Drainage design: Factors contributing to Sars transmission

The water-based appliance trap seal is viewed as a standard component within any building drainage system, and provides adequate protection from the miasma present within the network and sewer connection pipework. Suitable system design ensures that the pressure response of the system does not result in excursions from atmospheric that might jeopardise recommended retention levels. Underperformance, as a result of poor system design or maintenance, is typically characterised by the ingress of foul odour - an event that, although unpleasant, was not normally associated with any particular risk to health until the severe acute respiratory syndrome (Sars) outbreak in Hong Kong where 42 fatalities were attributed to transmission facilitated by the building drainage system. A method-of-characteristics-based numerical simulation model that draws upon system specification and operation to predict airflow, transient network pressures and trap seal retention levels, and facilitates an assessment of the factors that contributed to the transmission of the Sars virus, is presented. This paper thus highlights the suitability of unsteady flow simulations as a tool for the prediction of future risk.