TB Infection Control

I think you will find the references for those estimates in the WHO document on natural ventilation. I will look for it and post it on GHDonline if it is not there already. Of course, those are guidelines for having enough opening, but the driving force is air movement, and no amount of window area guarantees that there is consistent air movement and that it is in a favorable direction. When it is not, and during cold evenings, it is good to consider a back up system, such as UVGI.

Ed Nardell

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

I agree with Edward Nardell. A big opening without any movement will give no ventilation. Even a small gap under a door, say two centimeters will allow for 3 to 5 ACH, although the speed of air will be high and you might feel a draft.
More important however, the minimal requirements set by the National Building Standards should never be ignored, they have president above guidelines.

Dear Ed, Hans and Paul,
many thanks for your replies. I did look up the WHO Natural Ventilation document, which I suggest you make available in this website as well, but unfortunately there is no reference to this ratio. I will be awaiting for yhe final reference, if you are able to find it.
Luciana

Dear All,
We have to remember that for Natural Ventilation, there are no plug in formulas that exist with empirical derivation and proof. This is still an art rather than a science. We know that air changes are required. Air dilution is a prime parameter in this. How do you ACCURATELY measure air changes with natural ventilation? The factors influencing this are many, varied and with multiple permutations. External, internal and usage factors influence the placement and size of windows. I would be very nervous of quoting a window to wall ratio without knowing the maximum no of parameters influencing the specific site over all seasonal changes.
I would prefer to recommend a some what simplistic but intuitive approach for small and simple spaces. Imagine the concerned space to be filled with smoke. If you open the correct windows, up wind and down wind, the smoke should flow out. How quickly the room clears is dependent on the factors we have to work with.
A case by case approach is required.
For complex and large projects Involve someone with experience in natural ventilation, early in the design phase.

Tariq,
Would you be so kind as to post the link to your recently completed hospital. As I recall, natural ventilation played a very important part in the design in the outdoor waiting area and within the building.
Warmest regards,
Ginny

Ginny Lipke RN, MHA, ACRN, CIC
Infection Control Practitioner & Preventionist
Division of Global HIV/AIDS (DGHA)
Center for Global Health (CGH)
Centers for Disease Control and Prevention
1600 Clifton Road, N.E.   Mailstop E-04
Atlanta, GA 30033
Tel.  1-404-639-6314
FAX 1-404-639-6499
e-mail

Hi Virginia, All,

Tariq posted his presentations from the 2010 Building Design and Engineering
Approaches to Airborne Infection Control Course that took place at the
Center of Continuing Professional Education at Harvard School of Public
Health. It may be what you are looking for... Here are the links:

- OJHA Hospital TB cetner at the Dow University of Medical Sciences TB
Isolation room
http://www.ghdonline.org/ic/resource/ojha-hospital-tb-center-at-the-dow-unive...

- The Ghauri ID Clinic MDR TB Facility
http://www.ghdonline.org/ic/resource/the-ghauri-id-clinic-mdr-tb-facility/

- Air & the Basics of Natural & Mixed Mode ventilation
http://www.ghdonline.org/ic/resource/air-the-basics-of-natural-mixed-mode-ven...

- The Design process, Design cycle, and Design briefs
http://www.ghdonline.org/ic/resource/the-design-process-design-cycle-design-b...

If the WHO natural ventilation document is not on line already, it will be posted shortly.

Paul Jensen, Grace Egos, Michael Murphy, and Gary Blackwelder just completed a PATH/USAID sponsored training for architects and engineers in Hyderabad, India. We did some ventilation and smoke tube tests in many areas of a TB hospital, including the MDR wards. As always, I was struck with the variability of airflow (volume and direction) and the meaninglessness of attaching a precise number of air changes to almost any natural ventilation situation. On the Men's ward we calculated a window to floor area (not wall area) area of 5.6%, so below the recommended 10%. This means that the room was relatively deep and there were high ceiling, and indeed, despite measureable (but variable) air flow measured at the windows, smoke released in the center of the room just hung there and slowly dispersed. Using gross estimations based on flow only (probably +/- 50%) we calculated 38 ACH - by the window. But remember - not much smoke movement away from the windows. CO2 decay would probably give a better estimate, but one would need to sample at many areas in the room to get a ...

