lancet 2003; 362: 1785-91), the authors Menzies et.al.

concluded that “installation of UVGI in most North American offices could

resolve work-related symptoms in about 4 million employees, caused by

microbial contamination of the heating, ventilation and air-conditioning

systems.”

Despite the fact that ultraviolet germicidal irradiation (UVGI) has been

shown in many previous studies to reduce airborne contagion, I believe that

the conclusion of this study overstates the impact of UVGI on HVAC systems

and office indoor air quality.

Three healthy, well-ventilated (peak values of carbon dioxide were under 620

ppm) office buildings in Montreal, Canada were evaluated over the course of

one year (July 1999 to July 2000). In the study, UV lamps (245-266 nm

wavelength band), rated at 450 mW/cm2 at a distance of one meter, were

mounted with reflectors 15 to 74 cm from the cooling coils and drip pans. At

this level of irradiation (greater than what is typical), the authors

estimated that the survival time for resistant organisms would be less than

4 minutes. Within the HVAC system, the UVGI lamps were cycled, operating for

12 weeks off, and then 4 consecutive weeks on. Questionnaires were

repeatedly distributed to about 800 office workers to obtain subjective

opinions regarding environmental satisfaction and allergy symptoms

(categories included systemic, mucosal, respiratory, musculo-skeletal, and

“any symptom”) during the different time intervals.

The concentration of microbes on the coils and in the drip pans was

determined by placing sterile 5 cm x 5 cm “coupons” of sheet metal on the

surfaces (exposed directly to the UVGI), and then placing the exposed

coupons on a Petri dish containing culture media (Sabouraud or MEA), and

incubating the dishes. Coupons (receiving no UVGI) were also placed on the

filters. Air samples indoors and outdoors were obtained with Burkard

volumetric air samplers (with Petri dishes) to determine the concentration

of fungal spores. A total of 1240 samples were assayed.

Endotoxin concentrations were determined using volumetric sampling and

polycarbonate filter cassettes for the air, and by washings directly from

the dust impacted on the coupon surfaces. A total of 284 samples were

assayed. Airborne endotoxin was not detectable at workstations with the UVGI

either on or off and there was a slight increase in levels on the filter

coupons with the UVGI on. The amount of endotoxin on the coil coupon dropped

from 8 endotoxin units (EU) to zero with the UVGI on.

Culturable air samples for fungal spores at both the returns and supplies,

with the UVGI both on and off, were 0 (zero) cfu/m3. The number of

culturable spores per 25 cm2 on all coupons was very low, and averaged at

the cooling coil from 0 (UVGI on) to about 4 (UVGI off) or far less than one

spore per cm2 after a 4- or 12-week exposure period. The coupons on the

filters collected 3 cfu/coupon (UVGI off) and 2 cfu/coupon (UVGI on). The

coupons may not have been very efficient collectors since they lacked a

“sticky” coating and were positioned perpendicular to the air flows and thus

obstructed the stream lines. In addition, the irradiated coupons were

exposed directly to the UVGI, whereas microbes on an actual HVAC surface

would have received incident light at a variety of angles, the intensity of

which would be attenuated by the dust accumulations.

The data and results for different seasons were not separated. Since in

Montreal there is a long heating season and a short cooling season, the

expected results for each season should be quite different. In addition,

during the heating season there is no condensation of moisture to promote

microbial growth. In fact, in the presence of minimal dust on the coupons

and few organisms, and without moisture, there is little opportunity for any

microbial amplification, either in the heating or cooling season.

Despite the reported reduction in symptoms indoors at work during the

UVGI-on periods, no statistically significant differences were reported in

the indoor air concentrations of microbes at work stations; thus the authors

were left with no explanation for the reported reduction in symptoms

associated with UVGI. (The authors postulated that the UVGI radiation may

have somehow reduced the aerosolization of microbial antigenic proteins.)

