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Natural ventilation for the prevention of airborne contagion.

Escombe AR, Oeser CC, Gilman RH, Navincopa M, Ticona E, Pan W, Martínez C, Chacaltana J, Rodríguez R, Moore DA, Friedland JS, Evans CA - PLoS Med. (2007)

Bottom Line: These rooms were compared with 12 mechanically ventilated negative-pressure respiratory isolation rooms built post-2000.We found that opening windows and doors provided median ventilation of 28 air changes/hour (ACH), more than double that of mechanically ventilated negative-pressure rooms ventilated at the 12 ACH recommended for high-risk areas, and 18 times that with windows and doors closed (p < 0.001).In settings where respiratory isolation is difficult and climate permits, windows and doors should be opened to reduce the risk of airborne contagion.

View Article: PubMed Central - PubMed

Affiliation: Department of Infectious Diseases & Immunity, Imperial College London, London, United Kingdom. rod.escombe@imperial.ac.uk

ABSTRACT

Background: Institutional transmission of airborne infections such as tuberculosis (TB) is an important public health problem, especially in resource-limited settings where protective measures such as negative-pressure isolation rooms are difficult to implement. Natural ventilation may offer a low-cost alternative. Our objective was to investigate the rates, determinants, and effects of natural ventilation in health care settings.

Methods and findings: The study was carried out in eight hospitals in Lima, Peru; five were hospitals of "old-fashioned" design built pre-1950, and three of "modern" design, built 1970-1990. In these hospitals 70 naturally ventilated clinical rooms where infectious patients are likely to be encountered were studied. These included respiratory isolation rooms, TB wards, respiratory wards, general medical wards, outpatient consulting rooms, waiting rooms, and emergency departments. These rooms were compared with 12 mechanically ventilated negative-pressure respiratory isolation rooms built post-2000. Ventilation was measured using a carbon dioxide tracer gas technique in 368 experiments. Architectural and environmental variables were measured. For each experiment, infection risk was estimated for TB exposure using the Wells-Riley model of airborne infection. We found that opening windows and doors provided median ventilation of 28 air changes/hour (ACH), more than double that of mechanically ventilated negative-pressure rooms ventilated at the 12 ACH recommended for high-risk areas, and 18 times that with windows and doors closed (p < 0.001). Facilities built more than 50 years ago, characterised by large windows and high ceilings, had greater ventilation than modern naturally ventilated rooms (40 versus 17 ACH; p < 0.001). Even within the lowest quartile of wind speeds, natural ventilation exceeded mechanical (p < 0.001). The Wells-Riley airborne infection model predicted that in mechanically ventilated rooms 39% of susceptible individuals would become infected following 24 h of exposure to untreated TB patients of infectiousness characterised in a well-documented outbreak. This infection rate compared with 33% in modern and 11% in pre-1950 naturally ventilated facilities with windows and doors open.

Conclusions: Opening windows and doors maximises natural ventilation so that the risk of airborne contagion is much lower than with costly, maintenance-requiring mechanical ventilation systems. Old-fashioned clinical areas with high ceilings and large windows provide greatest protection. Natural ventilation costs little and is maintenance free, and is particularly suited to limited-resource settings and tropical climates, where the burden of TB and institutional TB transmission is highest. In settings where respiratory isolation is difficult and climate permits, windows and doors should be opened to reduce the risk of airborne contagion.

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Related in: MedlinePlus

Measurement of VentilationIllustrative carbon dioxide (CO2) concentration-decay experiment demonstrating a rapid rise in CO2 concentration during initial release to a peak of 6,000 parts/million (ppm) followed by slow decay calculated as 0.5 ACH until the windows and doors were opened. After windows and doors were opened, CO2 concentrations fell rapidly, indicating a calculated ventilation rate of 12 ACH. Repeated experiments of this type defined the effect of architectural and environmental variables on natural ventilation.
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pmed-0040068-g001: Measurement of VentilationIllustrative carbon dioxide (CO2) concentration-decay experiment demonstrating a rapid rise in CO2 concentration during initial release to a peak of 6,000 parts/million (ppm) followed by slow decay calculated as 0.5 ACH until the windows and doors were opened. After windows and doors were opened, CO2 concentrations fell rapidly, indicating a calculated ventilation rate of 12 ACH. Repeated experiments of this type defined the effect of architectural and environmental variables on natural ventilation.

Mentions: Changes in CO2 concentration were measured in each room. A characteristic pattern was observed of slow CO2 concentration-decay with windows and doors closed, which markedly increased on opening windows and doors. Figure 1 shows a typical concentration-decay curve, demonstrating the rapid increase in carbon dioxide removal by ventilation when windows and doors were opened. Such data was obtained for all rooms measured. For all naturally ventilated facilities, opening windows and doors provided median absolute ventilation of 2,477 m3/h, more than six times the 402 m3/h calculated for mechanically ventilated rooms at 12 ACH, and twenty times the 121 m3/h with windows/doors closed (all p < 0.001). The corresponding ACH were 28 versus 12 versus 1.5, respectively, and absolute ventilation per person was 1,053 m3/h versus 374 m3/h versus 55 m3/h, respectively (all p < 0.001).


