RE: Re: efficacy of germicidal UV

[Guest guest]

Interesting.See comments below plus: UV exposure should be down around 1 mW/cm2 (see ACGIH TLV on UV by wavelength)

Tony.......................................................................... "Tony" Havics, CHMM, CIH, PEpH2, LLCPO Box 34140Indianapolis, IN 46234 cell90% 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.-----Original Message-----From: iequality [mailto:iequality ] On Behalf Of Jeff MaySent: Friday, April 07, 2006 6:54 PMTo: iequality Subject: Re: efficacy of germicidal UV,I posted this when the study came out:In a recent paper, “Effect of ultraviolet germicidal lights in officeventilation systems on workers’ health and well-being: double-blind multiplecrossover trial,†(Lancet 2003; 362: 1785-91), the authors Menzies et.al.concluded that “installation of UVGI in most North American offices couldresolve work-related symptoms in about 4 million employees, caused bymicrobial contamination of the heating, ventilation and air-conditioningsystems.â€Despite the fact that ultraviolet germicidal irradiation (UVGI) has beenshown in many previous studies to reduce airborne contagion, I believe thatthe conclusion of this study overstates the impact of UVGI on HVAC systemsand office indoor air quality. (Agree)Three healthy, well-ventilated (peak values of carbon dioxide were under 620ppm) office buildings in Montreal, Canada were evaluated over the course ofone year (July 1999 to July 2000). In the study, UV lamps (245-266 nmwavelength band), rated at 450 mW/cm2 at a distance of one meter, weremounted with reflectors 15 to 74 cm from the cooling coils and drip pans. Atthis level of irradiation (greater than what is typical - no kidding - Hart , back in 1942 noted that a kill rate of >99% at 3 min for 30 mW/cm2 at the surface), the authorsestimated that the survival time for resistant organisms would be less than4 minutes. Within the HVAC system, the UVGI lamps were cycled, operating for12 weeks off, and then 4 consecutive weeks on. Questionnaires wererepeatedly distributed to about 800 office workers to obtain subjectiveopinions regarding environmental satisfaction and allergy symptoms(categories included systemic, mucosal, respiratory, musculo-skeletal, and“any symptomâ€) during the different time intervals.The concentration of microbes on the coils and in the drip pans wasdetermined by placing sterile 5 cm x 5 cm “coupons†of sheet metal on thesurfaces (exposed directly to the UVGI), and then placing the exposedcoupons on a Petri dish containing culture media (Sabouraud or MEA), andincubating the dishes. Coupons (receiving no UVGI) were also placed on thefilters. Air samples indoors and outdoors were obtained with Burkardvolumetric air samplers (with Petri dishes) to determine the concentrationof fungal spores. A total of 1240 samples were assayed.Endotoxin concentrations were determined using volumetric sampling andpolycarbonate filter cassettes for the air, and by washings directly fromthe dust impacted on the coupon surfaces. A total of 284 samples wereassayed. Airborne endotoxin was not detectable at workstations with the UVGIeither on or off and there was a slight increase in levels on the filtercoupons with the UVGI on. The amount of endotoxin on the coil coupon droppedfrom 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 ofculturable spores per 25 cm2 on all coupons was very low, and averaged atthe cooling coil from 0 (UVGI on) to about 4 (UVGI off) or far less than onespore per cm2 after a 4- or 12-week exposure period. The coupons on thefilters collected 3 cfu/coupon (UVGI off) and 2 cfu/coupon (UVGI on). Thecoupons may not have been very efficient collectors since they lacked a“sticky†coating and were positioned perpendicular to the air flows and thusobstructed the stream lines. In addition, the irradiated coupons wereexposed directly to the UVGI, whereas microbes on an actual HVAC surfacewould have received incident light at a variety of angles, the intensity ofwhich would be attenuated by the dust accumulations.The data and results for different seasons were not separated. Since inMontreal there is a long heating season and a short cooling season, theexpected results for each season should be quite different. In addition,during the heating season there is no condensation of moisture to promotemicrobial growth. In fact, in the presence of minimal dust on the couponsand few organisms, and without moisture, there is little opportunity for anymicrobial amplification, either in the heating or cooling season.Despite the reported reduction in symptoms indoors at work during theUVGI-on periods, no statistically significant differences were reported inthe indoor air concentrations of microbes at work stations; thus the authorswere left with no explanation for the reported reduction in symptomsassociated with UVGI. (The authors postulated that the UVGI radiation mayhave somehow reduced the aerosolization of microbial antigenic proteins.)Suggests to me that if you operate the building the way is was designed and you perform operations & maintanence (O & M) correctly that you won't have problem. Thus, UV is for poorly maintained places??