To prevent microbial growth due to moisture or high relative humidity in

HVAC systems, the most important components of hygiene will always be proper

design to begin with, adequate filtration (a minimum of MERV 6-8), and

regular maintenance. Though UVGI may certainly serve as an adjunct in

disinfecting exposed air and reducing microbial growth on irradiated

surfaces, the impact on overall indoor air quality of UVGI alone should not

be overstated.

C. May

May Indoor Air Investigations LLC

1522 Cambridge Street

Cambridge, MA 02139

www.mayindoorair.com

www.myhouseiskillingme.com

iamnotanairhead writes:

> Hi all,

>

> Not too long ago, AirwaysEnv@... wrote:

>

>>Unfortunately, science and scientists do not exist outside of

>> economics and finance. It can be seen in the way new technologies

>>are marketed today that the line between science and marketing gets

>> fuzzier and fuzzier. How about all these pharmaceutical

>> advertisements on television today? Or ozone generating air

>> purifiers. Or the science behind UV light bulbs in ducts to kill

>>mold spores whizzing by...

>

> I thought that the science behind germicidal UV was sound. Anyone have

> any thoughts on the matter?

>

> Thanks,

>

[Guest guest]

,

You have to read the words several times to catch the drift of what is being said.

I support your belief in the efficacy of germicidal UV.

To prove the concept just do a web search of <UV hospital McGill>

What you were reading was a slam at the misuse of good science by inexperienced engineer types who claim germicidal UV will kill all the bad bugs. It doesn't! It only can kill what passes close enough to its killing field to be fatally irradiated. It does however do wonders for the HVAC trade when it installed close enough before the cooling coils to inhibit normal mold growth that robs a cooling system of its efficiency.

But as far as killing the germs that make people sick there is a good bit of engineering needed before a germicidal UV system can be deemed reliable. However recent science has greatly enhanced the efficiency of UV bulbs for germicidal use by providing a target of titanium oxide so air passing by will literally be transformed into a fume of hydro peroxide and hydroxyl radicals which quickly attach themselves to bacteria, viruses and mold spores in such a way to defeat the cell wall so the cells either dies or loses the ability to reproduce. The process can be easily reviewed by doing a web search using various combinations of the following keywords: photocatalytic, photocatalysis, hospital, bacteria. You'll find many good scientific hits along with a few pushy promotions.

Be well.

Gibala

=====================================

efficacy of germicidal UV

Hi all,Not too long ago, AirwaysEnv@... wrote:>Unfortunately, science and scientists do not exist outside of > economics and finance. It can be seen in the way new technologies >are marketed today that the line between science and marketing gets > fuzzier and fuzzier. How about all these pharmaceutical > advertisements on television today? Or ozone generating air > purifiers. Or the science behind UV light bulbs in ducts to kill >mold spores whizzing by...I thought that the science behind germicidal UV was sound. Anyone have any thoughts on the matter?Thanks,

[Guest guest]

:

