WATER SYSTEM HYGIENE & SAFETY
Above: Delabie’s Securitherm dual control shower mixer with no NRVs. Right: Stop / Check connectors isolate the water and verify the anti-scalding failsafe.
temperature control (1). When the left- hand control (4) is returned to the closed position, the hot water supply is closed upstream of the mixing chamber. The thermostatic cell reacts immediately, activating the anti-scalding failsafe, which shuts off the cold water supply instantly, also upstream of the mixing chamber. As a result, the water in the mixing chamber is not subject to system pressure, so there can be no cross-flow due to pressure imbalances. The only caveat is that there needs to be minimum differential between the hot water input and the mixed water output for the failsafe to operate effectively – not an issue when the hot water is distributed above 50/55 °C, and the cold water maintained below 20 °C.
Single control sequential mixers The same principle applies to Delabie’s thermostatic single control sequential basin mixers, but in reverse. The single lever controls both flow and temperature. The mixer opens with only cold water, and the hot water begins to flow once the lever has passed the perpendicular (see Figure 2), allowing the thermostatic cell to start blending the hot and cold water while taking into account pressure and temperature variations in the system. The anti-scalding failsafe technology reacts immediately if there is a cold water supply failure, shutting off the hot water
supply. Likewise, if the hot water supply fails, the cold shuts off too, meeting the TMV3 requirements for failsafe. In both instances, Delabie’s thermostatic technology for showers and mixers renders non-return valves redundant, removing a significant maintenance burden, while ensuring anti-scalding safety.
Regular maintenance, cleaning, and disinfection There are engineered solutions that can further help reduce maintenance and also promote infection control and hygiene. Stop/Check connectors allow the water supply to be isolated from the front of the IPS panels. This has two benefits: the anti-scalding failsafe can be checked by isolating the cold water at the inlet; and the mixer can be removed for cleaning, descaling, and maintenance. Where components are standardised, the mixer can be switched out to maintain continuity of use. This option is also available for deck-mounted mixers with removable bodies or spouts. Product design and material choice can
also reduce the maintenance/cleaning burden. Mixers with smooth interiors and low water volume reduce bacterial adherence. There is less standing water when the mixer is not in use, with fewer niches for bacteria to adhere. When it is in use, flow rate and turbidity are
maintained, so there is less opportunity for biofilm to develop. Moreover, switching aerators for a Hostaform spout outlet, with no internal grids or partitions, will prevent water retention and the build- up of scale. Even in the best maintained distribution
systems there is still the potential for reducing and removing unnecessary bodies of water. There is one example that is hidden in plain sight – the toilet cistern. Containing up to 9 litres of standing water, cisterns increase the contamination risk because the water is stored at ambient temperatures. In healthcare facilities the temperature is often elevated for patient comfort, resulting in ideal conditions for biofilm development. This in turn provides a safe haven for bacteria to proliferate. A study by Li, Wang, and Chen in 20204
into
virus transmission found that flushing the toilet expels these bacteria in an aerosol plume, but they can also spread back through the pipes and colonise the system. The toilet cistern is rarely considered as part of the Legionella risk assessment, but in the light of such findings, perhaps the water in the toilet cistern should be monitored?
Areas of low footfall In areas where there is low footfall, manual flushing regimes would prevent stagnation, but could be time consuming and labour-intensive. Even then, not
October 2023 Health Estate Journal 77
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