Not much of a choice, but this conflict is at the heart of every plumbing system. Water heated and stored at high enough temperatures to control and kill bacteria such as legionella can cause severe scalding injuries in a matter of seconds vs. water that is heated and stored at safe non scalding temperatures provides the ideal medium and temperatures for bacteria growth.
Legionnaires Disease
Legionnaire’s disease comes from a naturally occurring organism that can be found in low levels in the water supply. Legionnaires ‘ disease is a bacterial disease that may cause pneumonia, it is contracted from small droplets of water that are contaminated with legionella bacteria and which have become suspended in the air. The time from infection to start of the illness (the incubation period) is between two and ten days and the disease can be particularly deadly to the very young or old especially if infirm .
Aerosol droplets that allow transmission of legionella are found in - whirlpool spas, showers, cooling towers, taps with sprays etc. but Legionella can grow in any water system that is not properly maintained.
The Effect of Temperature on Legionella
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Temperature Range
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Effect On Legionella
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70-80ºC
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Disinfection range
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66ºC
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Legionella will die in 2 minutes
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60ºC
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Legionella will die in 32 minutes
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55ºC
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Legionella will die in 5-6 hours
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50-55ºC
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Legionella can survive but do not multiply
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20-50ºC
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Legionella growth range
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Below 20ºC
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Legionella can survive but are dormant
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The Burns Issue
Every year 570 people are admitted to UK hospitals suffering from severe and debilitating scald injuries. In addition 23 people are killed every year by being immersed in hot water by mistake by a carer or by falling into a bath and not being able to get out quickly enough. These are sobering statistics when you consider that the burns suffered by scald victims are every bit as painful and destructive as those suffered by victims of fires or explosions.
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| ©Reliance Water Controls Ltd |
A common scenario is a parent filling a bath to bathe a toddler in, as is common in the UK the hot tap is turned on first and then the temperature is adjusted by adding cold afterwards, suddenly the doorbell rings, the phone goes or the parent is distracted by another child and leaves the bathroom for a few seconds, the child reaches in to grab his/her favourite toy and falls headfirst into the 60ºC uncontrolled hot water. The child will obviously raise the alarm and the parent will have the child out of the water in a matter of seconds, unfortunately even then it is far too late, hot water at this temperature will result in virtually instantaneous third degree burns to all parts of the body that it comes in contact with. Almost 90% of the 570 people who suffer serious scalds each year, that require hospitalisation, are children.
Another high, at risk group are the elderly and disabled. Where children are normally scalded because they do not identify or understand the risk, the elderly and disabled are more likely to be injured or killed as a result of not being physically able to remove themselves from the scalding situation when they find themselves in danger. A typical scenario is a carer or nurse filling a bath of hot water and leaving the person to get in themselves, quite often the person will sit on the side of the bath and swing their legs over and into the water. At 60 degrees an adult will suffer 3rd degree burns after less than 6 secs. of immersion, with an elderly person this time is likely to be even less due to the more sensitive nature and thinness of their skin. Regardless of skin sensitivity though it is clear that anyone who is even marginally impeded in their movements is going to suffer a serious scald injury. 90% of all people who are killed each year by scalding are the elderly aged 65 and over.
The severity of a burn will be affected by the temperature and the time of exposure to hot water as indicated on the chart below Temperature vs. exposure time. (e = estimate)
Temp.
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45°C
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50°C
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55°C
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60°C
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65°C
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70°C
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75°C
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80°C
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Adult 3rd
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>60m (e)
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300s
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28s
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5.4s
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2.0s
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1.0s
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0.7s
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0.6s (e)
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Adult 2nd
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>60m (e)
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165s
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15s
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2.8s
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1.0s
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0.5s
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0.36s
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0.3s (e)
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Child 3rd
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50m (e)
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105s
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8s
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1.5s
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0.52s
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0.27s
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0.18s
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0.1s (e)
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Child 2nd
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30m (e)
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45s
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3.2s
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0.7s
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0.27s
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0.14s
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<0.1
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<0.1 (e)
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The table has been taken from a 1993 ASSE paper. There are a number of different published figures used to indicate the effect of temperature and time on the severity of the resultant burn. All figures used must be taken as indicators only as from the difference in published figures it is clear that the results will vary from person to person.
Legionella or Burns ? The Solution
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Heatguard® DC3 4in1
TMV3 approved thermostatic
mixing valve available
in 2in1 or 4in1,
15mm or 22mm options
|
As indicated in the time vs. temperature chart water below 50°C can be considered ‘safe’ as even for a child to receive a 2nd degree burn would taker 45 seconds, however water stored below 50°C creates a breeding ground for Legionella bacteria to breed.
The best solution to both problems is to fit a thermostatic mixing valve either at the point of use i.e. local to the taps, or as a master valve to control all of the hot water in the bathroom to a safe level. This will allow the hot water to be stored at a high enough temperature in the water heater to prevent bacteria growth but the TMV will mix cold water and hot together and discharge it out of the tap at a controlled and stable temperature typically at a maximum temperature of 48°C to prevent scalding the end user.
Buildcert and the TMV3 and TMV2 Schemes
The TMV3 scheme is the third party valve accreditation scheme which is administered by Buildcert (a division of WRc-NSF ). This scheme has been set up to independently test that valves submitted are suitable for use in high risk applications within the UK, the performance testing that is done in order to comply is based on the NHS DO8 healthcare specification but many other factors are also considered. An applying company must also prove they comply with ISO 9001 or a suitable equivalent quality control, system, the valves are checked for correct marking so they can be identified in the field, packaging and instructions are checked to make sure they comply with guidelines that are issued by Buildcert. If the TMV3 schemes technical assessment panel are convinced that all the performance and non performance related requirements have been met then they will issue a certificate granting a five year period of approval for the TMV. The valve will also be added to a list of approved products which is kept on the Buildcert website and is updated regularly. During this five year period of approval Buildcert will carry out 2 audit tests, usually after 18 months and again after 36 months, this involves Buildcert removing valves from a companies stock and subjecting them to specific tests to ensure that the production valves as well as the valves originally submitted for testing both comply with the requirements of the TMV3 scheme.
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Heatguard® DC2 TMV2 approved thermostatic mixing valve
available in 15mm or 22mm options with 4in1 accessory pack
|
In November 2003 Buildcert launched a new scheme for the testing of thermostatic mixing valves called the TMV2 scheme. The TMV2 scheme is very similar to the TMV3 but with one big difference, where the TMV3 scheme is intended to be used to certify valves for use in the high risk healthcare sector, TMV2 valves are specifically designed , built and tested for the domestic market. The basis of the performance testing for TMV2 are the European standards BSEN 1111 and BSEN 1287 all of the other requirements like audit testing, instructions, marking etc. are the same as in the TMV3 scheme.
This level of 3rd party compliance testing is unheard of in the rest of the world and helps to ensure that the UK is at the forefront of hot water safety and the development of thermostatic mixing valve technology.
For many years now Reliance has worked with regulators, charities and trade organisations to educate the public to the dangers of scalding. Reliance are 100% committed to raising the industry standards and maintaining them at a high level to ensure that thermostatic mixing valves are always fit for purpose and the public are protected from scalding injuries.
For further information on Reliance's range of Thermostatic Mixing Valves (TMVs), click HERE
or contact Reliance Water Controls on:
Freephone: 0800 389 5931
Telephone: 01386 712400
Email: sales@rwc.co.uk
Web: www.rwc.co.uk
Eric Winter, Technical Manager
March 2009
©Reliance Water Controls 2009 |