I, for one, believe the science behind UV irradiation as a germicidal method

is very sound. I have seen (by my measurements) a tremendous reduction in

active colony forming units inside HVAC systems (e.g., duct work, heat

exchangers, fan blades, etc.) when UV lamps are installed. There was one

negative comment recently about " UV killing spores whizzing by. " I for one

believe it does work, although, like any engineering control, there are

limitations. If the air speed (velocity) is really high and the UV lamp

energy is low, there is a significant reduction in effect. If poorly

designed/installed, the benefits of UV irradiation can be negligible. The

lamps I have installed in HVAC systems are REALLY strong and warrant LOTO

controls so they are not energized when the HVAC system is worked on, or if

filters are changed. Moreover, they are shielded on the upstream side so

debris/particulates do not impact and soil the bulbs. I usually place the

lamps 4 to 6 inches from the heat exchanger (HE) on the upwind side, and

rarely am I installing less than three lamps. I don't like placing them in

dirty HVAC systems and when I install them on a retrofit, it is after the

system is thoroughly cleaned. In side by side comparisons, i.e., HEs with

lamps versus HEs without lamps, the cleanliness of the HEs with lamps could

be easily seen one year later. In fact, the HEs (with lamps) looked as

clean as the day the lamps were installed, while the other HEs had visible

dirt on them. There is a lot to designing and installing UV systems in HVAC

systems to make them effective - it is NOT a plug-n-play control. I know

Kaiser Permanente has invested heavily in UV irradiation of their HVAC

systems in an effort to control infection. I believe their results are

really supportive of UV irradiation. A big advantage of UV irradiation is

the low cost to operate. A big disadvantage is the high cost of each (good

quality) bulb, and several bulbs are needed in each fan unit on small

package units. On buildings with a centralized HVAC system (versus

individual roof-mounted package units) there could be 20 to 30 bulbs, or

more. Moreover, the HVAC fan unit must be so located that is can be easily

serviced (not a problem with centralized HVAC systems). This is not the

case in most residential construction because most architects/contractors

design and place the fan unit in the attic...a very convenient but really

dumb place to put a piece of machinery that needs periodic service with

filters that warrant frequent replacing.

If I had a house that had central air (I don't, we open windows) I would

install UV irradiation along with an appropriate, well-sealed, HPFF filter

bank; and it would deliver the cleanest air at the best, and lowest,

operating cost. I am a believer in UV.

For what it is worth...

--

Geyer, PE, CIH, CSP

President

KENTEC Industries, Inc.

Bakersfield, California

www.kerntecindustries.com

> Hi all,

>

> Not too long ago, AirwaysEnv@... wrote:

>

>> Unfortunately, science and scientists do not exist outside of

>> economics and finance. It can be seen in the way new technologies

>> are marketed today that the line between science and marketing gets

>> fuzzier and fuzzier. How about all these pharmaceutical

>> advertisements on television today? Or ozone generating air

>> purifiers. Or the science behind UV light bulbs in ducts to kill

>> mold spores whizzing by...

>

> I thought that the science behind germicidal UV was sound. Anyone have

> any thoughts on the matter?

>

> Thanks,

>

>

>

>

>

>

>

>

>

>

> FAIR USE NOTICE:

>

> This site contains copyrighted material the use of which has not always been

> specifically authorized by the copyright owner. We are making such material

> available in our efforts to advance understanding of environmental, political,

> human rights, economic, democracy, scientific, and social justice issues, etc.

> We believe this constitutes a 'fair use' of any such copyrighted material as

> provided for in section 107 of the US Copyright Law. In accordance with Title

> 17 U.S.C. Section 107, the material on this site is distributed without profit

> to those who have expressed a prior interest in receiving the included

> information for research and educational purposes. For more information go to:

> http://www.law.cornell.edu/uscode/17/107.shtml. If you wish to use copyrighted

> material from this site for purposes of your own that go beyond 'fair use',

> you must obtain permission from the copyright owner.

>

[Guest guest]

Mike,

I am not arguing that UV isn't germicidal, but without a clean system to

begin with, and efficient filtration (minimum MERV 6-8, preferably MERV 11)

in place to keep the linings and coil clean, UV is worthless.

And few installers take the care that you seem to; based on the

installations I've seen, most just pop a lamp in someplace and walk off with

the exorbitant fee.

For the money, I'd spend on cleaning and filtration before UV irradiation.

C. May

May Indoor Air Investigations LLC

1522 Cambridge Street

Cambridge, MA 02139

www.mayindoorair.com

www.myhouseiskillingme.com

Geyer writes:

> :

