It has happened to all of us, you turn on the hot water tap just to get a scalding flow of very hot water from the tap. The pain and sensitive skin that follows is the lowest level of injuries that are caused every year in the UK from overheated water, which in extreme cases leads to fatal injuries.

In autumn 2007 the Health and Safety Executive has introduced new directives for care homes. According to the new directive they have to install thermostatic mixing valves and make them temper proof. This latest development follows a tragic case of a fatal injury from scalding water.

The Building Standard in Scotland currently includes a requirement to install thermostatic mixing valves in all new housing developments or major re-developments. It is not yet compulsory in England and Wales, but there is indication the Building Regulations authorities are reviewing this issue.

When storing hot water inside a domestic hot water cylinder, the requirement is to keep the water at a temperature of between 60c to 65c. At this level it is believed that Legionella virus does not survive. It is, however, important to note that at such a high temperature the hot water must be mixed before exiting the taps to reduce the risk of scalding.

TMVs are particularly important in public buildings or properties with communal water heating systems. Hot water regulations in the UK require water to be kept at high temperature throughout the system (up to the point of delivery) to reduce the risk of Legionalla.

Young children and old people are the most at risk from scalding water injuries. Hundreds of young children are admitted every year to hospitals in the UK with severe burns from hot baths. Their extra sensitive skin gets burned easily and they may be left with permanent scars. Similarly, older people may not feel the heat of the water fast enough or react fast enough to turn off the hot water tap, leading to severe burns. The same is true for mentally or physically impaired people that have slow response time and slow reactions to pain.

There are primarily two types of thermostatic mixing valves that are certified and approved for installation:

TMV2 valves are primarily for domestic installations, but they are appropriate for most other premises. In any such installation a risk assessment must be done to review whether disabled or mentally challenged people use this property.

TMV3 kits are required in healthcare premises and properties for disabled or handicapped people. TMV3 systems are designed with tighter tolerance levels, thus ensuring better safety levels and more accurate mixing performance, better protecting the users.

Manufacturers of thermostatic mixing valves recommend that they are installed only by qualified plumbers. The valves are positioned between the hot and the cold pipes to prevent the water coming out of the tap at an extremely high temperature. Most common TMVs are installed under the bath or under the hand basin for a simple installation. Most kits are sold with tailpieces which include isolation, a strainer and test points. Some kits have flexible connectors and isolating filter vales to deal with space limitations.