Clearly, UV is a matter of residence time of the agent in relation to the radiation source. Although minimizing the amount on the coil to minimize aerosolization makes sense, it ignores the total volume and residence time of any aerosols already airborne (that may or may not be impacted on the coils) thus it ignores probability of desctruction (dose-response thing) and dilution.

Having said that, it has been show as far back as 1935 that UV can reduce infections in high occupancy spaces (hospitals and even school rooms [Wells, Wells, and Wilder: Experimental Control of Epidemic Spread of Contagion. 1942 for 3 schools]. [incidentally UV can work on fungi in certain circumstances] The factors are plenty and some could be arranged:

Sensitivity of population (general, babies, health adults, immune or adversely affected; it has been shown that pre-Ozone exposure can increase risk of infection, as can other infectionious agents immediately prior, e.g, infuenza prior to a bacterial challenge)

Agent(s) of concern

HVAC filtration

Air Changes per Hour (ACH) nominal and source

Recirculation amount and type (open air plenum vs returns)

Local ventilation supply (dilivery and patterns of movement into breating zone)

Velocity of air delivery (settling time in ducts and residence time of airbiorne bioaerosols past UV)

Occupation density (distance of transmission person-to-person, frequency of transmission to air, bioarosol agent generation rate, generation rate of secondary carriers (skin flakes for instance))

Building materials (static pull, carpeting as a sink, water resisitance of materials to lower surface RH and lower survival rate; internally lined Fiberglass)

Building environment (RH, Temp - functional relation to bioaerosol survival rates and human susceptibility [dryness on asthma, respiratory infections, etc.]; combustion sources)

Location of UV unit, intensity of source, wavelength

To prevent microbial growth due to moisture or high relative humidity inHVAC systems, the most important components of hygiene will always be properdesign to begin with, adequate filtration (a minimum of MERV 6-8), andregular maintenance. [Excellent points] Though UVGI may certainly serve as an adjunct indisinfecting exposed air and reducing microbial growth on irradiatedsurfaces, the impact on overall indoor air quality of UVGI alone should notbe overstated.[Well put] C. MayMay Indoor Air Investigations LLC1522 Cambridge StreetCambridge, MA 02139www.mayindoorair.comwww.myhouseiskillingme.comiamnotanairhead 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,> 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]



Tony Havics,

Please help me. I'm confused why you are mentioning the TLV allowance for UV radiation.

Aren't we speaking about a UV bulb totally enclosed in an air duct?? Where does employee safety become a concern if the installation is totally enclosed and requires an electrical interlock and if the duct works are properly labeled and the maintenance personal are educated in the nature of the installation??

I am of the opinion there need be no safety hazard with proper electrical interlocks and safety labeling.

I agree your statement that "UV is a matter of residence time of the agent in relation to the radiation source" is true but only where the germicidal instrument is the UV bulb.

However where the UV bulb is used simply as an energy source to produce a fume of hydro peroxide radicals at a catalytic target there is an entirely different equation and residence time seems of no consequence.

Also let's not forget humidity is equally a prime factor in the killing success of the system where UV is used to generate advanced oxidizers.

BTW I see no TLV or BEI listed for hydro peroxide radicals or for O4, O5, or O6 in the workplace atmosphere. Might that be because there is no known hazard for these oxidizers?

