TB Infection Control

Good Morning

You are correct 0.2 micro watts if the person lays on their back looking at
it for an 8 hour period.
0.4 micro watts is more realistic for most environment's e.g clinics and
hospital staff.
Receptionists and booking clerks are also safe as they look down at their
work and not at the UV lights.

Meters are available in South Africa i am an agent for them they are made to
international standards
very easy to use. The meter is a Goldilux.

The way i have found to work for me is to place a few discrete marks on the
ceiling as reference points and revisit then and log value date and time
once a month.
This only takes a few minutes.



Kind Regards,

Robert Spiteri
Ozone Purification Technology
Aerobiological Tech-Eng
Cell: 082 400 9291
Tell: 011 462 5525
Fax: 086 607 6638
www.uvozone.co.za

the marks on the ceiling are to monitor aging of the lamps

safety is measures at 1.8 meters from the floor

regards
rob

Dear Andiyanto,
 
It is critical to use accurate UV-C meter to measure 254 nm UV-C irradiance at low levels (as low as 0,1 uW/cm2 is enough) for both effective and safe upper room UV fixtures installation and maintenance.
 
I would recommend the German meter:
 
1. UV-C meter itself: Gigahertz-Optik X9 11 LS UV-C Meter to measure UV-C irradiance and dose  with UV-3781-4 detector. Functions : CW, dose, peak, run/Stop, RS232; ITT type socket.Battery and manual,Direct reading in µW/cm². Part number : 100559 Cost ~ $655
 
 2. UV-3718-4 Radiometric Detector to measure UV C irradiance at 254 nm Calibration in W/cm² at 254 nm. Part number 100560. Cost ~ $983

3. BHO-05 Option: Hard case to carry and store the X9 11 & detector. Part number 100020 (optional and not quite useful). Cost ~ $62

www.gigahertz-optik.de

All gigahertz instrumentation must be serviced and recalibrated at GIGAHERTZ OPTIC main facility in Puchheim (MUNICH). K-X9n-C Meter Calibration= US$77
BI-ANNUAL RECALIBRATION RECOMMENDED
K-UV3718-S Detector Calibration= US$318 Annual recalibration is recommended.

The equipment is not cheap, but in practice we have realized it helps to actually save resources on UV-C lamps replacement: now we can effectively use most of them ...

Dear Andiyanto,
 
It is critical to use accurate UV-C meter to measure 254 nm UV-C irradiance at low levels (as low as 0,1 uW/cm2 is enough) for both effective and safe upper room UV fixtures installation and maintenance.
 
I would recommend the German meter:
 
1. UV-C meter itself: Gigahertz-Optik X9 11 LS UV-C Meter to measure UV-C irradiance and dose  with UV-3781-4 detector. Functions : CW, dose, peak, run/Stop, RS232; ITT type socket.Battery and manual,Direct reading in µW/cm². Part number : 100559 Cost ~ $655
 
 2. UV-3718-4 Radiometric Detector to measure UV C irradiance at 254 nm Calibration in W/cm² at 254 nm. Part number 100560. Cost ~ $983

3. BHO-05 Option: Hard case to carry and store the X9 11 & detector. Part number 100020 (optional and not quite useful). Cost ~ $62

www.gigahertz-optik.de

All gigahertz instrumentation must be serviced and recalibrated at GIGAHERTZ OPTIC main facility in Puchheim (MUNICH). K-X9n-C Meter Calibration= US$77
BI-ANNUAL RECALIBRATION RECOMMENDED
K-UV3718-S Detector Calibration= US$318 Annual recalibration is recommended.

The equipment is not cheap, but in practice we have realized it helps to actually save resources on UV-C lamps replacement: now we can effectively use most of them much longer based on actual measured UV-C levels.

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

PPlease don't print this e-mail unless you really need to. Thank you!

I agree with Gregory on the Gigahertz Optic X911UV-C meter and the
detector head. The important part of the meter is the detector head. It
must be cosine corrected and solar blind. Do not buy a UV-C meter if it
is not cosine corrected and solar blind.

I am not promoting Gigahertz Optic meters but I do a lot of
experimenting, development of UVGI units and testing work and since I
purchased a Gigahertz Optic found that it was very user friendly and
because it is cosine corrected and solar blind, the test results were
more accurate than any of the meters I previously used.

Dries Meyer.