>

> I, for one, believe the science behind UV irradiation as a germicidal method

> is very sound. I have seen (by my measurements) a tremendous reduction in

> active colony forming units inside HVAC systems (e.g., duct work, heat

> exchangers, fan blades, etc.) when UV lamps are installed. There was one

> negative comment recently about " UV killing spores whizzing by. " I for one

> believe it does work, although, like any engineering control, there are

> limitations. If the air speed (velocity) is really high and the UV lamp

> energy is low, there is a significant reduction in effect. If poorly

> designed/installed, the benefits of UV irradiation can be negligible. The

> lamps I have installed in HVAC systems are REALLY strong and warrant LOTO

> controls so they are not energized when the HVAC system is worked on, or if

> filters are changed. Moreover, they are shielded on the upstream side so

> debris/particulates do not impact and soil the bulbs. I usually place the

> lamps 4 to 6 inches from the heat exchanger (HE) on the upwind side, and

> rarely am I installing less than three lamps. I don't like placing them in

> dirty HVAC systems and when I install them on a retrofit, it is after the

> system is thoroughly cleaned. In side by side comparisons, i.e., HEs with

> lamps versus HEs without lamps, the cleanliness of the HEs with lamps could

> be easily seen one year later. In fact, the HEs (with lamps) looked as

> clean as the day the lamps were installed, while the other HEs had visible

> dirt on them. There is a lot to designing and installing UV systems in HVAC

> systems to make them effective - it is NOT a plug-n-play control. I know

> Kaiser Permanente has invested heavily in UV irradiation of their HVAC

> systems in an effort to control infection. I believe their results are

> really supportive of UV irradiation. A big advantage of UV irradiation is

> the low cost to operate. A big disadvantage is the high cost of each (good

> quality) bulb, and several bulbs are needed in each fan unit on small

> package units. On buildings with a centralized HVAC system (versus

> individual roof-mounted package units) there could be 20 to 30 bulbs, or

> more. Moreover, the HVAC fan unit must be so located that is can be easily

> serviced (not a problem with centralized HVAC systems). This is not the

> case in most residential construction because most architects/contractors

> design and place the fan unit in the attic...a very convenient but really

> dumb place to put a piece of machinery that needs periodic service with

> filters that warrant frequent replacing.

>

> If I had a house that had central air (I don't, we open windows) I would

> install UV irradiation along with an appropriate, well-sealed, HPFF filter

> bank; and it would deliver the cleanest air at the best, and lowest,

> operating cost. I am a believer in UV.

>

> For what it is worth...

> --

> Geyer, PE, CIH, CSP

> President

> KENTEC Industries, Inc.

> Bakersfield, California

> www.kerntecindustries.com

>

>

>

>

>

>

>

>> Hi all,

>>

>> Not too long ago, AirwaysEnv@... wrote:

>>

>>> Unfortunately, science and scientists do not exist outside of

>>> economics and finance. It can be seen in the way new technologies

>>> are marketed today that the line between science and marketing gets

>>> fuzzier and fuzzier. How about all these pharmaceutical

>>> advertisements on television today? Or ozone generating air

>>> purifiers. Or the science behind UV light bulbs in ducts to kill

>>> mold spores whizzing by...

>>

>> I thought that the science behind germicidal UV was sound. Anyone have

>> any thoughts on the matter?

>>

>> Thanks,

>>

[Guest guest]

There was one negative comment recently about "UV killing spores whizzing by." I for one believe it does work, although, like any engineering control, there are

limitations. If the air speed (velocity) is really high and the UV lamp

energy is low, there is a significant reduction in effect. If poorly

designed/installed, the benefits of UV irradiation can be negligible.

Question: Why doesn't UV from the sun kill mold spores floating around outdoors on a bright, sunny day? I've had some very high outdoor counts in sunny, summer weather.

Steve Temes

[Guest guest]

1. I took a quick look at outdoor today (very sunny) with a radiometer.

Vis Light (>400 to 700 nm wavelength) >200 foot-candles

UVB (315-385 nm) 40 uW/cm2

UVC (<285 nm) 40 uW/cm2

2. I do recall an article on diurnal (night/day) variations in mold viability

with UV as cited causation. Other major factor dark (Demitiaceous) vs clear

(hyaline). This last part or dark vs light can also be seen in differences

between inside and outside mold species with regard to survivability and

frequency of occurrence (dark better outside and clear inside).

Tony

...........................................................................

