TB Infection Control

Dear Susan,
 
I don't think that higher fan speed reduces upper room UVGI fixture effectiveness.  Actually more air mixing is better, the limiting factor for too quick fan rotation may be occupants comfort, not air decontamination efficiency. Theoretically ceiling  fans should be more efficient in this regard than wall mounted or floor fans, because they provide more vertical air mixing than horizontal. In our study the floor standing fan improved upper room UVGI air decontamination efficiency for 16% (we have not tested ceiling fan).
 Hard to say "how slow is slow". I think very low vertical air velocity of 0,25 m/s, which is considered only slightly sensible, still provides sufficient air mixing in the room. Ceiling fans usually provide much higher velocities (which is good for upper room UVGI). In low humidity settings (like Central Asia) at T 26C occupants prefer for comfort 0,4 m/s, at T 32C -  1,8 m/s.
 
Administratively and practically ceiling fans are easier to use in high risk settings (not in laboratory procedures rooms, since they can disrupt local ventilation and BSC function). 
 
Needless to say how important to educate staff and patients that these fans reduce TB transmission ...

Dear Susan,
 
I don't think that higher fan speed reduces upper room UVGI fixture effectiveness.  Actually more air mixing is better, the limiting factor for too quick fan rotation may be occupants comfort, not air decontamination efficiency. Theoretically ceiling  fans should be more efficient in this regard than wall mounted or floor fans, because they provide more vertical air mixing than horizontal. In our study the floor standing fan improved upper room UVGI air decontamination efficiency for 16% (we have not tested ceiling fan).
 Hard to say "how slow is slow". I think very low vertical air velocity of 0,25 m/s, which is considered only slightly sensible, still provides sufficient air mixing in the room. Ceiling fans usually provide much higher velocities (which is good for upper room UVGI). In low humidity settings (like Central Asia) at T 26C occupants prefer for comfort 0,4 m/s, at T 32C -  1,8 m/s.
 
Administratively and practically ceiling fans are easier to use in high risk settings (not in laboratory procedures rooms, since they can disrupt local ventilation and BSC function). 
 
Needless to say how important to educate staff and patients that these fans reduce TB transmission risk only if used with properly installed, maintained and used upper room UVGI.
 
So - I would recommend to install ceiling fans available in local market and include upper room UVGI effectiveness ussues into TB IC education program.
 
Hope it helps,

Grigory

--------- 
Dr. Grigory V. Volchenkov

Head Doctor
Vladimir Oblast TB Dispansery

Sudogodskoe shosse, 63
Vladimir 600023 RUSSIA

phone/fax work: +7(4922)323265
mobile +7 9206253227; +7 9190189226

Dear All
I not sure I totally agree with a fan to improve UVGI. There is centrifugal force of air movement which is not well controlled and the dispersal rates increase dramatically. Trying to get a fan and a UVGI should be in well controlled circumstances rather than an open room where air can escape. I think we need to be reminded that air has to move across the UVGI at a particular rate and that the mixing is to ensure that all the air circulates past the light. I am not sure that a ceiling fan can manage that.
I would love to hear from others
Regards
Shaheen

Prof Shaheen Mehtar
MBBS, FRC Path (UK), FCPath (Micro) (SA), MD (Lon)
Chair of Infection Prevention and Control Africa Network (IPCAN)
Head of Academic Unit for Infection Prevention and Control
Tygerberg Hospital &Fac of Health Sciences,  Stellenbosch Uni
PO Box 19063,
Tygerberg 7505, Cape Town
Tel: +27 21 938 5051
Fax: + 27 21 938 5065
Mobile: +27 82 852 3697
http://www.sun.ac.za/uipc
Register now for the 3rd IPCAN conference Namibia
1-3rd November, 2011
http://www.ipcan.co.za

A little more info is required here first. What is the size of the room? What type of uvgi device are you using and what is their output? How many? placed where?
regards.
Paul.