Ken Gibala

RE: Re: efficacy of germicidal UV

Interesting.See comments below plus: UV exposure should be down around 1 mW/cm2 (see ACGIH TLV on UV by wavelength)

Tony......................................................................... "Tony" Havics, CHMM, CIH, PEpH2, LLCPO Box 34140Indianapolis, IN 46234 cell90% 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.-----Original Message-----From: iequality [mailto:iequality ] On Behalf Of Jeff MaySent: Friday, April 07, 2006 6:54 PMTo: iequality Subject: Re: efficacy of germicidal UV,I posted this when the study came out:In a recent paper, “Effect of ultraviolet germicidal lights in officeventilation systems on workers’ health and well-being: double-blind multiplecrossover trial,†(Lancet 2003; 362: 1785-91), the authors Menzies et.al.concluded that “installation of UVGI in most North American offices couldresolve work-related symptoms in about 4 million employees, caused bymicrobial contamination of the heating, ventilation and air-conditioningsystems.â€Despite the fact that ultraviolet germicidal irradiation (UVGI) has beenshown in many previous studies to reduce airborne contagion, I believe thatthe conclusion of this study overstates the impact of UVGI on HVAC systemsand office indoor air quality. (Agree)Three healthy, well-ventilated (peak values of carbon dioxide were under 620ppm) office buildings in Montreal, Canada were evaluated over the course ofone year (July 1999 to July 2000). In the study, UV lamps (245-266 nmwavelength band), rated at 450 mW/cm2 at a distance of one meter, weremounted with reflectors 15 to 74 cm from the cooling coils and drip pans. Atthis level of irradiation (greater than what is typical - no kidding - Hart , back in 1942 noted that a kill rate of >99% at 3 min for 30 mW/cm2 at the surface), the authorsestimated that the survival time for resistant organisms would be less than4 minutes. Within the HVAC system, the UVGI lamps were cycled, operating for12 weeks off, and then 4 consecutive weeks on. Questionnaires wererepeatedly distributed to about 800 office workers to obtain subjectiveopinions regarding environmental satisfaction and allergy symptoms(categories included systemic, mucosal, respiratory, musculo-skeletal, and“any symptomâ€) during the different time intervals.The concentration of microbes on the coils and in the drip pans wasdetermined by placing sterile 5 cm x 5 cm “coupons†of sheet metal on thesurfaces (exposed directly to the UVGI), and then placing the exposedcoupons on a Petri dish containing culture media (Sabouraud or MEA), andincubating the dishes. Coupons (receiving no UVGI) were also placed on thefilters. Air samples indoors and outdoors were obtained with Burkardvolumetric air samplers (with Petri dishes) to determine the concentrationof fungal spores. A total of 1240 samples were assayed.Endotoxin concentrations were determined using volumetric sampling andpolycarbonate filter cassettes for the air, and by washings directly fromthe dust impacted on the coupon surfaces. A total of 284 samples wereassayed. Airborne endotoxin was not detectable at workstations with the UVGIeither on or off and there was a slight increase in levels on the filtercoupons with the UVGI on. The amount of endotoxin on the coil coupon droppedfrom 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 ofculturable spores per 25 cm2 on all coupons was very low, and averaged atthe cooling coil from 0 (UVGI on) to about 4 (UVGI off) or far less than onespore per cm2 after a 4- or 12-week exposure period. The coupons on thefilters collected 3 cfu/coupon (UVGI off) and 2 cfu/coupon (UVGI on). Thecoupons may not have been very efficient collectors since they lacked a“sticky†coating and were positioned perpendicular to the air flows and thusobstructed the stream lines. In addition, the irradiated coupons wereexposed directly to the UVGI, whereas microbes on an actual HVAC surfacewould have received incident light at a variety of angles, the intensity ofwhich would be attenuated by the dust accumulations.The data and results for different seasons were not separated. Since inMontreal there is a long heating season and a short cooling season, theexpected results for each season should be quite different. In addition,during the heating season there is no condensation of moisture to promotemicrobial growth. In fact, in the presence of minimal dust on the couponsand few organisms, and without moisture, there is little opportunity for anymicrobial amplification, either in the heating or cooling season.Despite the reported reduction in symptoms indoors at work during theUVGI-on periods, no statistically significant differences were reported inthe indoor air concentrations of microbes at work stations; thus the authorswere left with no explanation for the reported reduction in symptomsassociated with UVGI. (The authors postulated that the UVGI radiation mayhave somehow reduced the aerosolization of microbial antigenic proteins.)Suggests to me that if you operate the building the way is was designed and you perform operations & maintanence (O & M) correctly that you won't have problem. Thus, UV is for poorly maintained places??

