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How to reduce the risk of legionella

Legionnaires’ disease is an often underreported and severe form of pneumonia that is transmitted in buildings by pathogens in water. Here, Anthony Barnett, marketing manager at Armacell, looks at how advances in closed-cell insulation can reduce the risk of occurrence.

“The legionella bacteria enters the body by inhaling contaminated airborne water droplets from everyday activities such as showering and bathing, air-conditioning, swimming pools or whirlpools. Estimates vary between 10,000 and 20,000 cases each year.

Of particular concern is the fact that legionella bacteria multiplies where water temperatures are between 20-45°C and nutrients are available. It is dormant below 20°C and does not survive above 60°C. The bacteria multiplies rapidly in stagnant water at these temperatures and become hazardous when they are inhaled as small droplets. The risk of legionella therefore rises in summer because during the holiday period water stagnates in the pipes and the water temperatures rise.

Choice of insulation  

One of the most important preventative measures for reducing the risk of Legionnaires’ disease is to insulate both hot and cold water pipes using closed-cell insulation. That is because poorly chosen insulation can lead to the HVAC system operating in optimum conditions for the bacteria. That means hot water temperatures regularly falling below 45°C or cold water temperatures rising above 20°C.

Suitable insulation materials also prevent condensation. The best material for this is again closed-cell insulation which has a high resistance to water vapour diffusion, making it ideal for use on cold drinking water pipes. In practice, accidental damage to insulation has shown that open-cell materials, whether specified with or without a vapour barrier, do not sufficiently prevent moisture ingress as a result of diffusion. As the material becomes damp through condensation, the thermal conductivity increases and insulation properties deteriorate, causing greater energy losses. Furthermore, corrosion and other expensive consequential damage can occur as well as allowing the water temperature to enter the critical band.

Simple steps such as ensuring that cold water pipework doesn’t follow the same routes or run adjacent to space heating or hot water pipes is another way of checking the spread of the bacteria. Similar requirements apply for hot water pipes to protect them against heat loss.

When hot and cold pipes are laid in one duct or wall cavity, or wherever water is not circulated regularly, we recommend using what is known as 100% insulation. That is where the insulation thickness roughly corresponds to the pipework outer diameter. On hot water pipes this not only prevents legionella, but also protects the pipes against unnecessary energy losses. On cold water pipes the insulation provides protection against freezing in cold weather as well as providing protection against unwanted temperature rises.

The root cause of legionella is commonly down to errors made in insulation choice and installation. One of the most important preventative measures to avoid this potentially fatal disease is to insulate hot and cold water pipes with closed-cell insulation.

To find out more about Armacell high performance closed-cell insulation, visit:


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