I would like to emphasize the point that Robert made about the 0.2 Uw/cm2 8-hr exposure number from the CDC/NIOSH report cited. It is really important to know that 0.2 is NOT an exposure limit. The 8-hr exposure limit is 6.0 mJ/cm2, which is a UV dose, not irradiance. As Robert said, if you stare at the fixture at the point where 0.2 uW/cm2 is measured for 8 hrs, you will have received the 6.0 mJ/cm2 dose for that 8 hr period. There is some disagreement on whether you can be exposed for another 6.0 mJ/cm2 by staring at the fixture for the next 8 hrs, and another for the next 8 hrs, etc - for room occupants in a room for 24 hrs. Usually this is a moot point with well designed fixtures exposure is usually far less. The big unknown is time-motion of the occupant since rarely is actual eye exposure at the peak measured irradiance for 8 hrs. Not only do people not stare at the fixture, they move around, close eyes, and the shape of the head protects the eyes from direct exposure to sun ...

I would like to emphasize the point that Robert made about the 0.2 Uw/cm2 8-hr exposure number from the CDC/NIOSH report cited. It is really important to know that 0.2 is NOT an exposure limit. The 8-hr exposure limit is 6.0 mJ/cm2, which is a UV dose, not irradiance. As Robert said, if you stare at the fixture at the point where 0.2 uW/cm2 is measured for 8 hrs, you will have received the 6.0 mJ/cm2 dose for that 8 hr period. There is some disagreement on whether you can be exposed for another 6.0 mJ/cm2 by staring at the fixture for the next 8 hrs, and another for the next 8 hrs, etc - for room occupants in a room for 24 hrs. Usually this is a moot point with well designed fixtures exposure is usually far less. The big unknown is time-motion of the occupant since rarely is actual eye exposure at the peak measured irradiance for 8 hrs. Not only do people not stare at the fixture, they move around, close eyes, and the shape of the head protects the eyes from direct exposure to sun and to upper room UV. As a result, in First, M. W.; Weker, R. A.; Yasui, S., and Nardell, E. A. Monitoring human exposures to upper-room germicidal ultraviolet irradiation. J Occup Environ Hyg. 2005 May; 2(5):285-92, we showed that patients and nurses in a facility with poorly designed UV fixtures that put out up to 1.0 uW eye level irradiance was perfectly safe for room occupants. Not only were there no complaints by patients in these rooms for most of 24 hours, but a portable meter around their necks registered no more than 1/3 of the 6.0 mJ/8-hr limit. Rarely have we seen eye complaints due to properly installed, well-designed UV fixtures. In a large study in homeless shelters, the only eye complaint was from the occupant of the top bunk of a double bunk bed that had been placed near a UV wall fixture, so exposure was intense. See: Nardell EA, Bucher SJ, Brickner PW, Wang C, Vincent RL, Becan-McBride K, James MA, Michael M, Wright JD. Safety of upper-room ultraviolet germicidal air disinfection for room occupants: results from the Tuberculosis Ultraviolet Shelter Study. Public Health Rep. 2008 Jan-Feb;123(1):52-60.

Bottom line - the exact exposure limit depends on how occupants use the room, that is, the time-motion factor. As Robert stated, 0.4 uW is an extremely safe and conservative target, but even 0.6 may be safe in corridors where occupants are highly unlikely to stare at fixtures for even 2 hours continuously. As noted, in a hospital setting we have had no complaints for decades by nurses and patients where peak irradiance was as high as 1.0 uW. If peak eye-level irradiance measurements are between 0.4 and 1.0 uW it may be reasonable to permit occupancy and to closely monitor occupants for eye irritation symptoms. If there are none, one can assume that the actual DOSE is under the 6.0 mJ/8-hr exposure limit. Such an exposure trial is essential a time-motion assessment. The lack of symptoms means that human eyes are not exposed in actuality to the peak meter levels.

Ed

Edward A. Nardell, MD (note: new address below, effective immediately)
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
Partners In Health
461 Huntington Avenue, 3A-03
Boston, MA 02115
 
617 432-2080 (academic office)   617 877-9412 (cell)

Many thank
For putting it all into perspective
Regards
Rob

Thanks to all your response. I am curious how these exposure limit is actually enforced in practice. Or is the table in the document not meant for enforecement? Although it is not possible, it is not a simple task to monitor the total exposure of a particular occupant as well. Perhaps it is a good input to discuss with NIOSH on the exact meeting of this document?

Would the consideration change when the UVGI is put in a patient room where the patient stays for 24 hours with limited motion?

Would a meter with 0.1 uW/cm2 resolution be useful in this case then? Looking at how measurement of 0.4 uW/cm2 can easily mean 0.3-0.4 uW/cm2 due to the resolution (accuracy can be good but it will also limited by the resolution).

