TMV Failsafe / Servicing
Temperature control is the traditional strategy for reducing the risk of Legionella in water systems, recommending hot water be stored at 60°C so that it reaches a temperature of 50°C (55°C in healthcare premises) within one minute at the outlets, however in areas of potential scalding, thermostatic mixing valves (TMV’s) could be considered.
TMV’s are valves that use a temperature sensitive element and blend hot and cold water to produce water at a temperature that safeguards against the risk of scalding, typically between 38°C and 46°C depending on outlet use. The blended water post of the TMV may provide an environment in which Legionella can multiply, thus increasing the risks of exposure.
When determining the use of TMV’s a comparative assessment of scalding risk versus the risk of infection from Legionella is required, where the conclusion of the risk assessment identifies the risk of scalding is insignificant, then the fitting of TMV’s are not required.
When the risk of scalding large parts or the whole body submersion, such with baths and showers, particularly for very young and elderly then TMV’s should be fitted at these outlets.
Where a risk assessment identifies a significant scalding risk is present, e.g. where there are very young, very elderly, infirm or significantly mentally or physically disabled people or those with sensory loss, fitting TMV’s at appropriate outlets, such as hand washbasins and sinks, is required.
HSE advises to consider the following factors:
- Where practicable, TMV’s should be incorporated directly in the tap fitting, and mixing at the point of outlet is preferable;
- Where TMV’s are fitted with low rate spray taps on hand washbasins, the risk is increased;
- TMV valves should be as close to the point of use as possible to minimise the storage of blended water;
- Where a single TMV serves multiple tap outlets, the risk can be increased;
- Where TMV’s are designed to supply both cold and blended water, an additional separate cold tap is rarely needed and may become a low use outlet.
Types of Thermostatic Mixing Valves
When conducting the risk assessment to determine whether a TMV is required, then the following information should be considered to ensure the correct valve for purpose.
- Where the scalding risk has been assessed as low (e.g. where healthy users immerse their whole body), type 2 TMVs that can be overridden by the users are required by building regulations.
- Where the scalding risk has been assessed as significant (e.g. where users are very young, very elderly, infirm, significantly mentally or physically disabled people or those with sensory loss) then type 3 TMVs that are pre-set and fail safe should be provided (but are required at healthcare premises) and should be checked regularly to ensure they are fail-safe if the cold water supply pressure is interrupted.
WES can test, failsafe, service and calibrate all types of industry approved TMVs at the agreed frequencies which can vary dependant on manufacture recommendation.
Valves that do not failsafe, or can no longer be calibrated to achieve the recommended blended temperature, then the client will be notified immediately and the valve will be either isolated, repaired or replaced.