Clearly, UV is a matter of residence time of the agent in relation to the radiation source. Although minimizing the amount on the coil to minimize aerosolization makes sense, it ignores the total volume and residence time of any aerosols already airborne (that may or may not be impacted on the coils) thus it ignores probability of desctruction (dose-response thing) and dilution.

Having said that, it has been show as far back as 1935 that UV can reduce infections in high occupancy spaces (hospitals and even school rooms [Wells, Wells, and Wilder: Experimental Control of Epidemic Spread of Contagion. 1942 for 3 schools]. [incidentally UV can work on fungi in certain circumstances] The factors are plenty and some could be arranged:

Sensitivity of population (general, babies, health adults, immune or adversely affected; it has been shown that pre-Ozone exposure can increase risk of infection, as can other infectionious agents immediately prior, e.g, infuenza prior to a bacterial challenge)

Agent(s) of concern

HVAC filtration

Air Changes per Hour (ACH) nominal and source

Recirculation amount and type (open air plenum vs returns)

Local ventilation supply (dilivery and patterns of movement into breating zone)

Velocity of air delivery (settling time in ducts and residence time of airbiorne bioaerosols past UV)

Occupation density (distance of transmission person-to-person, frequency of transmission to air, bioarosol agent generation rate, generation rate of secondary carriers (skin flakes for instance))

Building materials (static pull, carpeting as a sink, water resisitance of materials to lower surface RH and lower survival rate; internally lined Fiberglass)

Building environment (RH, Temp - functional relation to bioaerosol survival rates and human susceptibility [dryness on asthma, respiratory infections, etc.]; combustion sources)

Location of UV unit, intensity of source, wavelength

To prevent microbial growth due to moisture or high relative humidity inHVAC systems, the most important components of hygiene will always be properdesign to begin with, adequate filtration (a minimum of MERV 6-8), andregular maintenance. [Excellent points] Though UVGI may certainly serve as an adjunct indisinfecting exposed air and reducing microbial growth on irradiatedsurfaces, the impact on overall indoor air quality of UVGI alone should notbe overstated.[Well put] C. MayMay Indoor Air Investigations LLC1522 Cambridge StreetCambridge, MA 02139www.mayindoorair.comwww.myhouseiskillingme.comiamnotanairhead 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,> 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]

I recognize that most are used in/near blower or coil or just up or downstream. I now that the general person

Maintenance issue as a reminder. I've seena lot of HVAC techs who don't know there is a hazard there - and sales reps who don't communicate it (unfortunate for the good ones).

Tony

........................................................................... "Tony" Havics, CHMM, CIH, PEpH2, LLCPO Box 34140Indianapolis, IN 46234 cell90% 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.

-----Original Message-----From: iequality [mailto:iequality ] On Behalf Of kengib .Sent: Saturday, April 08, 2006 9:38 PMTo: iequality Subject: Re: Re: efficacy of germicidal UV

Tony Havics,

Please help me. I'm confused why you are mentioning the TLV allowance for UV radiation.

Aren't we speaking about a UV bulb totally enclosed in an air duct?? Where does employee safety become a concern if the installation is totally enclosed and requires an electrical interlock and if the duct works are properly labeled and the maintenance personal are educated in the nature of the installation??

I am of the opinion there need be no safety hazard with proper electrical interlocks and safety labeling.

I agree your statement that "UV is a matter of residence time of the agent in relation to the radiation source" is true but only where the germicidal instrument is the UV bulb.

However where the UV bulb is used simply as an energy source to produce a fume of hydro peroxide radicals at a catalytic target there is an entirely different equation and residence time seems of no consequence.

Also let's not forget humidity is equally a prime factor in the killing success of the system where UV is used to generate advanced oxidizers.

BTW I see no TLV or BEI listed for hydro peroxide radicals or for O4, O5, or O6 in the workplace atmosphere. Might that be because there is no known hazard for these oxidizers?

