The concept of safe indoor air quality for the management of indoor environment in immune buildings

Abstract

When Hong Kong picked up its economy after World War II, acceptable indoor built environment has been the challenge to many of the building services engineers. In 1990s “Healthy Building was put on the agenda in Hong Kong. Unfortunately, the outbreak of SARS and its high infectious rates in buildings shatters the arrogance of the engineers. Professor Daniel W.T. Chan hypothesized the SARS virus was propagating through the drainage systems in high rise buildings and caused the vertical cluster infection in Block E of the Amoy Garden. The hypothesis was accepted in the report by World Health Organization after the investigation panel meeting on 30th April 2003. This study identifies a bottle neck of the usual notion of “Healthy Building. The invulnerability of “healthy building lies in its incapability of protection against infection. This thesis adds an important complement for the sake of optimizing the design of acceptable indoor built environment. The classic notion of ‘healthy building’ is first enhanced by a novel concept of ‘Sustainable Immunized Building’. One of the features of this innovative approach is to provide a model for evaluation of relative protection against indoor cross infection in terms of reduction in probability through the enhancement of building and services system designs and operation. After a comprehensive review of the available models describing probability of indoor airborne infection, the Wells-Riley model, in a modified form, is used as a base. Firstly, the hypothesis of SARS virus propagation through the drainage system was demonstrated by tracer gas investigation in a 37 storey high rise residential buildings. The relative risk of cross-infection via drainage system was estimated. Secondly, a comprehensive field investigation and computational fluid dynamic analysis was conducted on the natural ventilation performance of typical high rise apartments. Thirdly, a comprehensive model is developed to explain the filtration mechanism of window type air-conditioned units typically found in residential buildings in Hong Kong. Fourthly, a new protocol is proposed for household air cleaner performance evaluation. The new “sustainable immunized building concept perfects the notion of “healthy building and provides a more valuable and pragmatic solution to protect building users.