I agree entirely with Grigory. There are study after study in experimental chambers showing that paddle fans always increase the effectiveness of upper room UVGI compared to natural vertical air mixing. One study by Riley and Permutt from 1972 did show that temperature generated air mixing, that is, delivering warm air low in the room which then rises, was even more effective than fans, but that requires a ventilation system and depends on the season (ie, delivering cool air to the upper room in summer to allow mixing), so is not practical. In Shelly Miller's more recent room studies using mixing fans (she used floor fans) were also effective, but were high velocity and therefor noisy and drafty. Our own studies in South Africa showing 80% efficacy used commercial ceiling fans run at slow speed. The speed considerations that Grigory explained are exactly correct - comfort being the main criteria. For reversible fans, most occupants prefer a downdraft during hot weather and an a less perceptible updraft during warm weather. Generally, the more mixing the better, within what is comfortable for occupants. Obviously, most ceiling fans are specifically designed for occupant comfort so this should not be a problem. We ...

I agree entirely with Grigory. There are study after study in experimental chambers showing that paddle fans always increase the effectiveness of upper room UVGI compared to natural vertical air mixing. One study by Riley and Permutt from 1972 did show that temperature generated air mixing, that is, delivering warm air low in the room which then rises, was even more effective than fans, but that requires a ventilation system and depends on the season (ie, delivering cool air to the upper room in summer to allow mixing), so is not practical. In Shelly Miller's more recent room studies using mixing fans (she used floor fans) were also effective, but were high velocity and therefor noisy and drafty. Our own studies in South Africa showing 80% efficacy used commercial ceiling fans run at slow speed. The speed considerations that Grigory explained are exactly correct - comfort being the main criteria. For reversible fans, most occupants prefer a downdraft during hot weather and an a less perceptible updraft during warm weather. Generally, the more mixing the better, within what is comfortable for occupants. Obviously, most ceiling fans are specifically designed for occupant comfort so this should not be a problem. We are currently doing computer flow dynamics (CFD) studies of ceiling fans in conjunction with UVGI. It has been difficult to model, but very preliminary results under the circumstances modeled do suggest that very high speeds could generate some air pockets (eddies) in the lower room that do not mix well, but those higher speeds are not likely to be well tolerated by occupants either. Regarding exposure of organisms, slow air movement allows more UV exposure per pass, while faster air movement allows more passes through the UV irradiated zone. In theory, it comes out the same, but for risk of infection, disinfection with fewer passes up and down are desirable.

This is not rocket science. The goal is simply to achieve reliable air mixing between the upper and lower room by a method that is quiet, inexpensive, and does not make the room uncomfortable. There is no need to worry about an exact RPM rate. Ceiling fans are designed to do this job and have proven over decades to be highly effective. This has been proven experimentally. There are many other, more complicated application issues around UVGI that are less clear, like room dosing (how much UVGI to use), but the air mixing issue is an easy one: simply provide enough mixing to move air and maintain occupant comfort.

One last point of clarification that Grigory made: without UVGI in the upper room ceiling fans generally DO NOT increase the numbers of air changes between the room and the outdoors and therefore are not a means of air disinfection. By mixing room air they may decrease risk locally, but only by spreading that risk through a larger volume of room air. An upper air UVGI-air mixing system does not provide real air changes, of course, but "equivalent" air changes from an air disinfection perspective.

Thanks for the comments. I was concerned that a commercial fan, even at a slow speed, would be moving air through the irradiance zone too quickly to be effectively bactericidal. We are implementing this in 3 large inpatient facilities and approx 50 ambulatory treatment points, and xray rooms. It's quite a large financial commitment but our options for IC during a severe winters is limited. Thanks again for the advice.

Susan Adolph
ICO Uzbekistan/Tajikistan
MSF

To reiterate, more rapid vertical air mixing does not much affect efficacy because at faster rates droplet nuclei return to the upper room more often and exposure time is similar.

We could take this off line, but I would like to ask you publicly for the benefit of others what brand, style, and wattage UV fixtures you are using, and if you have a qualified consultant to: 1) plan the installation?, 2) commission it (meter for safety and efficacy) before you turn it on?, and 3) have a plan for long term maintenance including cleaning and re-lamping? Grigory Volchenkov has found that you can save a lot of money by not re-lamping on a annual basis, but metering each lamp in a standardized way and replacing those lamps which fall below, I believe, 60% of expected output. Like fluorescent lamps, UV lamps have mercury in them and should not end up in a landfill. You need a plan for safe disposal of all fluorescent lamps, including used UV lamps.