Ken Gibala

RE: Re: efficacy of germicidal UV

Interesting.See comments below plus: UV exposure should be down around 1 mW/cm2 (see ACGIH TLV on UV by wavelength)

Tony......................................................................... "Tony" Havics, CHMM, CIH, PEpH2, LLCPO Box 34140Indianapolis, IN 46234 cell90% 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.-----Original Message-----From: iequality [mailto:iequality ] On Behalf Of Jeff MaySent: Friday, April 07, 2006 6:54 PMTo: iequality Subject: Re: efficacy of germicidal UV,I posted this when the study came out:In a recent paper, “Effect of ultraviolet germicidal lights in officeventilation systems on workers’ health and well-being: double-blind multiplecrossover trial,†(Lancet 2003; 362: 1785-91), the authors Menzies et.al.concluded that “installation of UVGI in most North American offices couldresolve work-related symptoms in about 4 million employees, caused bymicrobial contamination of the heating, ventilation and air-conditioningsystems.â€Despite the fact that ultraviolet germicidal irradiation (UVGI) has beenshown in many previous studies to reduce airborne contagion, I believe thatthe conclusion of this study overstates the impact of UVGI on HVAC systemsand office indoor air quality. (Agree)Three healthy, well-ventilated (peak values of carbon dioxide were under 620ppm) office buildings in Montreal, Canada were evaluated over the course ofone year (July 1999 to July 2000). In the study, UV lamps (245-266 nmwavelength band), rated at 450 mW/cm2 at a distance of one meter, weremounted with reflectors 15 to 74 cm from the cooling coils and drip pans. Atthis level of irradiation (greater than what is typical - no kidding - Hart , back in 1942 noted that a kill rate of >99% at 3 min for 30 mW/cm2 at the surface), the authorsestimated that the survival time for resistant organisms would be less than4 minutes. Within the HVAC system, the UVGI lamps were cycled, operating for12 weeks off, and then 4 consecutive weeks on. Questionnaires wererepeatedly distributed to about 800 office workers to obtain subjectiveopinions regarding environmental satisfaction and allergy symptoms(categories included systemic, mucosal, respiratory, musculo-skeletal, and“any symptomâ€) during the different time intervals.The concentration of microbes on the coils and in the drip pans wasdetermined by placing sterile 5 cm x 5 cm “coupons†of sheet metal on thesurfaces (exposed directly to the UVGI), and then placing the exposedcoupons on a Petri dish containing culture media (Sabouraud or MEA), andincubating the dishes. Coupons (receiving no UVGI) were also placed on thefilters. Air samples indoors and outdoors were obtained with Burkardvolumetric air samplers (with Petri dishes) to determine the concentrationof fungal spores. A total of 1240 samples were assayed.Endotoxin concentrations were determined using volumetric sampling andpolycarbonate filter cassettes for the air, and by washings directly fromthe dust impacted on the coupon surfaces. A total of 284 samples wereassayed. Airborne endotoxin was not detectable at workstations with the UVGIeither on or off and there was a slight increase in levels on the filtercoupons with the UVGI on. The amount of endotoxin on the coil coupon droppedfrom 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 ofculturable spores per 25 cm2 on all coupons was very low, and averaged atthe cooling coil from 0 (UVGI on) to about 4 (UVGI off) or far less than onespore per cm2 after a 4- or 12-week exposure period. The coupons on thefilters collected 3 cfu/coupon (UVGI off) and 2 cfu/coupon (UVGI on). Thecoupons may not have been very efficient collectors since they lacked a“sticky†coating and were positioned perpendicular to the air flows and thusobstructed the stream lines. In addition, the irradiated coupons wereexposed directly to the UVGI, whereas microbes on an actual HVAC surfacewould have received incident light at a variety of angles, the intensity ofwhich would be attenuated by the dust accumulations.The data and results for different seasons were not separated. Since inMontreal there is a long heating season and a short cooling season, theexpected results for each season should be quite different. In addition,during the heating season there is no condensation of moisture to promotemicrobial growth. In fact, in the presence of minimal dust on the couponsand few organisms, and without moisture, there is little opportunity for anymicrobial amplification, either in the heating or cooling season.Despite the reported reduction in symptoms indoors at work during theUVGI-on periods, no statistically significant differences were reported inthe indoor air concentrations of microbes at work stations; thus the authorswere left with no explanation for the reported reduction in symptomsassociated with UVGI. (The authors postulated that the UVGI radiation mayhave somehow reduced the aerosolization of microbial antigenic proteins.)Suggests to me that if you operate the building the way is was designed and you perform operations & maintanence (O & M) correctly that you won't have problem. Thus, UV is for poorly maintained places??

