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Water distribution systems

Legionella bacteria, the cause of Legionnaires’ disease, can kill. It thrives in hot and cold water distribution systems, with hundreds of cases diagnosed every year in the UK.

Traditional T-piece plumbing installations have been identified as a significant contribution factor in the promotion of legionella due to their tendency to collect and stagnate water in the “dead legs” of pipework.

Unfortunately, the industry remains largely unaware of the dead leg problem, the risks associated with it, and the alternative plumbing methods which can eliminate the threat.

In the UK more than 350 Legionella outbreaks were identified in 2010, with 10 of these cases resulting in fatalities. A typical outbreak occurred in a plumbing warehouse in Stoke-on-Trent where a hot tub was identified as being the cause of 19 illnesses and one fatality.

What’s more, the problem can’t simply be eradicated by merely flushing the system. Dead legs are often immune to flushing as the exchange of water is inhibited. Similarly, temperature control is no guarantee because the dead legs in a system allow water to cool to a temperature where the bacteria can begin to grow.

CIPHE guidelines state that the length of any dead leg should be limited to six times the pipe’s diameter, more commonly known as the six diameter rule. However, in practice, dead legs should be limited to three pipe diameters in length as five or six pipe diameters could present cleaning difficulties.

The trouble is that dead legs are too common within traditional T-piece installations in the UK plumbing industry. Even when connected to an outlet, if the outlet is not frequently used it is effectively a dead leg.

As such, the UK heating and plumbing industry needs to rethink its design and installation methods to minimise the risk to health. We need to look at alternative plumbing methods, such as loop and serial installation techniques, which are the methods used in Continental Europe.

Loop and serial installations are more hygienic than traditional T-piece systems because the risk of standing or stagnant water is minimised. Serial installations have no dead legs, fewer fittings and connections, and the total pipe length is easy to calculate.

A loop installation has the similar advantage of no dead legs, fewer connections and fewer fittings. In addition, there is no variance with the pipe dimensions and it is independent from outlet positioning.

In short, dead legs have to be designed out of any system and the traditional T-piece plumbing method used in the UK must be consigned to history. Both loop and serial installations need to be encouraged in the UK as with them we can really have an impact on minimising unnecessary legionella outbreaks and fatalities.

Mark Dowdeswell is applications manager at Uponor UK

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