What would be the consensus acceptable for the limit of exposure then? 0.4 uW/cm2? For both healthcare worker and patient? Then this limit can be used to determine the specifications of the appropriate meter.

Thanks Grigory and Dries. I will contact the company. I recalled in the past I emailed them and has not had response! Edward suggested ILT as ...

Thanks to all your response. I am curious how these exposure limit is actually enforced in practice. Or is the table in the document not meant for enforecement? Although it is not possible, it is not a simple task to monitor the total exposure of a particular occupant as well. Perhaps it is a good input to discuss with NIOSH on the exact meeting of this document?

Would the consideration change when the UVGI is put in a patient room where the patient stays for 24 hours with limited motion?

Would a meter with 0.1 uW/cm2 resolution be useful in this case then? Looking at how measurement of 0.4 uW/cm2 can easily mean 0.3-0.4 uW/cm2 due to the resolution (accuracy can be good but it will also limited by the resolution).

What would be the consensus acceptable for the limit of exposure then? 0.4 uW/cm2? For both healthcare worker and patient? Then this limit can be used to determine the specifications of the appropriate meter.

Thanks Grigory and Dries. I will contact the company. I recalled in the past I emailed them and has not had response! Edward suggested ILT as well but I am having quite a long drawn discussion with ILT on their device due the resolution limitation.


Best regards,
Andiyanto Sutandar
Biorisk Consultant
Det Norske Veritas Pte. Ltd.

Dear Andiyanto,

You have missed some of my points. The exposure limit is not enforced because it is impossible to predict time-motion of occupants in rooms and figure out exact exposure unless you do personal monitoring with a special meter as we did in the paper that I cited. If there are no eye complaints, you are under 6.0 mJ/cm2. If there are eye complaints, you are over that limit. Shooting for 0.4 uW/cm2 is a conservative target for peak irradiance. The exact number is not critical so your 0.1 meter should be OK, if not ideal. As our study showed, even with older fixtures that put out peak eye-level irradiance in the order of 1.0 uW/cm2, patients in the room 24 hrs had no complaints. There is a lot of wiggle room in the TLV because of time-motion patterns. Patients lay in bed, close their eyes, etc, etc, all reducing actual exposure.

Upper room UVGI is incredibly safe if properly designed and installed. Except for workers climbing up into the direct UV field and getting accidental eye exposure, the worst that can happen is mild eye irritation from a poor installation.

Ed ...

Dear Andiyanto,

You have missed some of my points. The exposure limit is not enforced because it is impossible to predict time-motion of occupants in rooms and figure out exact exposure unless you do personal monitoring with a special meter as we did in the paper that I cited. If there are no eye complaints, you are under 6.0 mJ/cm2. If there are eye complaints, you are over that limit. Shooting for 0.4 uW/cm2 is a conservative target for peak irradiance. The exact number is not critical so your 0.1 meter should be OK, if not ideal. As our study showed, even with older fixtures that put out peak eye-level irradiance in the order of 1.0 uW/cm2, patients in the room 24 hrs had no complaints. There is a lot of wiggle room in the TLV because of time-motion patterns. Patients lay in bed, close their eyes, etc, etc, all reducing actual exposure.

Upper room UVGI is incredibly safe if properly designed and installed. Except for workers climbing up into the direct UV field and getting accidental eye exposure, the worst that can happen is mild eye irritation from a poor installation.

Ed

Edward A. Nardell, MD (note: new address below, effective immediately)
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
Partners In Health
641 Huntington Avenue, 3A-03
Boston, MA 02115
 
617 432-2080 (academic office)   617 877-9412 (cell)

Thanks again

For clearing up what seems to be a large stumbling block in this area of
UVGI

It is so important to understand when taking readings that we understand
what we measuring
When measuring UVC, is it a true reading of UVC or is it influenced by the
lights surrounding it?

Measurements taken at fixed points with UV ON AND UV OFF will give the same
result. This is due to the fact that ambient lighting affects some meters.

My experience has shown that taking readings at night with the illumination
lights off gives me an accurate result (not so during the day)

Regards
Rob

If a UV-C meters detector head is affected by wave lengths other than
253.7 (254) nm it can not be a true UV-C meter, whether it is used in
daylight or at night time. If it is not correct in daylight. how can it
be correct at night ? It is still the same detector head with a defect.

The detector head must at all times be able to isolate the UV-C
radiation and exclude all other out of band signals. That is why it must
be cosine corrected. It is important to maintain low measurement
uncertainties and have a clear field of view. It must also have a solar
blind photo diode detector with UV stability and a solar blind spectral
sensitivity characteristic.

