In January this year, the Water Management Society (WMSoc), supported by the Health and Safety Executive and NHS Scotland, published its Guidance on the Principles of Scalding Risk Assessment in Domestic Water Systems. Scalding is a significant cause of injury in the UK, with the Chartered Institute of Plumbing and Heating Engineers (CIPHE) reporting that there have been nearly 6,000 admissions to hospitals caused by scalding injuries (https://www.ciphe.org.uk/news-and-advice/blog-articles/scalds–burns/#:~:text=Since%20I%20first%20reported%20on,pipes%2C%20radiators%20and%20heating%20appliances) since 2013/14. Effective management of scalding risk is therefore very important.
However, there is sometimes a dilemma between controlling risks from scalding and risks from bacterial pathogens, such as Legionella. To control the latter, hot water is usually heated to 60 ºC and delivered to outlets at a minimum of 50 ºC. In healthcare settings, hot water outlet temperatures of at least 55 ºC are recommended, which increases the risk of scalding in environments where people may be more vulnerable to scalding injury than elsewhere.
There are a range of approaches to reducing risks from scalding, but the most common is to fit thermostatic mixing valves (TMVs) to hot water outlets. TMVs automatically blend hot and cold water from their respective supplies to dispense water from the outlet that is at a safe and comfortable temperature for washing and bathing. However, national guidance, e.g., HTM 04-01 (https://www.england.nhs.uk/publication/safe-water-in-healthcare-premises-htm-04-01/) and HSG274 Part 2 (https://www.hse.gov.uk/pubns/books/hsg274.htm) advises against installing TMVs at all hot water outlets, recommending that they should only be installed where a risk assessment has shown that they are necessary. This is because the internal structures within TMVs are complex and provide surfaces where biofilm that could contain Legionella and other harmful bacteria can accumulate, and the blended water temperature within and downstream of the TMV can allow these bacteria to multiply. So, a comparative assessment of scalding versus infection risk is required.
Despite guidance to the contrary, it remains common practice to fit TMVs to hot water outlets in the absence of any assessment of scalding risk. This means that risks from exposure harmful bacteria might be increased unnecessarily to control scalding risks that might be insignificant. Also, at a time when resources are scarce for most organisations, the cost of maintaining TMVs, their cleaning and disinfection, and the necessary safety checks that must be carried out, can place a significant burden on already stretched budgets, often without any real reduction in risks from scalding.
The main reason for the general overuse of TMVs appears to have been a lack of guidance on what constitutes a scalding risk assessment and how to go about conducting them. The new WMSoc guidance provides practical advice on these matters, and should help ensure that scalding risks are managed effectively, without the need for unnecessary TMVs and the ongoing costs of their maintenance. By ensuring that TMVs are fitted only when a risk assessment identifies that they are necessary, risks from Legionella and other opportunistic waterborne pathogens are also likely to be reduced.
For WMSoc members, the guidance is free to download from the website (https://www.wmsoc.org.uk/knowledge/publication/220) or, for non-members, it is available as a priced publication.