If the WHO natural ventilation document is not on line already, it will be posted shortly.

Paul Jensen, Grace Egos, Michael Murphy, and Gary Blackwelder just completed a PATH/USAID sponsored training for architects and engineers in Hyderabad, India. We did some ventilation and smoke tube tests in many areas of a TB hospital, including the MDR wards. As always, I was struck with the variability of airflow (volume and direction) and the meaninglessness of attaching a precise number of air changes to almost any natural ventilation situation. On the Men's ward we calculated a window to floor area (not wall area) area of 5.6%, so below the recommended 10%. This means that the room was relatively deep and there were high ceiling, and indeed, despite measureable (but variable) air flow measured at the windows, smoke released in the center of the room just hung there and slowly dispersed. Using gross estimations based on flow only (probably +/- 50%) we calculated 38 ACH - by the window. But remember - not much smoke movement away from the windows. CO2 decay would probably give a better estimate, but one would need to sample at many areas in the room to get a representative idea of what is really happening (at that moment). In the female ward the ceiling was dropped and it seemed more crowded with beds because the area was much smaller. However, airflow seemed much better, possibly due to the orientation of the building, or perhaps the wind had picked up. The smaller floor area resulted in a higher window to floor area ratio of 15%, and the lower ceilings would likely give a much higher estimated ACH - we did not measure flow in this room. Higher ceilings give better dilution, but the larger room air volumes may reduce air changes per hour, depending on widow area and air flow. The smoke tube did indeed suggest much faster clearance from the center of the female ward compared to the male ward.

The lesson we learned by this field test was that natural ventilation is not necessarily intuitive. From appearances we expected the larger male ward with high ceilings to be better ventilated, but after testing we thought that the female ward was actually better. The window area to floor area ratio did seem to predict that. The other lesson is the great variability and the need to consider natural ventilation estimates on site as only a suggestion. Paul Jensen likes to classify natural ventilation no more precisely than "a little" or "a lot" and leave it at that. I think he is right.

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)

Hi Ginny,
Sophie just added the links. Best regards TAQ

But one thing about natural ventialtion - its predictabely low if windows are not opened -so the ideal desiogn is to ensure at least windows are always open (climate permiting)
And its very low cost
d

Dr Dick Menzies
Montreal Chest Institute
Room K1.24
3650 St. Urbain St.
Montreal, PQ, CANADA, H2X 2P4
Tel: 1-514-934-1934 ext 32128 or 32129
Fax: 1-514-843-2083
Can't interpret a TST? Try this web-site: www.tstin3d.com

Natural ventilation is very variable. Therefore forced air movement is required. Paddle fans, exhaust fans, roof top whrli birds, ducted air input and extraction systems etc work very well, and should be used to supplement open windows and cross flow ventilation.
Air changes is a prime parameter, however air dilution in large rooms is also a very positive factor. Brown ian movement, convection currents from body heat will move air, dilute and mix it in high volume rooms. Fans really help in this. The occupancy density of the room is also critical. We need to understand the volume of air in the room , the volume of air entering the room, the volume of air exiting the room, the volume of contaminants being generated with in the room. Can't forget the air quality outside the room.

Please add "volume of air within the room" along with the air volume entering, exiting spaces in my last mail. All said and done windows are great, but only if they are open!

Hi,

The WHO guidelines: Natural Ventilation for Infection Control in Health-Care
Settings, 2009 are available on GHDonline with a summary of the main
recommendations at this link:
http://www.ghdonline.org/ic/resource/natural-ventilation-for-infection-contro...

and directly on the WHO website in PDF at this link:
http://www.who.int/water_sanitation_health/publications/natural_ventilation.pdf

Best, Sophie