WATER SYSTEM SAFETY
Understanding the risks While ensuring that hot water temperatures exceed the risk zone for Legionella reduces the likelihood of bacteria growth, if the design and layout of the pipework allows stagnant water to collect, there remains a risk that hot water will cool to between 25-45˚C, the temperature at which Legionella bacteria is most prolific, unless it is properly and regularly flushed from the system. Moreover, Legionella not only affects water that has been insufficiently heated or allowed to cool to within the danger zone, but can also occur where stagnant cold water within the network has been heated sufficiently to reach the 25-45˚C range due to the location of a cold water pipe or tank close to heating system pipework, for example.
It is important to note too that Legionella can affect both recent and older installations. While many of the factors affecting Legionella risk are associated with older pipework and legacy modifications to the network, water-saving initiatives designed to reduce consumption can reduce flow velocities in the pipework, and therefore impede the effectiveness of flushing regimes. Similarly, water-efficient fittings can also reduce water demand as an environmental and operational cost- saving measure. However, smaller amounts of water regularly flowing through the system could mean increased risk of stagnant water unless the pipe network has been specifically designed to adapt to these reduced flows.
Formation of biofilm
In pipework where there has been repeated or consistent stagnant water over time, a biofilm can form, increasing the risk of Legionella growth. A tacky, chemical treatment-resistant coating, biofilms are virtually impossible to remove without replacing the affected section
Individual apartments’ drinking water can be protected by using loop installations and Smatrix Aqua water monitoring equipment.
of pipe, and they increase the Legionella risk by enabling the bacteria to become embedded on the surface. Similarly, in locations where there is a high calcium content in the water supply, calcium deposits that build up on metal-surfaced pipework can provide a perfect environment for harbouring Legionella. Any areas of the system that are not in regular use are at highest risk of collecting stagnant water and creating the conditions where Legionella can breed. In a hospital environment this could include bathrooms at the end of corridors – in outpatient units or areas of the hospital that have been closed to patients for refurbishment, for example. Remodelling projects and unmapped legacy installations or modifications are also high Legionella risk areas. Alongside the dead-end sections of redundant pipe still in place despite being capped off (as referenced above), poorly designed remodelling projects can also lead to ‘dead-legs’ on the system – places on the end of the pipework network that
are seldom used, such as a bath in a bathroom where there is also a shower, sink, and toilet, for example.
Designing risk factors out The good news is that it is possible to actively design risk factors like these out of hospital plumbing installations. Improvements in pipe specification and plumbing layout can help to reduce the risk of stagnant water, biofilms, and calcification, while improving flow rates, enabling better speed of hot water delivery, and supporting increased effectiveness of flushing regimes.
Smarter specification For any hospital building services refurbishment the first consideration should be specification of the pipe to reduce the risk of Legionella growth on the network. By switching from traditional copper piping to MLC (multi-layer composite) or PE-X polyethylene pipe, the specifier can significantly reduce the risk of calcification and ensure a smoother internal surface to enable better water flow on the network. Some common joint methods on copper piping can provide small crevices that can harbour biofilms and bacterial growth, whereas MLC and PE-X pipe systems that seal on the inside bore provide a smooth marriage of the pipe and fitting, and a more hygienic connection. This simple change in specification can remove some of the conditions that support Legionella growth.
A loop installation serving all bathroom water outlets.
In addition to selecting the optimum type of pipe to protect against Legionella, it is also important to choose the right size of pipe, as this will help to determine flow rates. Correct sizing of the pipe using short pipe runs and return systems will ensure that water is flushed effectively through the system, even where water- saving measures have been designed into the installation, enabling flushing both
June 2018 Health Estate Journal 65
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