In the RSA the MRC established a peak irradiance of 0.4µW/cm² at a
height of 1.8m (6ft) above floor level. This is a safe and generally
accepted peak irradiation level.

UVGI units should be designed to comply to this requirement. It is also
practical to design a unit that is safe at 1.8m because it will still be
safe at 2.7m or higher. For practical purposes the same type of unit ...

If a UV-C meters detector head is affected by wave lengths other than
253.7 (254) nm it can not be a true UV-C meter, whether it is used in
daylight or at night time. If it is not correct in daylight. how can it
be correct at night ? It is still the same detector head with a defect.

The detector head must at all times be able to isolate the UV-C
radiation and exclude all other out of band signals. That is why it must
be cosine corrected. It is important to maintain low measurement
uncertainties and have a clear field of view. It must also have a solar
blind photo diode detector with UV stability and a solar blind spectral
sensitivity characteristic.

In the RSA the MRC established a peak irradiance of 0.4µW/cm² at a
height of 1.8m (6ft) above floor level. This is a safe and generally
accepted peak irradiation level.

UVGI units should be designed to comply to this requirement. It is also
practical to design a unit that is safe at 1.8m because it will still be
safe at 2.7m or higher. For practical purposes the same type of unit
should be installed in the same facility. The trend, especially in the
RSA, is to design a unit for 2.7m or higher. These units are then
installed at levels of 2.4m and the irradience then exceeds the
0.4µW/cm² level. The unit output is then "corrected" by installing
internal louvres which block and lower the UV-C irradience to a level
where the unit is ineffective. I have seen Goniometer test results
clearly indicating this. It the internal louvres still dont work,
titanium dioxide mixed with water is sprayed onto the internal
reflectors to absorb UV-C. The UV-C output of the unit is thus lowered,
the Iso-irradiance volume is smaller, and therefore the efficacy is
lowered. To my knowledge titanium dioxide has never been approved for
inclusion by the CDC for upper volume air disinfection. The titanium
dioxide dries out and become powder again and it is removed by air
movement. I do not know what the effect is when the titanium oxide is
inhaled by humans, even in minute quantities.

Dries Meyer.

Dear Ed,

I understood the difficulty of determining the total exposure and as you said, unless there is a big complaint on occupational health side, it is likely to be safe within the expected limit. As mentioned, user would probably still want to have a figure to work out what's considered safe.

I do realise that there are plenty of so-called UVC meter although the spectral peak can be in any wavelength. There are quite a number with peak at 254 nm with bell shaped spectral response distribution in the region of 200 - 300 nm in general. This is expected as it is not possible to have perfect filter at a single wavelength. This also translate to a fact that measured 0.2 uW/cm2 is a combination of irradiation at the sensor's response curve and not just 254 nm so the 1.0 uW/cm2 may easily be 0.5 uW/cm2 in terms of real 254 nm. Not too sure whether the calculation really address just 254 nm exact wavelength radiation. Then again, as mentioned by many of you, the key is not to have occupational health issue.

So I think as a conclusion, may I ...

Dear Ed,

I understood the difficulty of determining the total exposure and as you said, unless there is a big complaint on occupational health side, it is likely to be safe within the expected limit. As mentioned, user would probably still want to have a figure to work out what's considered safe.

I do realise that there are plenty of so-called UVC meter although the spectral peak can be in any wavelength. There are quite a number with peak at 254 nm with bell shaped spectral response distribution in the region of 200 - 300 nm in general. This is expected as it is not possible to have perfect filter at a single wavelength. This also translate to a fact that measured 0.2 uW/cm2 is a combination of irradiation at the sensor's response curve and not just 254 nm so the 1.0 uW/cm2 may easily be 0.5 uW/cm2 in terms of real 254 nm. Not too sure whether the calculation really address just 254 nm exact wavelength radiation. Then again, as mentioned by many of you, the key is not to have occupational health issue.

So I think as a conclusion, may I say as a consensus, 0.4 - 1 uW/cm2 is considered acceptable irradiation at 1.8 m and a meter with 0.1 uW/cm2 resolution is commonly used without an issue?

Thanks This works for me
Regards
Rob

Dear Andiyanto,
 
Regarding 0.4 - 1 uW/cm2 range I would recommend flexible approach to take into account the occupancy of the particular room. For example for patient room, staff office, laboratory where people can stay for hours or longer -  lower levels should be acceptable, but for corridors, waiting areas where people usually stay less than 20 - 30 minutes 1 uW/cm2 at eye level is absolutely safe.
 
Regards,
 
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

PPlease don't print this e-mail unless you really need to. Thank you!

Thanks for all your input.