Ed

Dear All,
Does anyone the author of the TB infection baseline tool found on ghdoline? www.ghdonline tbic-baseline-assessment tool version 10 April 8. If you know it kindly send me the name, as I need it for referencing purposes.
Esther Buregyeya

Hi Susan,with respect to all, the higher the fan speed, the less likely the efficacy of any upper air device (above a certain baseline). Work out the distance between the placement of the devices, then determine the average irradiance of said emitters/ devices in that area, you should be able to get the figure from the suppliers polar graphs, determine from that the amount of time the bugs need to be in that space " kill zone" , and then you can tell if your design is effective by using an anenometer measuring the air flow in the intended kill zones. If the irradiance is too weak, and / or fan speed to high, you run the risk of re activation if bugs are not killed properly on first pass. This is one of the problems with upper air device installations. Regards, Paul. You can e mal me at if you like.

Bonjour,
 
Dans notre LNRM, on utilise pas Les ventilateurs de plafond mais plutôt le travail à travers des ESB.
 
Salutations.

------------------------------------------------------
Dr Mohamed Brahim Elkory
Directeur INRSP
Responsable du LNRM
BP : 695
Tél.:+222 45 25 31 34
Fax: +222 45 29 26 45
e-mail:
Nouakchott - Mauritanie

Hi Ed,

I am happy to answer your questions publicly, please bear in mind they do not necessarily reflect the opinions of my organization. Do we have a qualified consultant? This is a resource limited setting in which has no experience with upper room UVGI. So there are no consultants from within the country. Personally, most of what I know about UV was taught to me by you and Grigory at the last Harvard course and I also have the support of a biomedical engineer via phone and internet. Our fixtures are a copy of a design of a well known commercial company who was willing to let us copy them. With these designs we are working together with a local manufacturer to produce them in quantity. This is a solution to importation problems, and also provides some sustainable access to these fixtures for a future when our organization is no longer here supporting the local MoH. They use a 30w lamp (imported Philips TUV-30). As for maintenance, this is a complicated issue. It will not be possible to measure all these lamps on a regular basis due their wide spread geographical distribution and limited transportation capacity and manpower on ...

Hi Ed,

I am happy to answer your questions publicly, please bear in mind they do not necessarily reflect the opinions of my organization. Do we have a qualified consultant? This is a resource limited setting in which has no experience with upper room UVGI. So there are no consultants from within the country. Personally, most of what I know about UV was taught to me by you and Grigory at the last Harvard course and I also have the support of a biomedical engineer via phone and internet. Our fixtures are a copy of a design of a well known commercial company who was willing to let us copy them. With these designs we are working together with a local manufacturer to produce them in quantity. This is a solution to importation problems, and also provides some sustainable access to these fixtures for a future when our organization is no longer here supporting the local MoH. They use a 30w lamp (imported Philips TUV-30). As for maintenance, this is a complicated issue. It will not be possible to measure all these lamps on a regular basis due their wide spread geographical distribution and limited transportation capacity and manpower on the part of local counterparts. We do have 2 UVC meters and therefore will likely implement a hybrid plan of measuring output in our inpatient facilities but changing the lamps on a schedule in the outpatient locations. The outpatient maintenance plan is plagued with problems however due to intermittent electricity supply (sometimes as little 3 hours a day), cold indoor temperatures and a lack of even basic cleaning supplies. Nonetheless, it remains an important intervention due to the lack of natural ventilation in winter. There are many more details to they plans, but I hope this gives you the basic idea.

Susan Adolph, RN
ICO Uzbekistan/Tajikistan
MSF

Hi Esther,

The tool was developed by ICAP (International Centre for AIDS Care and Treatment Programs), South Africa in 2008.

