Legionella control of blended water in healthcare premises

The management of water temperature within healthcare facilities presents a considerable challenge for Legionella control. There is an inherent tension between the need to protect vulnerable people from a dangerous bacteria (by heating water to high temperatures) and the requirement to supply water at a level which won’t pose a danger of scalding. The accepted solution to this problem is the thermostatic mixing valve (TMV), which blends hot and cold water to create a tap temperature which is suitable for safe human contact. However, from a Legionella risk perspective, TMVs create their own issues.

As the Health & Safety Executive (HSE) reminds us in its publication HSG274 Part 2, “Water systems in high risk locations (such as healthcare premises, care homes, residential homes and other situations where those exposed to the water systems are likely to be at high risk of infection) need particular consideration. The risk assessment should consider both the relative risks of Legionella and scalding.” To mitigate the risk of scalding, the use of blending values or TMVs is widespread, which in themselves increase the risk of colonisation by bacteria.

TMVs use a temperature-sensitive element and blend hot and cold water to produce water at a temperature that cannot scald (typically between 38 °C and 46 °C). Since Legionella bacteria thrives at temperatures between 20°C and 50°C, the blended water downstream of TMVs can be the perfect environment for bacteria to multiply. For this reason, the siting of TMVs is a very important consideration at the building design stage of a healthcare facility. It may be that only certain areas of the building warrant the use of TMVs, dependent on the risk of scalding. For instance, the most serious risk is where full-body immersion will take place – such as in a bath or shower – so TMVs could be used in these outlets, whereas in a hand basin the risk of serious scalding is lower.

Where it is decided that TMVs should be fitted, ideally they should be incorporated into the tap fitting itself, blending the water at the outlet point, thus minimising the storage of blended water. The type of tap is also important as low flow rate spray taps (used on hand washbasins, for instance) increase the risk due to the spray action of the water, aiding the aeration of the water particles. Where a single TMV serves multiple tap outlets the risk is also increased as the higher-risk blended water is fed through the system, potentially spreading bacteria as it flows.

If TMVs are deemed necessary, accessibility for maintenance and cleaning are also important considerations. Valves and pipework should be easy to inspect and temperature monitoring of the water must be possible.  TMVs require regular descaling and the strainers or filters associated with the valves will also need to be disinfected frequently.

Our advice would be to use TMVs wisely in healthcare facilities. They have their role to play but the increased risk they can present needs to be factored into your Legionella risk management processes, ensuring that regular maintenance is carried out and that system design is such that it limits the risk posed by the valves. Training is paramount, so that all facilities management and maintenance staff understand the risks associated with TMVs and remain vigilant to any problems.

In a healthcare setting, the vulnerability of the patients and residents is such that Legionnaires’ disease can have a devastating impact, spreading quickly and silently through the population, but with careful management and risk mitigation, a healthy and safe water supply should be a given.

Urban Environments provides Legionella control services to a number of NHS Trusts and other healthcare providers. For more information please contact us.


Article originally published https://www.linkedin.com/pulse/legionella-control-blended-water-healthcare-premises-james-homard/