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Natural Ventilation for Infection Control in Health …

WHO Publication/GuidelinesNatural Ventilation for Infection Control in Health -Care SettingsEdited by:James Atkinson, Yves Chartier,Carmen L cia Pessoa-Silva, Paul Jensen, Yuguo Liand Wing-Hong SetoWHO Library Cataloguing-in-Publication Data: Natural Ventilation for Infection Control in Health -care Ventilation methods. 2. Air microbiology. 3. Infection Control . 4. Health facilities standards. 5. Guidelines. I. World Health 978 92 4 154785 7 (NLM classification:WX 167) World Health Organization 2009 All rights reserved. Publications of the World Health Organization can be obtained from WHO Press, World Health Organization, 20 Avenue Appia, 1211 Geneva 27, Switzerland (tel.: +41 22 791 3264; fax: +41 22 791 4857; e-mail: Requests for permission to reproduce or translate WHO publications whether for sale or for non-commercial distribution should be addressed to WHO Press, at the above address (fax: +41 22 791 4806; e-mail: The designations employed and the presentation of the material in this publication do not imply the expression of any opinion whatsoever on the part of the World Health Organization concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.))

WHO Library Cataloguing-in-Publication Data: Natural ventilation for infection control in health-care settings. 1. Ventilation — methods. 2. Air microbiology.

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Transcription of Natural Ventilation for Infection Control in Health …

1 WHO Publication/GuidelinesNatural Ventilation for Infection Control in Health -Care SettingsEdited by:James Atkinson, Yves Chartier,Carmen L cia Pessoa-Silva, Paul Jensen, Yuguo Liand Wing-Hong SetoWHO Library Cataloguing-in-Publication Data: Natural Ventilation for Infection Control in Health -care Ventilation methods. 2. Air microbiology. 3. Infection Control . 4. Health facilities standards. 5. Guidelines. I. World Health 978 92 4 154785 7 (NLM classification:WX 167) World Health Organization 2009 All rights reserved. Publications of the World Health Organization can be obtained from WHO Press, World Health Organization, 20 Avenue Appia, 1211 Geneva 27, Switzerland (tel.: +41 22 791 3264; fax: +41 22 791 4857; e-mail: Requests for permission to reproduce or translate WHO publications whether for sale or for non-commercial distribution should be addressed to WHO Press, at the above address (fax: +41 22 791 4806; e-mail: The designations employed and the presentation of the material in this publication do not imply the expression of any opinion whatsoever on the part of the World Health Organization concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.))

2 Dotted lines on maps represent approximate border lines for which there may not yet be full mention of specific companies or of certain manufacturers products does not imply that they are endorsed or recommended by the World Health Organization in preference to others of a similar nature that are not mentioned. Errors and omissions excepted, the names of proprietary products are distinguished by initial capital reasonable precautions have been taken by the World Health Organization to verify the information contained in this publication. However, the published material is being distributed without warranty of any kind, either expressed or implied. The responsibility for the interpretation and use of the material lies with the reader. In no event shall the World Health Organization be liable for damages arising from its use. The named authors alone are responsible for the views expressed in this cover photographs show Health -care facilities in (from top to bottom) Myanmar, South Africa, Peru, Nepal, Hong Kong SAR and designed by Design ONE, Canberra, AustraliaProduction and design by Biotext, CanberraiiiC o n t e n t sForeword.

3 IxAcknowledgments ..xiContributors ..xiiiConflicts of interest ..xviiExecutive summary ..xixAcronyms and definitions of terms ..xxiiiPart 1 Infection Control and Ventilation ..11 General principles of Infection The concept of isolation precaution and an historical review .. Isolation practices for Infection Control .. Isolation practices for airborne infections .. Infection Control for high-risk procedures .. Summary ..62 Concepts and types of Ventilation .. Ventilation .. What is Natural Ventilation ? .. What is mechanical Ventilation ? .. What is hybrid or mixed-mode Ventilation ? .. Assessing Ventilation performance .. Comparison of mechanical and Natural Ventilation .. Mechanical Ventilation .. Natural Ventilation .. Mechanical versus Natural Ventilation for Infection Control .. Summary ..15iv Natural Ventilation for Infection Control in Health -Care Settings3 Infection and Ventilation .

4 The association between Ventilation and Infection .. Ventilation requirements relating to airborne Infection Control .. World Health Organization recommendations relating to Natural Ventilation requirements .. Explanation of the World Health Organization recommendations .. Review and assessment of recommendations .. Summary ..24 Part 2 Designing for Natural Ventilation ..254 Understanding Natural Ventilation .. The driving forces of Natural Ventilation .. Wind pressure .. Stack (or buoyancy) pressure .. Ventilation flow rate ..305 Design and operation .. Designs for Natural Ventilation and hybrid Ventilation systems .. Natural Ventilation systems .. Hybrid (mixed-mode) Ventilation systems .. Basic design concepts for Natural Ventilation .. Climatic and other considerations in Ventilation design .. Maintaining thermal comfort .. Considerations for hot summers.

