WATER SYSTEM SAFETY
Left to right: Delabie’s Stop / Check connectors isolate the water supply and allow failsafe checks in front of the IPS panel; anti-scalding safety without the need for non-return valves; a TMV3-approved point- of-use shower valve with anti-scalding failsafe; Delabie’s sequential thermostatic TMT opens with cold water, and is thus ‘ideal for patient accommodation’.
The Health and Safety Executive guidelines¹ recognise
this solution, advising that TMVs should be incorporated directly into the tap. Also referred to as thermostatic mixing taps (TMTs), blending occurs at the outlet itself. A TMT with a single sequential control will not only deliver potable cold water from the distribution system when the flow is first opened, but, as the lever turns, will also provide blended water with full anti-scalding safety at full flow. Since the hot and cold water is mixed at the point of use, any potential cold water deadleg is eliminated.
The H9611P sequential thermostatic mixing valve for use in healthcare settings.
Complex mechanisms Conventional TMVs can inadvertently create conditions favourable to bacterial proliferation. The mixing chamber on most TMVs and TMTs incorporates a highly sensitive mechanism which allows it to respond to any fluctuations in pressure and temperature with a high level of accuracy and reliability. In order to function correctly, most TMVs rely on mesh strainers to prevent large particles and debris from the system from damaging the sensitive elements within the mechanism. If these are not regularly checked and cleaned, they can become clogged, and scale can build up and inevitably provide a safe haven and source of nutrients for bacteria. The thermostatic mechanism itself is also prone scale build-up, so to make sure that the anti-scalding failsafe is functioning correctly, it must be checked at least twice a year. This can be highly onerous and costly. Even with a TMT, access to shut off the water supply is often behind an IPS panel. Access can be limited and challenging, and removing the access panels can release dust and dirt into an environment where hygiene is paramount. To complicate things further, thermostatic mixers require non-return valves to prevent interconnection between the hot and cold water. Issues arise if the mixing chamber is subject to pressure changes. Without non-return valves (NRVs), if there is a sudden drop in the cold water supply – for example when several toilets are flushed, then the imbalance in the system (due to the higher pressure on the hot water side) will cause the hot water to flow back into the cold water system. This inevitably changes the conditions in the cold water supply pipe, heating the water to above 20 °C – the temperature at which Legionella is no longer dormant, which in turn risks triggering its proliferation. To prevent any cross-flow, NRVs are routinely installed
80 Health Estate Journal October 2024
on the water inlets. They only allow the incoming water to flow in one direction, operating as a check valve or backflow prevention device. Since NRVs are also very sensitive, they are also prone to being blocked by impurities. If they are not checked and serviced regularly, they can unexpectedly fail, resulting in cross-flow, and the associated challenges this entails – which adds a further responsibility for the Estates team. In real terms, what does this burden look like? HSG274
Part 2¹ states that TMVs should: ‘…be checked regularly to ensure they are failsafe if the cold water supply pressure is interrupted.’ A risk assessment should define the frequency of inspection and monitoring, which can be as frequent as quarterly, depending on the rate of fouling or other risk factors, such as patient vulnerability. So, for example, in soft water areas, an anti- scald safety test must be carried out on average twice a year. This intervention generally requires access behind the IPS panel to isolate the cold water supply. If each safety check takes five minutes, then twice-yearly checks will take 10 minutes over the course of the year. Now let’s add the filters and non-return valves.
Currently, there is no legislative or regulatory guidance on servicing regimes and maintenance programmes for NRVs. However, if we assume that checks also take place twice yearly, and that each intervention takes 10 minutes, that equates to 20 minutes per year. A 10-minute failsafe check and 20-minute strainers check equates to 30 minutes per TMV/TMT per year.
Daily cross-flow risks If we now extrapolate this to a healthcare facility with 500 beds, i.e. 500 hand washbasins each with a TMT for patient hygiene, 500 sinks with a TMT for healthcare professionals, plus 500 TMV3-approved shower mixers, this means 1,500 interventions at 30 minutes, or 750 hours per year. That equates to one engineer working a 40-hour week checking only TMVs for one third of the year. But if those checks are not undertaken, these 1,500 TMVs present 3,000 risks of cross-flow every day. Given this level of infection risk, coupled with an
onerous maintenance regime, it is hardly surprising that TMVs, and even TMTs, are no longer welcome in healthcare facilities. The risk of infection far outweighs the scalding risk. Indeed, following the deaths of six residents in a French care facility which were attributed to NRV failure, the French government took the infection risk very seriously, and updated its Medical Standard² to ban all NRVs in medical facilities. The tendency within Estates teams is therefore to replace any point-of-use TMV with a mechanical mixer, especially where the scalding risk is low. Ideal for users who are familiar with the facility and use the same basin for regular handwashing, mechanical mixers with a maximum temperature limiter offer basic anti-scalding safety. The principle is simple: limit the amount of hot water that can
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