Controlling legionella with elevated water temperatures
Within hospitals, healthcare, social care and similar settings the primary means of controlling the growth and proliferation of Legionella bacteria in hot water systems is by thermal control, which involves using elevated water temperatures. Current guidance set by the Department of Health in their “Health technical memorandum HTM 04-01: Safe water in healthcare premises” states that hot water should be stored at a minimum of 60°C and dispensed at a minimum of 55°C.
If hot water used for showering or bathing is above 44 °C then there is a significant risk of serious injury or even fatality, especially where large areas of the body are exposed to high temperatures. Such elevated water temperatures therefore need to be carefully controlled and managed, especially where those at higher risk of scalding injury are exposed.
What is a thermostatic mixing valve (TMV)?
A thermostatic mixing valve (TMV) is a specially designed plumbing valve that carefully mixes hot and cold water to control hot water outlet temperatures to safe levels. TMVs are used in health and social care environments to protect people by reducing the risk of scalding from very hot water from showers, baths and wash hand basins.
How does a TMV work?
TMVs are precision mechanical valves that are designed to regulate and maintain water temperatures to safe levels even when water pressures or flow rates fluctuate.
How do they work? As hot and cold water enters the mixing valve it is carefully blended using an internal thermal element to output a mixed water stream at a pre-set temperature that is typically between 39°C and 43°C. This is the recommended temperature range for hot water outlets where a TMV is installed.
TMVs also incorporate an essential failsafe mechanism that will automatically shut down the valve if either the cold water or hot water supplies fail. This ensures that people are protected from dangerously high hot water temperatures (interrupted cold water supply), and thermal shock from cold water (interrupted hot water supply).
Why are TMVs important for safety?
Children and the elderly are particularly at risk from scalding from hot water with accident statistics showing that nearly 600 people suffered serious scald injuries in the UK each year. 75% of the victims of severe scalds were children under five years of age. Additionally, the figures also show that older people are at particular risk with those over the age of 65 accounting for almost two thirds of all fatalities in the UK.
RoSPA have campaigned long and hard for the introduction of TMVs in the wider community. Tom Mullarkey, RoSPA chief executive said:
“Young children and older people are most at risk from bath water scalds because their skin is thinner and therefore less able to withstand higher water temperatures than other age groups. Because of this, they can suffer a scald more quickly, at lower water temperatures, and often the burn is much deeper”.
Additionally, people with a reduced capacity, mobility or temperature sensitivity, together with those who cannot react appropriately, or quickly enough to prevent injury are also at greater risk. The installation and regular maintenance of TMVs helps to protect such vulnerable groups from scalding.
What are the regulatory requirements in hospitals, health & social care settings?
All hospitals, healthcare, social care and similar properties that fall under the Care Standards Act 2000 should be fitted with thermostatic mixing valves that meet the NHS Model Engineering Specification D08 and NHS Estates – TMV manufacturers TMV3 performance standards of thermostatic protection.
TMV3 valves are designed, manufactured and tested to offer improved thermal performance including a faster failsafe function and improved control when the TMV3 is subject to variable water flow and temperature fluctuations.
TMV3 valves are designed, manufactured and tested to comply with the NHS Model Engineering Specification D08 standards.
TMV2 valves offer a lower standard of thermal performance to TMV3’s and are suitable for use in most domestic properties and under certain circumstances, sheltered housing accommodation.
How often should TMV3 valves be tested & serviced?
In health and social care settings TMV3 valves must undergo regular in-service tests to ensure they perform correctly. If a valve fails an in-service test, the valve must either be serviced in accordance with the manufacturer’s instructions, or if can not be serviced it should be replaced. If the manufacturers instructions are unavailable then servicing should follow the guidance given in the NHS Model Engineering Specification D08 which states that the first in-service TMV test must take place between 6 and 8 weeks after commissioning, with a further after 12 to 15 weeks.
Regular on-going in-service tests should be carried out to demonstrate adequate thermal performance is being maintained at the TMV3.
In-service TMV testing
Regular in-service testing of TMVs is essential to ensure they operate correctly, delivering safe water temperatures between 39°C and 43°C. This is the recommended temperature range for hot water outlets where a TMV is installed.
All TMVs should be tested and the results compared to those recorded during the original commissioning stage. Where there is no significant change to the outlet temperature (≤ 2°C) and the failsafe shut-off activates as it should, the TMV is considered to be operating correctly. However, if the water temperature has increased by more than 2°C or the failsafe does not work, a full TMV service plus recommissioning, or valve replacement will be required.
TMV servicing & maintenance… What does it involve?
Our in-service TMV servicing and maintenance solutions are delivered by experienced, in-field water treatment and engineering experts and include the following:
