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For the facilities manager, hot water storage and distribution systems pose two major health and safety hazards: bacterial infection and scalding. Balancing these two risks is a delicate art, because the prevention of one has a direct impact on the other. Jon Cockburn, head of marketing at Heatrae Sadia, discusses how to solve both issues.

Legionella bacteria are common. They can be found naturally in water sources, meaning that they can potentially colonise in hot water systems. If exposed to legionella bacteria, humans can develop Legionnaire’s disease, a potentially fatal respiratory condition.

Legionella bacteria thrive at temperatures of between 20o 45o

C and

C, but die relatively quickly at temperatures above 60o

C. So, in

order to eliminate harmful bacteria forming in hot water storage systems, water is generally stored and distributed at 60o

C 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 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 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, and NHS hospitals. In other environments their use is only recommended, and elsewhere, it is regarded as best practice – for instance in hotels. 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.

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.




Megaflo Commercial has 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.

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