Ever since the 2007 publication of Rod Escombe's measurements of natural ventilation rates in hospitals in Lima, Peru, (Natural Ventilation for the Prevention of Airborne Contagion, February 2007: http://medicine.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pmed.0040068&ct=1) there has been an outpouring of enthusiasm for this approach.
The study in Lima, a costal city, showed very high estimated ventilation rates with windows open, much higher than in normally possible by mechanical ventilation systems. In published commentary, Hal Levin urged caution in not over interpreting those theoretical results.
Although I think natural ventilation has an important role to play, it is mostly a design feature, i.e, in suitable climates, the use of outdoor covered corridors, waiting areas, sputum induction areas, and exhaust stacks etc. I am less enthused about depending on natural ventilation for air disinfection in rooms simply because conditions in most locations vary from minute to minute, night and day, and by season. Neither the direction of airflow nor the numbers of air changes can be assured, but depend on prevailing climatic conditions. Even in Africa windows are often shut tight at night because of low night temperatures and for security.
Finally, Li published a meta analysis of the literature of ventilation and airborne infection, pointing out that while an association is clearly evident, there is no good basis for recommending specific levels of ventilation in specific settings.
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Escombe AR, Moore DAJ, Friedland JS, Evans CA, Gilman RH (2007) Natural Ventilation for Prevention of Airborne Contagion: Authors' Reply. PLoS Med 4(5): e195
<http://medicine.plosjournals.org/perlserv/?request=read-response&doi=10.1371/journal.pmed.0040068>
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Li Y, Leung GM, Tang JW, Yang X, Chao CY, Lin JZ, Lu JW, Nielsen PV, Niu J, Qian H, Sleigh AC, Su HJ, Sundell J, Wong TW, Yuen PL. (2007) Role of ventilation in airborne transmission of infectious agents in the built environment - a multidisciplinary systematic review. Indoor Air, Vol. 17, Number 1, pp. 2-18(17)
<http://www.ingentaconnect.com/content/mksg/ina/2007/00000017/00000001/art00002>
Controversies in TB Transmission Control: How important is natural ventilation to the spread of tuberculosis?
started on 2008-Jul-14 by Edward Nardell, MD
Keywords:
Engineering Controls
