BEAMAEnergy director Dr Howard Porter, who heads up the Thermostatic Mixing Valve Manufacturers’ Association (TMVA) discusses the benefits of TMVs in the context of the Scottish Building standards agency’s recent announcement regarding new regulations for maximum temperatures of hot water for bathing.
In response to a public petition, allowed under the Scottish legislative, the Scottish buildings standards minister has announced (2 February 2006) that in all new and refurbished buildings the maximum temperature of delivered hot water must not be higher than 48oC for bathing use.
With the legislation coming into force during May 2006, this has implications for installers and building designers.
The Scottish legislation in full
The legislation in Scotland is presented in a series of technical handbooks downloadable from www.sbsa.gov.uk
Below is the relevant information for domestic installations. Similar information for the non-domestic sector is also on the sbsa site.
Guidance to the Water Byelaws recommends that to prevent the development of Legionella or similar pathogens, hot water within a storage vessel should be stored at a temperature of not less than 60º C, and distributed at a temperature of not less than 55º C.
If water is supplied at high temperature, from any source, there is a danger of scalding to building users. Risk of severe injury increases proportionally with increase in temperature and with extent of contact.
It says that to prevent scalding, the temperature of hot water, at point of delivery to a bath or bidet, should not exceed 48º C.
A device or system limiting water temperature should not compromise the principal means of providing protection from the risk of Legionella. It should allow flexibility in setting of a delivery temperature, up to a maximum of 48º C, in a form that is not easily altered by building users.
This will allow reduction of temperature where, for example, facilities are used by those more at risk from injury, such as elderly people or unsupervised children.
Where both hot and cold water are supplied to a facility, the above may be achieved by use of a thermostatic mixing valve (TMV) or fitting complying with BS EN 1111 or BS EN 1287, fitted as close to the point of delivery as practicable.
Guidance on the installation, use and maintenance of thermostatic mixing valves and fittings can be found in BRE information Paper IP 14/03 and from the Thermostatic Mixing Valve Manufacturers’ Association (TMVA) web site: www.tmva.org.uk.
Where a dwelling is altered or extended, but not converted, and new sanitary facilities are provided, some primary heat sources such as older combination boilers, may not be suited to temperature control as described above.
In such cases, advice should be sought from equipment manufacturers on compatible means of limiting hot water temperature to controlled facilities.
Dangers of hot water
Water need not be boiling to scald. Temperatures above 45°C can cause serious injury. For example, at 60°C partial thickness burns can occur in approximately seven seconds, and full thickness burns in 90 seconds.
At 70°C, these times shorten to less than one second and 10 seconds respectively. For most domestic installations the maximum temperature agreed for Scotland of 48oC is appropriate allowing non-vulnerable users to bath at high temperature, whilst protecting all users from excessive temperatures.
In healthcare, scalding is the largest single cause of fatal accidents to non-employees. The elderly, the very young and the physically or mentally impaired are especially vulnerable while using baths, showers and sanitary facilities. Yet, all scalding accidents are wholly avoidable.
In many other building types, scalding can cause significant injury. There have been many court cases - and prosecutions - for building owners who have not carried out the appropriate duty of care requirements.
How thermostatic mixing valves work
Hot water needs to be stored at temperatures typically above 65°C to avoid bacteriological contamination (particularly Legionella).
But, it needs to be delivered at or below 40°- 45°C to prevent injuries from scalding at the tap or shower. TMVs can satisfy both these requirements.
Fitted in the hot supply to terminal fittings, TMVs blend hot and cold water and ensure a constant and safe outlet temperature, eliminating any risk of scalding. They instantly shut off the flow of water in the event of an interruption to either hot or cold supply.
There are two approval schemes for TMVs that ensure all products tested and qualifying for approval can be trusted to deliver the performance required in specific installations situations.
Both schemes are administered by BuildCert. The TMV3 scheme covers valves for healthcare and other situations where venerable persons are at risk. TMV2 is for lower risk situations, mainly domestic installations.
Mandatory in healthcare
In NHS premises, TMVs are mandatory in risk situations under the provisions of the Health Guidance Note (HGN) entitled ‘Safe Hot Water and Surface Temperatures’. Class 3 risk situations require TMVs complying with NHS Estates Standard DO8, which are third party approved by TMV Scheme 3, and listed as DO8 compliant for the application.
Essential precautions against scalding during bathing/showering include the use of Engineering Controls (ie TMVs), staff training, supervision, plus risk assessment of the vulnerability of all those with access to bathing facilities.
Harsh penalties await any organisation with an established duty of care that neglects these precautions.
Installers working in this sector need to be aware of the dangers of scalding, and of how to properly apply and install TMVs to provide safe hot water supplies.
Future regulatory changes
The changes announced in Scotland will have a major impact on the use of TMVs UK-wide - not just north of the border. It is thought that a number of builders will be specifying TMVs in all new build as a result of the legislation.
Additionally, it is hoped that the Scottish decision will persuade ministers in London to legislate in a similar way south of the border. It is hoped that over the next few years a combination of regulations and market dynamics will extend the opportunities for safe bathing to all households.