Natural ventilation for the prevention of airborne contagion.

Escombe AR, Oeser CC, Gilman RH, Navincopa M, Ticona E, Pan W, Martínez C, Chacaltana J, Rodríguez R, Moore DA, Friedland JS, Evans CA - PLoS Med. (2007)

Measurement of VentilationIllustrative carbon dioxide (CO2) concentration-decay experiment demonstrating a rapid rise in CO2 concentration during initial release to a peak of 6,000 parts/million (ppm) followed by slow decay calculated as 0.5 ACH until the windows and doors were opened. After windows and doors were opened, CO2 concentrations fell rapidly, indicating a calculated ventilation rate of 12 ACH. Repeated experiments of this type defined the effect of architectural and environmental variables on natural ventilation.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC1808096&req=5

pmed-0040068-g001: Measurement of VentilationIllustrative carbon dioxide (CO2) concentration-decay experiment demonstrating a rapid rise in CO2 concentration during initial release to a peak of 6,000 parts/million (ppm) followed by slow decay calculated as 0.5 ACH until the windows and doors were opened. After windows and doors were opened, CO2 concentrations fell rapidly, indicating a calculated ventilation rate of 12 ACH. Repeated experiments of this type defined the effect of architectural and environmental variables on natural ventilation.
Mentions: Changes in CO2 concentration were measured in each room. A characteristic pattern was observed of slow CO2 concentration-decay with windows and doors closed, which markedly increased on opening windows and doors. Figure 1 shows a typical concentration-decay curve, demonstrating the rapid increase in carbon dioxide removal by ventilation when windows and doors were opened. Such data was obtained for all rooms measured. For all naturally ventilated facilities, opening windows and doors provided median absolute ventilation of 2,477 m3/h, more than six times the 402 m3/h calculated for mechanically ventilated rooms at 12 ACH, and twenty times the 121 m3/h with windows/doors closed (all p < 0.001). The corresponding ACH were 28 versus 12 versus 1.5, respectively, and absolute ventilation per person was 1,053 m3/h versus 374 m3/h versus 55 m3/h, respectively (all p < 0.001).

Bottom Line: These rooms were compared with 12 mechanically ventilated negative-pressure respiratory isolation rooms built post-2000.We found that opening windows and doors provided median ventilation of 28 air changes/hour (ACH), more than double that of mechanically ventilated negative-pressure rooms ventilated at the 12 ACH recommended for high-risk areas, and 18 times that with windows and doors closed (p < 0.001).In settings where respiratory isolation is difficult and climate permits, windows and doors should be opened to reduce the risk of airborne contagion.

View Article: PubMed Central - PubMed

Affiliation: Department of Infectious Diseases & Immunity, Imperial College London, London, United Kingdom. rod.escombe@imperial.ac.uk

ABSTRACT

Background: Institutional transmission of airborne infections such as tuberculosis (TB) is an important public health problem, especially in resource-limited settings where protective measures such as negative-pressure isolation rooms are difficult to implement. Natural ventilation may offer a low-cost alternative. Our objective was to investigate the rates, determinants, and effects of natural ventilation in health care settings.

Methods and findings: The study was carried out in eight hospitals in Lima, Peru; five were hospitals of "old-fashioned" design built pre-1950, and three of "modern" design, built 1970-1990. In these hospitals 70 naturally ventilated clinical rooms where infectious patients are likely to be encountered were studied. These included respiratory isolation rooms, TB wards, respiratory wards, general medical wards, outpatient consulting rooms, waiting rooms, and emergency departments. These rooms were compared with 12 mechanically ventilated negative-pressure respiratory isolation rooms built post-2000. Ventilation was measured using a carbon dioxide tracer gas technique in 368 experiments. Architectural and environmental variables were measured. For each experiment, infection risk was estimated for TB exposure using the Wells-Riley model of airborne infection. We found that opening windows and doors provided median ventilation of 28 air changes/hour (ACH), more than double that of mechanically ventilated negative-pressure rooms ventilated at the 12 ACH recommended for high-risk areas, and 18 times that with windows and doors closed (p < 0.001). Facilities built more than 50 years ago, characterised by large windows and high ceilings, had greater ventilation than modern naturally ventilated rooms (40 versus 17 ACH; p < 0.001). Even within the lowest quartile of wind speeds, natural ventilation exceeded mechanical (p < 0.001). The Wells-Riley airborne infection model predicted that in mechanically ventilated rooms 39% of susceptible individuals would become infected following 24 h of exposure to untreated TB patients of infectiousness characterised in a well-documented outbreak. This infection rate compared with 33% in modern and 11% in pre-1950 naturally ventilated facilities with windows and doors open.

Conclusions: Opening windows and doors maximises natural ventilation so that the risk of airborne contagion is much lower than with costly, maintenance-requiring mechanical ventilation systems. Old-fashioned clinical areas with high ceilings and large windows provide greatest protection. Natural ventilation costs little and is maintenance free, and is particularly suited to limited-resource settings and tropical climates, where the burden of TB and institutional TB transmission is highest. In settings where respiratory isolation is difficult and climate permits, windows and doors should be opened to reduce the risk of airborne contagion.

Show MeSH
Related in: MedlinePlus