Regards,
Sabine

With all due respect, Paul, you are wrong as explained previously and as shown in many room experiments. Please provide any evidence that a higher mixing rate will reduce killing. I can and will provide many papers that prove just the opposite. It is quite different in a duct where there is flow-through and only one chance to kill the bug. There you do have to use the Westinghouse tables that tell you how much irradiance you need for a given flow rate, but for upper room UVGI, that is not the case, either in theory, or by experiment. The faster the mixing the more opportunities the bugs have to reach the upper irradiated zone. I will send the citations along from my office computer.

Ed

Just a practical tip from my side, there are single or two directional ceiling fans, they either create and down ward or can create an upward and downward flow of air. This will probably not affect the mixing of the air, but will have a great impact on patients. In winter a downward flow over the bed might feel very uncomfortable, especially when facility is not heated properly. In summer a downward flow over the bed might be a good thing. If possible get the two directional ceiling fans, and switch directions twice a year.
Regarding the "home" made lamps. I only can say have them tested. The use of cheaper materials to fabricate the lamps might be of a disadvantage later, bent reflectors, low(er) efficiency or difficult to maintain.
One other point I want to make. Is there money available to run the equipment? From my own experience I have often heard that UVGI/ventilation is not switched on because there is no money for electricity. In some cases this might be true, in others not, but it might happen that expensive installation are not used for this reason. \

Hans Mulder

Sorry, but I do agree with Paul, hence my first response but I bow to those with much greater knowledge than mine.
S

Prof Shaheen Mehtar
MBBS, FRC Path (UK), FCPath (Micro) (SA), MD (Lon)
Head of Academic Unit for Infection Prevention and Control
Tygerberg Hospital &Fac of Health Sciences, Stellenbosch Uni
PO Box 19063,
Tygerberg 7505, Cape Town
Tel: +27 21 938 5051
Fax: + 27 21 938 5065
Mobile: +27 82 852 3697
http://www.sun.ac.za/uipc
Visit the IPCAN website on
http://www.ipcan.co.za

Dear All,

Just a quick translation: Answering to Ed Nardell's question (For the benefit of others what brand, style, and wattage UV fixtures you are using, and if you have a qualified consultant to: 1) plan the installation?, 2) commission it (meter for safety and efficacy) before you turn it on?, and 3) have a plan for long term maintenance including cleaning and re-lamping?), Dr Mohamed Brahim Elkory at the National Lab in Mauritania wrote earlier that they do not use the ceiling fans and instead do the lab work in a bio safety cabinet.

For clarity, in response to Mohamed, this discussion was not about lab use of upper room UV or paddle fans in the lab setting. Usually, fans are not used in labs where concentrated cultures are being opened for fear of dissemination or contamination, and also because they may well interfere with the proper function of a biological safety cabinet. The use of upper room UV and fans is generally in clinical and other congregate settings.

Ed

I just added a document to GHDonline labelled as Riley 1971. It is two papers from the Archives of Environmental Health Here is my summary:


Download: Riley_1971_-_Arch_Environ_Health_22-1.pdf<http://www.ghdonline.org/uploads/Riley_1971_-_Arch_Environ_Health_22-1.pdf> (1.4 MB)

Summary: These two articles from the older literature show in great detail, based on room experiments, that air mixing greatly enhances the efficacy of upper room UVGI. In the first article the authors show that convection currents caused by temperature differences in the room were the most effective way to mix air - when this could be accomplished by mechanical ventilation. This is not feasible in most places in poor settings where UV is used. For most applications, ceiling fans are better. The second paper shows that air mixing doubled the effect of UVGI. Although more rapid air movement through the upper room means less exposure time per pass, it also means more passes through the upper room. There are several more papers in the literature confirming that there is no "down side" to improved air mixing when using upper room UVGI and probably no optimal fan speed, except for comfort of occupants.

To access the articles please log into GHDonline TB IC ...

Again, thank you all for your comments, they've been very helpful.

Susan Adolph

Bonjour,
 
Je vous remercie pour l'info.

