Reference Project:
The SARS epidemic concentrated the attention of the drainage industry on the problems inherent due to possible cross contamination through dry appliance trap seals. No methodology existed prior to the work reported by Heriot-Watt University on the use of low amplitude air pressure transients to identify dry traps by the change in the trap characteristic reflection coefficient once water was lost. Laboratory and simulation research delivered a robust methodology believed to be adequate to identify dry traps in complex buildings. Three site tests were undertaken throughout the duration of the research programme from 2006 to 2008. The first building tested was a soon to be demolished 17-storey local authority housing block in Dundee, Scotland – Figures 1 and 2 illustrate the building and the drainage layout for one set of vertically aligned flats.
Figure 3 illustrates the successful outcome of the tests that featured at this stage a single 30 mm water gauge air
pressure pulse or transient. Depleted traps were successfully identified over the whole height of the building, as
shown in Figure 3. Figure 3. System transient response to a single positive pressure pulse incorporating directional-flow valve. Experience at the Dundee site led to the replacement of the single pulse signal with a 10 Hz sinusoidal low amplitude air pressure transient as this resulted in no discernible displacement of the traps still filled with water. This modification was fully tested at Heriot-Watt University by monitoring the trap condition within the Arrol Building, School of the Built Environment. Figure 4 illustrates the building, Figure 5 the network, and Figure 6 the accurate identification of a dry floor trap in the 5th floor boiler room. The Dundee building was soon to be demolished so there were no restraints on the testing environment or process. The Heriot-Watt University building was ‘owned’ by the research group. There was therefore a need to test the methodology in a building that was controlled outwith the research group. The RBS Facilities Management group had been a full member of the research steering panel and they offered an office building in Glasgow for the final set of tests in the EPSRC research programme. This was an operational building so that the testing had to be undertaken with no disruption to the staff – a real consideration when the methodology is eventually rolled out for general use. |
 Figure 1. 17-storey residential building in Dundee used for initial field trials. 
Figure 2. Schematic showing the standard singlestack drainage system of the 17-storey residential building in Dundee used for initial field trials. |
Figure 4 . The Heriot-Watt University, School of the Built Environment, Arrol Building used for the practical evaluation of the technique. 
Figure 6 Identification of a depleted floor trap seal, T21, in a building at Heriot-Watt University by means of a 10 Hz sinusoidal pressure wave introduced to the network. 
Figure 8. Schematic of multi-stack RBS building drainage system used for field investigations showing location of the test equipment combination and pressure transducers. |
Figure 5. Schematic of the drainage system in the
Arrol Building, Heriot-Watt University, used for
practical evaluation of the technique.
Figure 7 The RBS building in Glasgow, utilised for the evaluation of the depleted trap identification system in an operational environment and the detail of the equipment installation in an upper floor plant room. Figure 7 illustrates the RBS building in Glasgow, Figure 8 illustrates the complex multi-stack drainage network and Figure 9 demonstrates the successful application of the methodology to identify dry traps. 
Figure 9. Typical graphical output from the trap recognition programme showing test trace compared to defect free baseline and resultant absolute compliance factor. In this case for a defect at trap T4.12. The RBS tests confirmed the practicality of the developed methodology and provides the basis for the future development of the methodology in conjunction with industry.
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