Transient defect identification in building drainage and vent systems – an application of pressure transient theory and practice

Defective trap seals have been conclusively shown to be a public health hazard in complex building drainage and vent systems. Dry traps, either as a result of poor design, maintenance or system operation provide a cross contamination route for the ingress of infection into habitable space. The practicalities of system maintenance prevent the regular and routine checking of all system traps to prevent dry or semi-depleted traps remaining unidentified. A remote non-invasive technique to provide facilities management operatives with an indication of the areas most at risk and system designers with guidance as to the possible need for system modifications would ensure system compliance with performance standards.Low amplitude air pressure transients are propagated within building drainage and vent systems in response to appliance discharge. Such transients are reflected and transmitted by each boundary encountered, whether branch to stack junctions or terminations formed by traps or any control device. This normal transient propagation may be employed to indicate depleted trap seals due to the dependence of the termination reflection coefficient on trap condition.This paper will confirm the theoretical basis for a non-invasive monitoring system and will present laboratory and site test results confirming the application of the pressure transient theory. The paper will also identify the limits of the solution in terms of transient magnitude and the considerations necessary to determine the number and location of transient generators required for any complex network and the underlying theory determining suitable monitoring locations.