Good Day

My name is Rob.
I have had nothing to add to other conversations, but this one I can
contribute to.
Ceiling Fans come in various shapes and sizes. Some with fancy lights and
two fan settings.
Industrial type with three settings - fast, medium and slow
The above are not suitable for UVGI work.
The heavy duty industrial type have five settings. These are suitable.
My experience of pedal fans, I use them where possible but you must be aware
of some of the down sides.
If the pedal fan is placed too close to the UVGI unit, in my opinion and my
tests, the unit efficiency will be reduced.
On the other hand, if the unit is placed far from the UVGI unit, the
efficiency is increased, reducing the number of pathogens in the air.
Further downsides - this is from the African scenario
Tin roof with extremely thin ceiling board: Temperatures between 25 and 30
degrees C.
Placing a pedal fan in this situation creates extreme discomfort to the
patients, as this makes the air extremely warm.
In winter or early morning when its +5 degrees C the use of a pedal fan
makes it extremely cold and ...

Good Day

My name is Rob.
I have had nothing to add to other conversations, but this one I can
contribute to.
Ceiling Fans come in various shapes and sizes. Some with fancy lights and
two fan settings.
Industrial type with three settings - fast, medium and slow
The above are not suitable for UVGI work.
The heavy duty industrial type have five settings. These are suitable.
My experience of pedal fans, I use them where possible but you must be aware
of some of the down sides.
If the pedal fan is placed too close to the UVGI unit, in my opinion and my
tests, the unit efficiency will be reduced.
On the other hand, if the unit is placed far from the UVGI unit, the
efficiency is increased, reducing the number of pathogens in the air.
Further downsides - this is from the African scenario
Tin roof with extremely thin ceiling board: Temperatures between 25 and 30
degrees C.
Placing a pedal fan in this situation creates extreme discomfort to the
patients, as this makes the air extremely warm.
In winter or early morning when its +5 degrees C the use of a pedal fan
makes it extremely cold and the patient seeks to turn the fan off.
Simple solution to the problem is : Cut a hole in the ceiling approximately
300mm diameter and fit a fan in the ceiling dragging the air out of the
building into the ceiling space.
Even if the fan is not working, it helps with the ventilation as it acts
like an additional window with fewer down sides such as gusts of wind
blowing papers around.
Further to this, putting air bricks into a building, particularly that of
doctors rooms, helps with ventilation.
In addition to this, taking a slice off the bottom of all the doors aids
with air movement. By careful design, it is possible to have a negative
pressure in the centre pulling air in from all sides.
This I have done many times and it has proved to be extremely successful and
cost effective.

Hope this information is of use to you
Rob

Dear Rob,

Thanks for your contribution, but you are mixing apples and oranges.

Let's first talk about UV air mixing systems, and then ventilation. You are mixing them up.

First, how do you know that putting a ceiling paddle fan close to a UVGI fixture decreases efficiency? How do you know that putting it further away increases efficiency? These "opinions" need to be backed up with evidence to be useful and that kind of evidence is very hard to generate. Until recently there have only been experimental room studies with aerosolized bacteria and microbiological air sampling. I have just posted two such studies. Now there are to real hospital studies using guinea pig air sampling. That by Escombe has been published and the pdf is on GHDonline. Our similar study is being prepared for publication. The sum total of the experimental data does not support what you say. Air mixing is important for upper room UVGI efficacy no matter how you do it. Occupant comfort in achieving air mixing is important, otherwise fans will be turned off. Hence, slow moving paddle fans - in one direction or the other depending on the season and temperature considerations - is the mixing method ...

Dear Rob,

Thanks for your contribution, but you are mixing apples and oranges.

Let's first talk about UV air mixing systems, and then ventilation. You are mixing them up.

First, how do you know that putting a ceiling paddle fan close to a UVGI fixture decreases efficiency? How do you know that putting it further away increases efficiency? These "opinions" need to be backed up with evidence to be useful and that kind of evidence is very hard to generate. Until recently there have only been experimental room studies with aerosolized bacteria and microbiological air sampling. I have just posted two such studies. Now there are to real hospital studies using guinea pig air sampling. That by Escombe has been published and the pdf is on GHDonline. Our similar study is being prepared for publication. The sum total of the experimental data does not support what you say. Air mixing is important for upper room UVGI efficacy no matter how you do it. Occupant comfort in achieving air mixing is important, otherwise fans will be turned off. Hence, slow moving paddle fans - in one direction or the other depending on the season and temperature considerations - is the mixing method of choice. Generally speaking, for developing country use, we are not taking about fancy fans with lights, etc, but simple, inexpensive paddle fans that have been used effectively for decades because they move air quietly and comfortably. The speed is not critical for UV efficacy as previously noted (based on experiments that I have just posted on GHDonline, and others).