5 Considerations for winter .. Maintaining healthy indoor air quality .. Managing ambient air pollution .. External noise .. Selecting low-emission interior materials .. Humidity and mould growth .. Security and vector-borne disease spread .. High-rise considerations .. Fire safety considerations ..39 Designing for Natural and hybrid Ventilation systems .. Vent sizing .. Three major design elements of Natural Ventilation .. Types of Natural Ventilation systems .. Single-side corridor type .. Central corridor type .. Courtyard type .. Wind tower type .. Atrium and chimney type .. Hybrid (mixed-mode) Ventilation type .. Applicability of Natural Ventilation systems .. Commissioning, operation and maintenance .. Commissioning .. Operation and maintenance .. Summary ..53 References ..55 Annexes ..63 Annex A Articles included in the systematic review on the association between Ventilation and Infection .

6 65 Annex B Recommendation GRADE appraisal tables (GRADE system) ..71 Annex C Respiratory droplets ..77 Annex D Basic concept of Ventilation flow rate ..83 Annex E Rationale for determining the minimum Ventilation rate requirements ..87 Annex F Natural Ventilation example I: Hospital Nacional Dos de Mayo, Lima, Peru ..89 Annex G Natural Ventilation example II: Grantham Hospital, Hong Kong SAR, China ..95 Annex H Natural Ventilation example III: Tuberculosis Control Unit, Tan Tock Seng Hospital, Singapore ..101 Annex I Natural Ventilation example IV: IOM Isolation Centre, Damak, Nepal ..105vi Natural Ventilation for Infection Control in Health -Care SettingsTa b l e sTable Summary of advantages and disadvantages of different types of Ventilation systems for hospitals ..12 Table The scope and definitions of three transmission models for the systematic review.

7 18 Table Estimated air changes per hour and Ventilation rate for a 7 m 6 m 3 m ward ..30 Table Potential applicability of Natural Ventilation solutions in ideal conditions (consensus of a WHO systematic review) ..51 Table Decay of droplet nuclei concentration in an isolation room for different Ventilation rates and duration of time ..87 Table Infection risk with 15 minutes exposure with different Ventilation rates and quanta generation for an infector entering an enclosed space with a dimension 6 m m m ..88 Table Ward data and measured air changes per hour ..90 Table Measured Ventilation rates in tuberculosis wards ..98F i g u r e sFigure Wind-induced flow directions in a building ..27 Figure Fluctuating components contributing to single-sided airflow ..28 Figure Different Natural Ventilation and hybrid Ventilation systems.

8 34 Figure Semi-open design allowing ground-to-sky thermal radiation can greatly improve the thermal comfort in hot summer ..36 Figure The rules of thumb for the depth of the ward for three different Ventilation strategies ..44 Figure Wind-driven Natural Ventilation in the single-side corridor type hospital with wind entering the ward ..46 Figure Wind-driven Natural Ventilation in the single-side corridor type hospital with wind entering the corridor ..46 Figure Combined wind and buoyancy-driven Natural Ventilation in the courtyard type (inner corridor) hospital ..47 Figure Combined wind and buoyancy-driven Natural Ventilation in the courtyard type (outer corridor) hospital ..48 Figure Wind tower design ..48 Figure Wind-driven Natural Ventilation in the wind tower type hospital ..49 Figure Buoyancy-driven (including solar chimney) Natural Ventilation in the solar chimney type of viiContentsFigure (A) Schlieren image (visualization using light refraction caused by differences in air density) of a human cough, and (B) flash photo of a human sneeze.

9 78 Figure The Wells evaporation-falling curve of droplets ..80 Figure Patterns of air exchange during daily activities ..81 Figure Hospital Nacional Dos de Mayo ..89 Figure Floor plan and photos of different wards in Hospital Nacional Dos de Mayo ..91 Figure Improving Natural Ventilation in the outpatient waiting room of the Hospital Nacional Dos de Mayo ..93 Figure Floor plan showing the waiting hall and consulting rooms ..93 Figure Open wards and windows in the tuberculosis ward in Grantham Hospital ..95 Figure A ceiling fan for summer cooling and a radiator for winter heating ..96 Figure Ambient air temperature, wind speed and wind direction measured by the Hong Kong Observatory at Wong Chuk Hang weather station, close to the Grantham Hospital ..99 Figure Two views of the single-storey tuberculosis inpatient ward; the perimeters are free from obstruction, allowing Natural Ventilation throughout the year.

10 101 Figure Floor plan of tuberculosis unit inpatient ward ..102 Figure Inside the tuberculosis inpatient ward ..102 Figure The IOM Holding Centre in Damak ..105 Figure Individual isolation unit (left), and the gap between the vertical wall and the roof for Natural Ventilation (right)..105ixF o r e w o r dIn June 2007, the World Health Organization (WHO) released a guideline document on Infection prevention and Control entitled Infection prevention and Control of epidemic- and pandemic-prone acute respiratory diseases in Health care WHO interim guidelines (WHO, 2007). In this new guideline, Natural Ventilation is considered for the first time among the effective measures to Control infections in Health care. Such a recommendation from WHO demonstrates a growing recognition of the role of Ventilation and Natural Ventilation for Infection Control . The 2007 guideline demonstrated that further study was required in areas such as minimum requirements for Natural Ventilation and design, construction, operation and maintenance for effective Natural Ventilation systems for Infection Control .


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