Hot water storage and distribution systems pose two main risks - bacterial infection and scalding - both of which cause a significant number of injuries, illnesses and deaths each year in the UK. Managing these two risks is often considered problematic because the prevention of one directly affects the other. Jon Cockburn, head of marketing at Heatrae Sadia, discusses how to overcome the issue.
Legionella bacteria are common. They can be found naturally in water sources, meaning that they can potentially colonise in manufactured water systems. If exposed to legionella bacteria, humans can develop Legionnaire's disease, a potentially fatal respiratory condition. While the latest government figures show that the number of cases has recently fallen*, as an industry we must remain vigilant.
Legionella bacteria thrive at temperatures of between 20oC and 45oC, but die relatively quickly at temperatures above 60oC. So, in order to eliminate harmful bacteria forming in hot water storage systems, water is generally stored and distributed at 60oC or above. However, water delivered to a tap or shower at this temperature poses a serious scalding hazard, with water at 60°C being able to cause a partial thickness burn in about five seconds. Nearly 300 people a year - two thirds of which are children** - are so badly burnt by hot water that they have to be admitted to an NHS specialist burns service. Shockingly, around 20 people in the UK die as a result of scalds caused by hot bath water each year. The young and the elderly are particularly vulnerable as their skin is thinner, and they are less able to react quickly.
The most effective way to provide safe water temperatures while eliminating the risk of bacteria is to store and distribute hot water at a high temperature and use a Thermostatic Mixing Valve (TMV) to control the temperature at the point of use.
TMVs reduce the discharge temperature of stored hot water to an appropriate level by blending it with cold water before it reaches the tap, ensuring a constant and safe outlet temperature. The deadleg between the TMV and the hot water outlet should be kept to a minimal distance. This will reduce the risk of harmful bacteria being able to breed, and also helps to save water.
TMVs are approved for use by independent body BuildCert, with TMV2 valves specifically designed, built and tested for the domestic market, and TMV3 valves designed and tested specially for high risk commercial applications such as hospitals, care homes and schools.
TMVs are legally required in a number of environments, including for baths in private and housing association dwellings, housing association dwellings for the elderly, care homes for young people, schools (including nursery and those for the severely disabled), and NHS hospitals. In other environments such as private hospitals and care homes, their use is only recommended, and elsewhere, it is regarded as best practice - for instance in hotels. It's important though to remember that scalding can cause serious injuries for any adult, and that while guidance may not require TMVs by law, best practice should be followed wherever possible.
A TMV3 valve's performance is tested to comply with the NHS model engineering specification D08, meaning that it is approved for use in healthcare applications.
Approvals last for five years, at which point the manufacturer must resubmit the vales for another full test.
Even when using TMV3 valves, it's important to bear in mind that careful selection and maintenance of the hot water cylinder is equally important when guarding against legionella.
Products should be designed to meet the requirements of the Health & Safety Executive's L8 document (the approved code of practice for Legionnaire's disease). This strongly recommends that cylinders should be serviced and cleaned periodically, so integral inspection hatches are of particular benefit. A de-stratification loop to thoroughly circulate hot water is another major plus.
Cylinders like the Megaflo Commercial have been designed with these requirements in mind. An optional de-stratification loop ensures the thorough circulation of hot water, while 125mm inspection hatches improve accessibility for servicing and cleaning.
Megaflo Commercial delivers hot water at up to 90 litres per minute, and can heat up to 2,500 litres in less than 60 minutes. The range of 24 cylinders offers both indirect and direct versions, making it suitable for any commercial application. Manufactured from marine-grade stainless steel, Megaflo Commercial is extremely strong and yet lightweight, making handling and installation easier.