Exhaust fan ventilation through the ceiling is an entirely different matter - not intending to achieve recirculation of air between the upper, irradiated zone, and the lower room. It is confusing to mix these two goals. Exhaust ventilation may be useful and appropriate in some settings, whether by whirly birds or fans, but that is not the subject of this discussion. In Russia or even in mountainous Lesotho in the cold season, exhaust ventilation is not a reasonable option. UVGI can be used when outside ventilation, natural or mechanical, cannot be relied on.

Ed

I am replying at a late stage due to some serious Lion photography in an area where the worst polluted air smell was that of fresh Elephant dung and of course no TB infected Buffalo.

The basic operation principal of Upper volume UVGI is to use a low UV-C irradiation level to irradiate a large volume of slow moving air.

UVGI must "touch" the surface area of the TB bacteria for a certain time to deactivate it. The UVGI irradiation dose is expressed as µW/cm². In older literature the Pennsylvania State University found that a dose of 10µW/cm² is effective for the deactivation of TB bacteria. When airflow or air movement is involved, the deactivation unit generally accepted and used in air conditioning systems is 10 000µWseconds/cm².

A very important factor to remember is that in a closed volume with high air movement, the TB bacteria will be "weakened" every time it passes through the irradiated area until it is deactivated. I prefer to use the term air movement because the air in the room is moved and not changed.

The important part of any UVGI design is that the irradiation dose must not be lower than ...

I am replying at a late stage due to some serious Lion photography in an area where the worst polluted air smell was that of fresh Elephant dung and of course no TB infected Buffalo.

The basic operation principal of Upper volume UVGI is to use a low UV-C irradiation level to irradiate a large volume of slow moving air.

UVGI must "touch" the surface area of the TB bacteria for a certain time to deactivate it. The UVGI irradiation dose is expressed as µW/cm². In older literature the Pennsylvania State University found that a dose of 10µW/cm² is effective for the deactivation of TB bacteria. When airflow or air movement is involved, the deactivation unit generally accepted and used in air conditioning systems is 10 000µWseconds/cm².

A very important factor to remember is that in a closed volume with high air movement, the TB bacteria will be "weakened" every time it passes through the irradiated area until it is deactivated. I prefer to use the term air movement because the air in the room is moved and not changed.

The important part of any UVGI design is that the irradiation dose must not be lower than 10µW/cm² in the area where the irradiated zones overlap. This will cause an "over designed" irradiation level near the UVGI units. Therefore only quality designed UVGI units must be used to control the over dose.

Commercial type ceiling fans must be selected by means of their performance curves. Domestic decorative types must never be used. They are manufactured for aesthetic purposes and have a poor air ovement
performance.

The mounting height of a ceiling fan plays a very important part in its performance. If a ceiling fan with the standard pendant length of 610 mm is mounted against a ceiling with a height of 2.7m, the fan will be 2.09m above the floor level. The performance curve of the ceiling fans I specify, indicate that they will be effective for a floor area of 27m² at this mounting height.

This fan delivers 14112m³/h at 290rpm. This will provide an air movement of 14112m³h / 26m² x 2.7m = 201 times below the fan. The fan rpm must therefore be reduced to a level that is acceptable to the patients. The fan control unit must be placed in a position where it is not easy for patients or health care workers to tamper with it.

To use a fan system that simply extracts air from a room into a ceiling void is an exercise in futility and a incubator for bacteria, if the air is not removed from the ceiling void.

To undercut doors is a cheap method commonly used with air conditioning installations, but this does not mean it is a silver bullet. It extracts infected air into passages, many times used as waiting areas and other populated areas.

This is one of the reasons why this type of air conditioning or ventilation installation is called a conduit for infection.

