«Natural Ventilation for Infection Control in Health-Care Settings Edited by: James Atkinson, Yves Chartier, Carmen Lúcia Pessoa-Silva, Paul Jensen, ...»
Natural Ventilation for
Infection Control in
James Atkinson, Yves Chartier,
Carmen Lúcia Pessoa-Silva,
Paul Jensen, Yuguo Li
and Wing-Hong Seto
WHO Library Cataloguing-in-Publication Data:
Natural ventilation for infection control in health-care settings.
1. Ventilation — methods. 2. Air microbiology. 3. Infection control. 4. Health facilities — standards. 5. Guidelines. I. World Health Organization.
ISBN 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: firstname.lastname@example.org). Requests for
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The cover photographs show health-care facilities in (from top to bottom) Myanmar, South Africa, Peru, Nepal, Hong Kong SAR and Nepal.
Cover designed by Design ONE, Canberra, Australia Production and design by Biotext, Canberra Contents Foreword
Conflicts of interest
Acronyms and definitions of terms
Part 1 — Infection control and ventilation
1 General principles of infection control
1.1 The concept of isolation precaution and an historical review
1.2 Isolation practices for infection control
1.3 Isolation practices for airborne infections
1.4 Infection control for high-risk procedures
2 Concepts and types of ventilation
2.1.1 What is natural ventilation?
2.1.2 What is mechanical ventilation?
2.1.3 What is hybrid or mixed-mode ventilation?
2.2 Assessing ventilation performance
2.3 Comparison of mechanical and natural ventilation
2.3.1 Mechanical ventilation
2.3.2 Natural ventilation
2.4 Mechanical versus natural ventilation for infection control
Part 2 — Designing for natural ventilation
4 Understanding natural ventilation
4.1 The driving forces of natural ventilation
4.1.1 Wind pressure
4.1.2 Stack (or buoyancy) pressure
4.2 Ventilation flow rate
5 Design and operation
5.1 Designs for natural ventilation and hybrid ventilation systems............. 33 5.1.1 Natural ventilation systems
5.1.2 Hybrid (mixed-mode) ventilation systems
5.2 Basic design concepts for natural ventilation
5.3 Climatic and other considerations in ventilation design
5.3.1 Maintaining thermal comfort
5.3.2 Considerations for hot summers
5.3.3 Considerations for winter
5.3.4 Maintaining healthy indoor air quality
5.3.5 Managing ambient air pollution
5.3.6 External noise
5.3.7 Selecting low-emission interior materials
5.3.8 Humidity and mould growth
5.3.9 Security and vector-borne disease spread
5.3.10 High-rise considerations
5.3.11 Fire safety considerations
iv Natural Ventilation for Infection Control in Health-Care Settings
5.4 Designing for natural and hybrid ventilation systems
5.4.1 Vent sizing
5.4.2 Three major design elements of natural ventilation
5.5 Types of natural ventilation systems
5.5.1 Single-side corridor type
5.5.2 Central corridor type
5.5.3 Courtyard type
5.5.4 Wind tower type
5.5.5 Atrium and chimney type
5.5.6 Hybrid (mixed-mode) ventilation type
5.6 Applicability of natural ventilation systems
5.7 Commissioning, operation and maintenance
5.7.2 Operation and maintenance
Annex A Articles included in the systematic review on the association between ventilation and infection
Annex B Recommendation GRADE appraisal tables (GRADE system)................ 71 Annex C Respiratory droplets
Annex D Basic concept of ventilation flow rate
Annex E Rationale for determining the minimum ventilation rate requirements
Annex F Natural ventilation example I:
Hospital Nacional Dos de Mayo, Lima, Peru
Annex G Natural ventilation example II:
Grantham Hospital, Hong Kong SAR, China
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
Figures Figure 4.1 Wind-induced flow directions in a building
Figure 4.2 Fluctuating components contributing to single-sided airflow
Figure 5.1 Different natural ventilation and hybrid ventilation systems
Figure 5.2 Semi-open design allowing ground-to-sky thermal radiation can greatly improve the thermal comfort in hot summer
Figure 5.3 The rules of thumb for the depth of the ward for three different ventilation strategies
Figure 5.4 Wind-driven natural ventilation in the single-side corridor type hospital with wind entering the ward
Figure 5.5 Wind-driven natural ventilation in the single-side corridor type hospital with wind entering the corridor
Figure 5.6 Combined wind and buoyancy-driven natural ventilation in the courtyard type (inner corridor) hospital
Figure 5.7 Combined wind and buoyancy-driven natural ventilation in the courtyard type (outer corridor) hospital
Figure 5.8 Wind tower design
Figure 5.9 Wind-driven natural ventilation in the wind tower type hospital.