Clearly, UV is a matter of residence time of the agent in relation to the radiation source. Although minimizing the amount on the coil to minimize aerosolization makes sense, it ignores the total volume and residence time of any aerosols already airborne (that may or may not be impacted on the coils) thus it ignores probability of desctruction (dose-response thing) and dilution.

Having said that, it has been show as far back as 1935 that UV can reduce infections in high occupancy spaces (hospitals and even school rooms [Wells, Wells, and Wilder: Experimental Control of Epidemic Spread of Contagion. 1942 for 3 schools]. [incidentally UV can work on fungi in certain circumstances] The factors are plenty and some could be arranged:

Sensitivity of population (general, babies, health adults, immune or adversely affected; it has been shown that pre-Ozone exposure can increase risk of infection, as can other infectionious agents immediately prior, e.g, infuenza prior to a bacterial challenge)

Agent(s) of concern

HVAC filtration

Air Changes per Hour (ACH) nominal and source

Recirculation amount and type (open air plenum vs returns)

Local ventilation supply (dilivery and patterns of movement into breating zone)

Velocity of air delivery (settling time in ducts and residence time of airbiorne bioaerosols past UV)

Occupation density (distance of transmission person-to-person, frequency of transmission to air, bioarosol agent generation rate, generation rate of secondary carriers (skin flakes for instance))

Building materials (static pull, carpeting as a sink, water resisitance of materials to lower surface RH and lower survival rate; internally lined Fiberglass)

Building environment (RH, Temp - functional relation to bioaerosol survival rates and human susceptibility [dryness on asthma, respiratory infections, etc.]; combustion sources)

Location of UV unit, intensity of source, wavelength

To prevent microbial growth due to moisture or high relative humidity inHVAC systems, the most important components of hygiene will always be properdesign to begin with, adequate filtration (a minimum of MERV 6-8), andregular maintenance. [Excellent points] Though UVGI may certainly serve as an adjunct indisinfecting exposed air and reducing microbial growth on irradiatedsurfaces, the impact on overall indoor air quality of UVGI alone should notbe overstated.[Well put] C. MayMay Indoor Air Investigations LLC1522 Cambridge StreetCambridge, MA 02139www.mayindoorair.comwww.myhouseiskillingme.comiamnotanairhead 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,> 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]

Jeff

I am with you 100%, and for other reasons as well.

I have never yet seen an installation where there were not UV light leaks from the leaky ducts that these bulbs saw as home.

I have never yet seen proper interconnects.

I have often smelled something suspiciously like ozone in these crappy installations (fan not running, but no interconnect).

The occupants were sometimes feeling worse after the UV was installed, possibly because they were even less careful about keeping the place and the filters clean (none of the installation bathed the filters properly).

When installed properly this UV technology may work, maybe only until it needs some maintenance, but it sure isn't working now.

Jim H. White SSC

Date: Sun, 09 Apr 2006 14:12:09 -0400 Subject: Re: efficacy of germicidal UVMike, 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. MayMay Indoor Air Investigations LLC1522 Cambridge StreetCambridge, MA 02139www.mayindoorair.comwww.myhouseiskillingme.com

[Guest guest]

Just a note of caution from experience - U.V. lamps installed in such a manner

as to expose media filters to the light will cause a rapid disintegration of the

filter material.

Curtis Redington, RS

Environmental Quality Specialist

City of Wichita Dept. of Environmental Health

Wichita, KS

Re: efficacy of germicidal UV

,

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,

>

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[Guest guest]

Geyer Wrote:

" OSHA requires that all commercial HVAC systems to be inspected and

serviced at least annually, and changing filters does not constitute:

" inspection and service. "

I am not familiar with this requirement. Is there a citation handy?

Thanks.

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[Guest guest]

Good points Wane.

Ken - (aka kengib) I have a couple of questions for you. Please answer them

honestly.

Do you sell FreshAirLiving air cleaners? Also, are you, or do you claim to

be a Certified Mold Inspector, and if so, certified through whom?

Thank you.

Stacey Champion

Re: efficacy of germicidal UV

" O5 " ? what the heck is " O5 " ? how exactly does a molecule like that

form? what holds it together, even for a mini-micro-femtosecond?

how is it even possible? some pretty amazing electron sharing is

going on here. (maybe it was left behind when those UFOs landed.)