It is important to install the ceiling fan in a position where it creates the best air movement, even if it is next to a UVGI unit. The UVGI output near the unit is in any case high enough to most probably
deactivate TB bacteria with the first pass. Care must be taken to ensure that the fan position does not create a stroboscopic effect with the light fitting or the UVGI unit.

The infection must be deactivated or removed as near as possible to the source. Therefore only designers properly versed and experienced in positive and negative pressure design should be used for the design of airflow installations.

For how "slow is slow" I can only say "it all depends", because individuals do not all experience the same affect when the moving air touch their body parts.

My perception for a properly designed upper volume UVGI installation is that the air movement created by ceiling fans is slow enough if it is generally acceptable to the patients. The fan direction can be reversed for winter and summer environmental conditions.

Dries Meyer. Independent Consultant.

Dear Dries,

As moderator, I need to interject a couple of points. First, there is now a fair amount of repetition on this topic and we are risk of continuing this thread too long. Not everyone on GHDonline wants to continue to read about fan speed. Second, as a group we are better served by data than by opinion, so please try to substantiate what you write with data. Thirdly, I need to correct a few points, below.

The effective UV dose is expressed as the "Z value" which is the decrease in natural log of the kill ratio of numbers of colonies divided by the UV dose. See the ratio below, if the slide transmits, or in words it is the natural log of the kill rate for a certain microbial species divided by the UV dose. To be relevant to upper room UVGI, that measurement must be taken in air where nearly naked infectious droplet nuclei are extremely vulnerable, not on surfaces, where organisms can clump together or be covered by a fluid layer. There have been many studies of Z for TB using laboratory and clinical strains and they are similar as shown in the slide below ...

Dear Dries,

As moderator, I need to interject a couple of points. First, there is now a fair amount of repetition on this topic and we are risk of continuing this thread too long. Not everyone on GHDonline wants to continue to read about fan speed. Second, as a group we are better served by data than by opinion, so please try to substantiate what you write with data. Thirdly, I need to correct a few points, below.

The effective UV dose is expressed as the "Z value" which is the decrease in natural log of the kill ratio of numbers of colonies divided by the UV dose. See the ratio below, if the slide transmits, or in words it is the natural log of the kill rate for a certain microbial species divided by the UV dose. To be relevant to upper room UVGI, that measurement must be taken in air where nearly naked infectious droplet nuclei are extremely vulnerable, not on surfaces, where organisms can clump together or be covered by a fluid layer. There have been many studies of Z for TB using laboratory and clinical strains and they are similar as shown in the slide below - ranging from 33 - 48 - never mind the units. For the test organism, Serratia marcesens, for example, which is much more vulnerable, the Z is 214 or about 6 times more vulnerable than TB. The Penn State values published are mostly surface kill numbers and not relevant to upper room UVGI.




There is nothing magic about 10 uW/cm2, since effective inactivation dose is always a matter of exposure duration and intensity. Radiation as little as 1 uW/cm2 can be effective if the exposure is long enough. As Dries says, however, it would be great to kill organisms on one or at most a few passes into the upper room zone so as to minimize exposure to infection in the lower room. It is all complicated by the gradient of UV produced by fixtures in the upper room, whether wall or ceiling mounted. Organisms passing close to the fixture are immediately killed, but you can only kill them once, and a lot of that UV energy is "overkill" in that region, but necessary to generate an upper room "kill zone" in a large percentage of the upper room - much of it progressively lower intensity - as light spreads it decreases by the square of the distance. The notion expressed by Dries of "weakening" may or may not be true. UV causes DNA damage (and damage to other proteins). Lethal mutations are just that, and in theory sublethal mutations can be repaired. We experience mutations all the time and repair most of them. Whether upper room UV killing in rooms is "all or none" or cumulative is unclear and may not be too important for practical application.

All of that said, in the Air Facility in Witbank, using an off the shelf slow paddle fan and as much UV in the upper room as we could safely generate with two UV wall fixtures in each 2-bed room, we obtained 80% efficacy against human generated TB as measured by quantitative GP air sampling. The fixtures were placed "by eye" based on experience and we aimed for comfort levels of air movement, with the fans drawing up. In my view, 80% efficacy is probably about as good as one can expect under real hospital conditions. In some cases, coughed droplet nuclei were undoubtedly captured by the exhaust system before any UV exposure occurred. No air disinfection strategy is 100% since any method only kills a portion of the number of organisms present. In a much longer hospital study in Peru, Escombe obtrained 73% efficacy, so in the same range.