" Tony " Havics, CHMM, CIH, PE

pH2, LLC

PO Box 34140

Indianapolis, IN 46234

cell

90% of Risk Management is knowing where to place the decimal point...any

consultant can give you the other 10%â„ 

This message is from pH2. This message and any attachments may contain legally

privileged or confidential information, and are intended only for the individual

or entity identified above as the addressee. If you are not the addressee, or if

this message has been addressed to you in error, you are not authorized to read,

copy, or distribute this message and any attachments, and we ask that you please

delete this message and attachments (including all copies) and notify the sender

by return e-mail or by phone at . Delivery of this message and any

attachments to any person other than the intended recipient(s) is not intended

in any way to waive confidentiality or a privilege. All personal messages

express views only of the sender, which are not to be attributed to pH2 and may

not be copied or distributed without this statement.

Re: efficacy of germicidal UV

Steve,

It is the intensity of the UV that kills the bacteria and mold. I don't

recall the exact numbers but UV biosafety hood lights are about 100 or

more times more intense than sun light.

Bob

FAIR USE NOTICE:

This site contains copyrighted material the use of which has not always been

specifically authorized by the copyright owner. We are making such material

available in our efforts to advance understanding of environmental, political,

human rights, economic, democracy, scientific, and social justice issues, etc.

We believe this constitutes a 'fair use' of any such copyrighted material as

provided for in section 107 of the US Copyright Law. In accordance with Title 17

U.S.C. Section 107, the material on this site is distributed without profit to

those who have expressed a prior interest in receiving the included information

for research and educational purposes. For more information go to:

http://www.law.cornell.edu/uscode/17/107.shtml. If you wish to use copyrighted

material from this site for purposes of your own that go beyond 'fair use', you

must obtain permission from the copyright owner.

[Guest guest]

Mike,

You are doing it right. It is extremely rare to find mold on a filter

(compared to finding it on the coil or lining) so why bother to kill the

biomass. It's much more important to keep the bulb clean.

C. May

May Indoor Air Investigations LLC

1522 Cambridge Street

Cambridge, MA 02139

www.mayindoorair.com

www.myhouseiskillingme.com

Geyer writes:

> Curtis:

>

> Most filter media will break down with as little as 20 to 40 hours of

> direct, high-intensity UV irradiation. I always install UV lamps downstream

> of the filter fabric ­ this also helps keep the bulbs cleaner. Though I

> have heard the arguments for placing UV bulbs upstream of the filter fabric

> to kill the trapped boimass, I feel this is a mistake because few filter

> fabrics will maintain filtration efficiency when exposed to the UV energy;

> albeit, I imagine weak UV bulbs will have little effect on the fabric, they

> will also have little effect on the biomass.

>

> --

> Geyer, PE, CIH, CSP

> President

> KENTEC Industries, Inc.

> Bakersfield, California

> www.kerntecindustries.com

>

[Guest guest]

Matt, Slight correction: D = I · t D = UV Dose, mW×s/cm2 I = Intensity, mW/cm2 t = Exposure time, s http://www.epa.gov/OGWDW/mdbp/word/alter/chapt_8.doc "Research indicates that when microorganisms are exposed to UV radiation, a constant fraction of the living population is inactivated during each progressive increment in time. This dose-response relationship for germicidal effect indicates that high intensity UV energy over a short period of time would provide the same kill as a lower intensity UV energy at a proportionally longer period of time." Outdoor spores should have long exposure time of several hours... Wei Tang QLAB Matt Klein wrote: It is the intensity of the UV that kills the bacteria and mold. I don't recall the exact numbers but UV biosafety hood lights are about 100 or more times more intense than sun light.Bob, I have to make a slight correction here. The dose is the poison. Intensity is just part of that equation. For UV, dose = intensity + exposure time with the correct wavelength for the biologicals of interest. For a kill, biologicals on surfaces can be exposed to lower intensity light because they can be exposed for a much longer time than those floating through the light in an air stream. The latter require much more intense light because exposure time is so short. Note that I know I am presenting the simplistic picture. Other factors, such as moisture and dust concentrations