" advanced oxygen compounds " ? surely, this is a term created by a

marketing group.

O5.... hmmm, like in " Hawaii-O-5 " ? no wait a minute, that was 5-O.

(book 'em, Dan-o.)

for a good read on the FACTS about ozone, one of the best papers in

the literature remains: CJ Weschler (2000) " Ozone in Indoor

Environments: Concentration and Chemistry " , Indoor Air, 10:269-288.

from p. 270: " Ozone is a relatively stable molecule; only at high

ozone concentrations and/or elevated temperatures does it decompose

to oxygen at a significant rate. " and " Ozone is a very strong

oxidizing agent. Just a few species, such as fluorine, the

perxenate ion, atomic oxygen and the hydroxyl radical are more

powerful oxidants. However, this fact should not be misconstrued.

Although ozone is capable of oxidizing numerous gas phase species, a

large fraction of these ractions occur at a slow rate... "

read all about it.

Wane

<><><><><><><><><><><>

Wane A. Baker, P.E., CIH

Director, Air Quality Services

MICHAELS ENGINEERING INC.

" Real Professionals. Real Solutions "

811 Monitor Street, Suite 100

PO Box 2377

La Crosse, Wisconsin 54602

Phone , ext. 484

Cell

Fax

mailto:wab@...

On the web at: http://www.michaelsengineering.com

" To love what you do and feel that it matters - how could anything

be more fun? " - Graham

>

> With the UVGI installations recently discussed here where a UV

bulb is installed before the air handler it is doubtful any ozone

could survive the turbulence of the fans. We should understand the

physical and chemical nature of ozone. Let's review: Ozone is

extremely fragile or unstable. It has a normal half life of less

than 25 minutes. Thus overnight there should be virtually no

natural ozone remaining in a residence unless windows are allowed to

be open for ventilation. Any turbulence will reduce the half life to

minutes.

>

> With UV bulbs there can be ozone produced at the wave length of

UVA. I'm told there is little or no ozone produced at the

wavelength of UVC; in fact, the recent Lancet article referenced by

Jeff Mays showed that with the UV cycled on there was less

measurable ozone in the room than when off indicating that UVC

consumes [breaks down] ozone.

>

> To go one step further.......The principle of photohydroionization

is to use a broad band bulb operating the range between 185 nm and

254 um and focused toward a target with an appropriate catalytic

coating. At 185 nm ozone is produced and simultaneously consumed by

uv at 254 nm. In the process with the rh above 10%, quantities of

advanced oxygen compounds hydro peroxide and hydroxyl radicals are

produced along with amounts of O5. These substances rapidly destroy

the cell membranes of most microbials without presenting any known

hazard to humans.

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[Guest guest]

Ron,

I have ozone sensitivity, mainly from working with and selling ozone

generators. I can assure you that any ozone in the system WILL make it

throughout the home and persist for a time. Ozone will generally last 25

-30 minutes, sometimes longer. Ozone has no business being generated in an

occupied building. I do not know (yet) about the half life of super oxide

ions. I am told that they will also persist, but I read articles that say

that they will not survive. The hydroxyl radicals probably will not get

out.

I feel that the real lie in the statement is " deliver safe oxidizers " .

Oxidizers are active free radicals that will destroy organics, of which WE

are one. We try to have a diet that includes antioxidants to our body to

combat free radicals, yet we spend good money to generate free radicals

inside our occupied spaces. Good filtration, proper air changes and good

maintenance are what we should be doing, not introducing additional

chemistry that has unknown long term effects.

These statements have the sound of marketing hype to me.

Bruce

Re: efficacy of germicidal UV

Bruce and Jeff,

If I understand correctly, you and Jeff (#6613) maintain that

of the " super oxidizers " produced by the photocatalytic process, only

the ozone (if any is produced by the UV lamps used as the energy

source for the photocatalyst) lasts long enough to leave the air

handler. Thus the statement " In just a few minutes you can install

state-of-the-art air purification technology into your HVAC

system . . . " which " . . . utilizes your HVAC fan to deliver safe

oxidizers and super-oxide ions throughout your home, . . . " has no

scientific basis for its claim.

Ron

> > >

> > >>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.

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of your

> own that go beyond 'fair use', you must obtain permission from the

copyright

> owner.

>