Summary of this thread: we need well designed UV fixtures to safely and efficiently deliver high intensity UV into the upper room, and we need room air mixing, ideally with a slow paddle fan that is considerate of patient comfort. We strongly suggest not using UVGI without an air mixing strategy. The details of air mixing may not be that critical within broad limits, as long as occupants are comfortable.

Unless there are NEW points or corrections, I would like to bring this discussion to a close.

Ed Nardell, moderator.

Dear Ed,
Thanks for the reply.

When will the Witbank report be published. We need the results urgently in the RSA and I am sure it will be of help in most other countries.

Regards,
Dries Meyer.

I am adding a slide presentation on upper room UVGI, given to the Am Soc of Photobiology. The 13th slide is about the Z value, that is, the susceptibility of microorganisms to UVGI.

Hello All,

I now have a related question, let me know if I should post it as a separate discussion.

As I mentioned earlier, we will be installing approximately 600 upper UVGI fixtures (3 TB inpatient hospitals, and about 30 ambulatory TB treatment locations). It may not be feasible to install the same amount of ceiling/paddle fans. So, if I need to prioritize which locations receive fans, I need to develop some sort of criteria. My thoughts so far are to use infectiousness, followed by resistance pattern. For example, highest priority to diagnostic locations (TB doctors’ offices, xray etc) followed by resistance, XDR, MDR, PDR etc. However, in many of our ambulatory locations there is no segregation by resistance, and although the patients there are all on treatment, this treatment is sometimes initiated in these ambulatory locations and therefore we have a lot of mixing between infectious and non infectious patients with various resistance patterns (segregation by scheduling patients to come at certain times of the day is also not possible). Any thoughts on how to prioritize which locations receive a fan?
Susan Adolph,
ICO Uzbekistan/Tajikistan
MSF

Susan, please re-post as "Priorities for UVGI use in high-burden settings" I am concerned that many readers will not even open yet another posts on fans, per se.

Ed

Susan do you have an e mail address that you can be contacted on. rgds. Paul.

Dear all,
Can I suggest that we have a wrap up on this very relevant discussion (Ed? Paul? some one else?), as the multiplication of messages makes the whole topic finally very confusing....because of pros and cons etc...
I would suggest that someone summarizes the topic for us
Thanks a lot for this
Have a great day
Francoise

Great suggestion . . . We can have a summary position drafted regarding this string of discussion, allow a short time for comment, and then deal with additional topics. And, we would request follow discussions as Susan and others implement UVGI.



Regards,

Paul J

--------------------------
Sent from my BlackBerry . . . Please excuse my fumbling thumbs!

Dear All,

Before giving consideration to any engineering measures and discussing their (relative) efficacy at length in details not always understandable, I would imagine that ensuring proper separation of patients is the must and funds should be dedicated to it at the first place. UVGI appears somehow as damage control in the context of Uzbekistan/Tajikistan and I am very doubtful on their real efficacy in these contexts.

Best wishes,

Philippe Creac'h

Dear Edward,
I could not find the presentation you mentioned in the message below. How
can I get it?

You click on the link to GHDonline and will see the attachment there to this discussion and you click on it there. I have asked the administrator of GHDonline to repost the document as a PDF to protect it from being changed. One hates to see slides show up elsewhere modified to make some other point, or out of context. It could be in transition. Wait a day or two before looking for it and it should be there. The slide that I was referring to is actually slide #14, not 13.

Ed

Edward A. Nardell, MD
Associate Professor
Harvard Medical School (Medicine; Global Health and Social Medicine)
Harvard School of Public Health (Environmental Health; Immunology and Infectious Diseases)

Brigham and Women's Hospital
Division of Global Health Equity
FXB Building, 709c
651 Huntington Ave.
Boston, MA 02115

617 432-6937 617 877-9412 (Cell)
(preferred) or

Thank you very much