can impact exposure. ******************************************************If what is written looks too stupid to be written by me, I disclaim it. Onthe other hand, if it is brilliant, then I have no one to blame but myself. Otherwise, whether you choose to accept my opinion is up to you.****************************************************** K. Klein, PE ME, MBAIndoor Air Quality Solutions, Inc.2523 SR 133Bethel, OH 45106-0007VOICE: FAX: (with notice)E-mail: mkklein68@...*******************************************************Wouldn't it be nice if common sense were really common? Wei Tang, Ph.D.Lab DirectorQLABCherry Hill, NJ

[Guest guest]

Matt,

You are correct. It is the dose that is the critical item.

However, with UV, most species, including humans have adjusted to a

background level of radiation. Either the cells repair the damage or

their DNA is immune.

This level of UV (was?) in the normal range in the environment. Now

with the loss of the ozone layer, UV radiation is at least 10-15%

higher and much higher in some places.

I know that there is some reported skin(sun) burn affected reported in

southern argentina and chile. However, the effect on soil microbes and

on arctic microbes has not been reported that I am aware of.

So in order for UV to cause sufficient DNA damage to render mold spores

or bacteria non viable, a minimum intensity is necessary.

There is also the UV A verses UV B issue.

On a humorous note, In the movies, one sees people being exposed to UV

to sterilize their skin from outer space microbes. The amount of UV

necessary to kill microbes from out space, would also kill the

people.-post toasties.

Bob

[Guest guest]

"Outdoor spores should have long exposure time of several hours... "or several minutes if they were just released, or several days if they have been floating around, depending which spores in the air you are referring to. There should be a mixture of them unless it's right after rainfall, which washs away most of them. The sproes released after that should be more uniform. The UV lamp in HVAC would be providing additional dosage on top of the dosage from sunlight for spores from outdoors. D = (I(sun) x T(sun)) + (I(lamp) x T (lamp)) Wei Tang QLAB Wei Tang wrote: Matt, Slight correction: D = I · t D = UV Dose, mW×s/cm2 I = Intensity, mW/cm2 t = Exposure time, s http://www.epa.gov/OGWDW/mdbp/word/alter/chapt_8.doc "Research indicates that when microorganisms are exposed to UV radiation, a constant fraction of the living population is inactivated during each progressive increment in time. This dose-response relationship for germicidal effect indicates that high intensity UV energy over a short period of time would provide the same kill as a lower intensity UV energy at a proportionally longer period of time." Outdoor spores should have long exposure time of several hours... Wei Tang QLAB Matt Klein wrote: It is the intensity of the UV that kills the bacteria and mold. I don't recall the exact numbers but UV biosafety hood lights are about 100 or more times more intense than sun light.Bob, I have to make a slight correction here. The dose is the poison. Intensity is just part of that equation. For UV, dose = intensity + exposure time with the correct wavelength for the biologicals of interest. For a kill, biologicals on surfaces can be exposed to lower intensity light because they can be exposed for a much longer time than those floating through the light in an air stream. The latter require much more intense light because exposure time is so short. Note that I know I am presenting the simplistic picture. Other factors, such as moisture and dust concentrations can impact exposure. ******************************************************If what is written looks too stupid to be written by me, I disclaim it. Onthe other hand, if it is brilliant, then I have no one to blame but myself. Otherwise, whether you choose to accept my opinion is up to you.****************************************************** K. Klein, PE ME, MBAIndoor Air Quality Solutions, Inc.2523 SR 133Bethel, OH 45106-0007VOICE: FAX: (with notice)E-mail: mkklein68@...*******************************************************Wouldn't it be nice if common sense were really common? Wei Tang, Ph.D.Lab DirectorQLABCherry Hill, NJWei Tang, Ph.D.Lab DirectorQLABCherry Hill, NJ