Automatic detection of depleted fixture trap seals using the reflected wave technique

The loss of fixture trap seals presents a potential cross-contamination
route for sewer borne pathogens. The defective trap identification method
was developed to assess the status of trap seals using a non-destructive
“sonar-like” test based on the reflected wave technique. System diagnosis,
proven over several years of laboratory and sited-based validation,
primarily depended on manual interpretation of system pressure responses
to identify the trap location from the reflected wave return time. This paper
advances the technique by introducing the developed “TRACER” program
which includes a time series change detection algorithm allowing automatic
system diagnosis. Outputs were validated against simulations using the
AIRNET numerical model which, together with the “PROBE” Method, was
used to determine trap pipe periods, and therefore the location of defective
trap seals, with improved accuracy over those calculated theoretically. This
technique thus provides a reliable and automated approach to monitoring
the protective seal between habitable space and the sewer network.