WATER SYSTEM SAFETY
Do TMVs still have a viable role in healthcare?
Historically, thermostatic mixing valves (TMVs) have played a vital role in protecting vulnerable users. However, recent scrutiny has cast doubt on their efficacy, prompting some facilities to explore alternative solutions, says Carole Armstrong, Senior Marketing manager at Delabie, who here asks whether thermostatic mixing valve technology still has a role to play in modern healthcare settings.
In healthcare environments, the balance between anti- scalding safety and the risk of Legionella infection is a perennial issue. Temperature control regimes have always been crucial for managing the risk of waterborne infection while mitigating the risk of scalding. Thermostatic mixing valves (that comply with NHS D08 performance specifications, i.e. are TMV3-approved) have typically played a significant role in protecting vulnerable users, but in recent years their reputation has become somewhat tarnished. Alternative mechanical solutions have been implemented to address the concerns raised by estates teams. So, will the thermostatic mixing valve (TMV) be consigned to the great scrap metal recycling heap, or does it still have a role to play in today’s healthcare environments? Legionella control regimes in healthcare domestic hot water distribution systems mean that hot water at 55 °C is circulated right up to the point of use to prevent bacterial proliferation. However, this elevates the risk of scalding at the point of use. The Health & Safety Executive’s Technical Guidance for Legionnaire’s disease (HSG274 Part 2)¹ states that TMVs should be used where there is a high scalding risk, such as where there is full body immersion for baths and showers, and for hand washbasins and sinks where the risk is highest – i.e. for people who are infirm, elderly, very young, or significantly mentally or physically disabled, and also those with sensory loss.
Technology non-grata TMVs provide optimal anti-scalding safety. A temperature- sensitive cell adjusts the incoming hot and cold water flow so that the mixed water output is controlled to a very high degree of sensitivity. Variations in the incoming water temperature and pressure are compensated for
immediately, ensuring that the mixed water is delivered at a safe, constant temperature to the user. The thermostatic cell reacts instantly if there is a cold water supply failure, shutting off the hot water supply. Likewise, if the hot water supply fails, the cold supply shuts off too, meeting the TMV3 requirements for anti-scalding safety, i.e. failsafe. So, if user safety and comfort are preserved, and the risk of Legionella is mitigated, why have TMVs become technology non-grata? For users most at risk from scalding, the potential for infection by Legionella bacteria is also high, and the solutions to overcome both risks involves an advanced technical solution. However, these engineered solutions have led to a rise in concerns about the role of TMVs in contributing to contamination episodes. These concerns centre on the possibility of a cold water deadleg downstream of the TMV, the complexity of the thermostatic mechanism as a factor in bacterial development, and the associated filters and non-return valves as potential contamination sources.
Cold water deadlegs Location is everything when it comes to TMVs. A group TMV serving a run of showers and/or washbasins will inevitably result in a cold water deadleg downstream of the TMV, since mixed water is already blended to a safer, more comfortable temperature. The cold water draw-off is therefore infrequent, allowing biofilm time to establish significantly, and increasing the risk of bacterial contamination in the cold water pipework. In recent years there has been a determined switch to point-of-use thermostatic technology with TMV3 approved anti-scalding failsafe, which can operate with flow rates as low as 3 litres per minute.
Below left: Delabie says its sequential thermostatic mixer provides anti- scalding safety for vulnerable users.
Below right: ‘Next- generation’ thermostatic mixing valves need no non-return valves.
October 2024 Health Estate Journal 79
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