................. 49 Figure 5.10 Buoyancy-driven (including solar chimney) natural ventilation in the solar chimney type of hospital
vi Natural Ventilation for Infection Control in Health-Care Settings Figure C.1 (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
Figure C.2 The Wells evaporation-falling curve of droplets
Figure C.3 Patterns of air exchange during daily activities
Figure F.1 Hospital Nacional Dos de Mayo
Figure F.2 Floor plan and photos of different wards in Hospital Nacional Dos de Mayo
Figure F.3 Improving natural ventilation in the outpatient waiting room of the Hospital Nacional Dos de Mayo
Figure F.4 Floor plan showing the waiting hall and consulting rooms
Figure G.1 Open wards and windows in the tuberculosis ward in Grantham Hospital
Figure G.2 A ceiling fan for summer cooling and a radiator for winter heating............. 96 Figure G.3 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
Figure H.1 Two views of the single-storey tuberculosis inpatient ward; the perimeters are free from obstruction, allowing natural ventilation throughout the year
Figure H.2 Floor plan of tuberculosis unit inpatient ward
Figure H.3 Inside the tuberculosis inpatient ward
Figure I.1 The IOM Holding Centre in Damak
Figure I.2 Individual isolation unit (left), and the gap between the vertical wall and the roof for natural ventilation (right)
ContentsForeword In 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.
Over the past two years, a multidisciplinary team of engineers, architects, infection-control experts and microbiologists has been working to produce this WHO guideline, providing a design and operation guide for hospital planners, engineers, architects and infectioncontrol personnel. The recommendations in this WHO guideline followed a systematic review of the literature on the association of ventilation and disease transmission, as well as effective natural ventilation solutions for infection control.
This WHO guideline should be used in conjunction with other relevant infection-control guidelines.
There are very few studies on natural ventilation for infection control in hospitals. The authors of this guideline have attempted to document what is known today. Any comments from the users and readers of this guideline will be useful for future revisions and further information may be obtained at http://www.who.int/csr/natvent (and follow the ‘natvent’ links), or at http://www.who.int/csr/bioriskreduction/natvent/en/.
Dr Maria Neira Director Department for Public Health and Environment Health Security and Environment World Health Organization Dr Michael Ryan Director Department of Global Alert and Response Health Security and Environment World Health Organization
We would like to acknowledge the collaboration and generous financial support provided by the French Ministry of Health, Youth and Sport that has made the development and production of this guideline possible.
We also acknowledge the United States Agency for International Development for financial support for the development and publication of this document.
We also thank the Research Grants Council Fund for the Control of Infectious Diseases and the Hospital Authority of Hong Kong SAR for providing funding for research and field measurements for the development of this guideline.
We also thank the Asia Pacific Society of Infection Control for supporting the first multidisciplinary consensus meeting on the use of natural ventilation for infection control, 15–17 May 2007.
Finally, we thank the staff and management of the facilities used as examples in this guideline for their support and contribution.
Editors WHO James ATKINSON Yves CHARTIER Carmen Lúcia PESSOA-SILVA External Paul JENSEN, Centers for Disease Control and Prevention, Atlanta, Georgia, United States Yuguo LI, The University of Hong Kong, Hong Kong SAR Wing-Hong SETO, Queen Mary Hospital, Hong Kong SAR Authors WHO James ATKINSON Yves CHARTIER Fernando OTAIZA Carmen Lúcia PESSOA-SILVA External Pat CHING, Queen Mary Hospital, Hong Kong SAR Derek CROOME, University of Reading, United Kingdom Rod ESCOMBE, Imperial College, London, United Kingdom Yuguo LI, The University of Hong Kong, Hong Kong SAR (lead author) Li LIU, The University of Hong Kong, Hong Kong, SAR Zhiwen LUO, The University of Hong Kong, Hong Kong SAR Jianlei NIU, The Hong Kong Polytechnic University, Hong Kong SAR Marco PERINO, Politecnico di Torino, Italy Hua QIAN, Southeast University, China Matthew SALT, Salt.arq Architects, Porto, Portugal Takao SAWACHI, National Institute for Land and Infrastructure Management, Japan WH SETO, Queen Mary Hospital, Hong Kong SAR Julian Wei-Tze TANG, National University Hospital, Singapore Xiaojian XIE, Nanjing Normal University, China