Industrial experience and research into the causes of SARS virus transmission in a high-rise residential housing estate in Hong Kong

This report provides very practical insights as to how SARS-CoV is understood to have been transmitted among residents of a high-rise residential housing estate during the SARS outbreak in 2003.

This transmission led to a localised outbreak (or ‘hotspot’) in the Amoy Gardens housing estate, in Hong Kong. It provides an important assessment of practices employed for the design, installation, commissioning, operation and maintenance of building services systems.

Before the SARS outbreak, complaints relating to the undesired flow of foul air and sewage water from the drainage system to the residential apartments was already a common problem reported to building operation and maintenance personnel in Hong Kong. A number of explanations for this are discussed in this paper, including the issue that water traps (U-bends) in floor drains were frequently left devoid of water, thus facilitating the flow of air and potentially aerosols to apartments.

According to the SARS investigation report released by the World Health Organization (WHO), virus transmission through a contaminated drainage stack was one hypothesis for the outbreak. This study revealed that it was indeed highly possible that the building drainage system failed to perform well in confining the sewage waste within the drainage network and to allow flow only to the designated sewer.

SARS-CoV transmission through a vertical drainage stack is now believed to have been one of the routes of disease transmission. The paper includes a review of the outbreak incident; and of the observations and site measurements of foul air and water back flow in the drainage system of another vacant high-rise residential housing estate.

Tracer gas measurements confirmed an upwards flow of air in the vertical stack. These field studies allow comparisons between the gas flow from the drainage system to the living accommodation, and provide strong support for the previously hypothesised infection route.

The authors conclude that this incident demonstrates that there is still room for improvement on the safety of waste disposal in buildings. They made the following recommendations on the proper design and operation of high-rise building drainage systems:

  • Protection of water trap seal through proper trap connection and piping layout.
  • Relief of positive pressures in the vertical drainage stack due to the local surcharge condition at pipe offsets. Congested pipe ducts are usually found in buildings in Hong Kong, such that pipes and stacks are usually ‘bent’ in order to fit within the available space. These bends may actually cause blockages (if dirt accumulates). Local surcharge condition (for vertical stacks) should therefore be avoided.
  • Development of good practice on drainage piping layout design for high-rise residential buildings, to achieve maximum protection against viral transmission.
  • Development of a sizing protocol for exhaust fans in toilets and kitchens, in order to satisfy space ventilation requirements and to avoid excessive over-sizing.

The authors conclude that building services engineering professionals need to be aware of the possible causes of virus spread, in order to enhance contemporary engineering practices. They argue that a higher level of protection against disease transmission in drainage systems requires a thorough understanding of the flow characteristics of foul air and water in the building drainage network.


Hung HC, Chan DW, Law LK, Chan EH and Wong ES (2006) Industrial experience and research into the causes of SARS virus transmission in a high-rise residential housing estate in Hong Kong. Building Services Engineering Research and Technology, 27(2), 91-102.

Published by Stuart Khan

Professor of Civil & Environmental Engineering, University of New South Wales

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