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Legionella bacteria can breed in any water system and can cause a wide range of diseases. When designing and installing a safe hot water system, it is vital to mitigate against the risk of a spread of pathogenic bacteria – particularly in healthcare premises or education facilities – using appropriate protective equipment as recommended by the Department of Health1


, often


including the use of a flow­through expansion vessel. Amy Sedgwick, assistant commercial product manager, ACV UK elaborates


egionella can thrive whether water is stagnant or flowing and – given the right temperature and conditions – can multiply rapidly2


. All of the


diseases caused by legionella can be very dangerous for the clinically vulnerable or elderly and, therefore, guarding against the risk of spreading the bacteria in healthcare and care facilities is an imperative.


Legionellosis diseases are rare but previous studies showed a rise in infections in the UK, with PHE reporting3


over 500 cases in England and


Wales in 2019. The picture improved for 2020 with only 295 cases, however this could be due to the pandemic as cases from travel were much lower than the previous years because the country was in lockdown for a large part of the year. The key is understanding prevention and designing any hot or cold water system to prevent the formation and growth of Legionella and other bacteria.


Legionella and the law In 2018 a hospital was fined £300,0004


BOILERS & HOT WATER


Using flow­through type expansion vessels to reduce risk of legionella


When an unvented hot water system is running as usual, an expansion vessel will routinely partially empty and fill, exchanging water from and to the wider system at regular intervals.


However, expansion vessels have been identified by the HSE as specific points at risk of Legionella as they can suffer from low flow rates or stagnant water – particularly if the system pressure and temperature remain steady over a period of time. This is especially true of large commercial properties such as university buildings as well as public buildings such as hospitals and healthcare facilities. In the current climate this is particularly prevalent, as many schools, office buildings and entertainment venues have been closed or operating at a far lower capacity and therefore running the risk of reduced flow in their water systems.


and a


private care home £3 million for breaches of health and safety regulations after deaths resulting from Legionnaires’ disease. When installing and managing water systems all duty holders must adhere to the practical guidance from the Health and Safety Executive’s (2013) Approved Code of Practice ‘Legionnaires’ disease: The control of Legionella bacteria in water systems (L8)’5


.


Across the Healthcare sector there are two key pieces of legislation; The Health and Social Care Act 2008 (Regulated Activities) Regulations 2014, specifically Regulation 12(2)(h) and Regulation 15 of the Act.


Best practice guidance underpinning these laws are laid out in the Health Technical Memorandum 04-01 – ‘Safe water in healthcare premises’6


.


Although aimed at healthcare, we are seeing this document used farther afield including at Universities and Schools.


Unvented systems and the risk of legionella


The primary method of risk reduction is to control the system temperature, but, this is not always enough to control bacteria within the system. Insufficient flow along with the right temperature range (20-45°C) could promote legionella bacteria in any system.


Expansion vessels in any hot water system run the risk of introducing microbial colonisation (including legionella) to a system as ‘plantroom temperatures usually exceed that of the incoming water’ (Health Technical Memoranda 04-01 (HTM)), and in a pressurised system there may be long periods where there is no water flowing through the vessel causing the residue water to become stagnant. The HTM 04-01 states7


that ‘vessels with a ‘flow-


through’ design should provide less opportunity for water to stagnate and become contaminated’.


The benefits of a flow­through type expansion vessel


Unlike standard expansion vessels, flow through type expansion vessels include a Flowjet valve (sometimes referred to as an ‘anti-legionella valve’) to ensure continuous flow of water through the bladder. Regardless of the change in water pressure, this valve diverts part of the water flow into the vessel to continually renew water within the vessel, preventing water stagnation and therefore guarding against legionella formation. These valves also allow for vessels to be drained, bypassed or isolated in the case of removal or replacement. The flowjet valve supplied with specifically designed flow-through expansion vessels - and the T piece supplied with the larger of these vessels – also removes the need for pipework from the top of the vessel as they facilitate the same movement of water, but within a standard pipework system design.


Conclusion


With legionella bacteria posing such a significant risk to life - if allowed to spread through the water systems - and with Legionnaires’ disease having such a high mortality rate the potential fines and legal impacts to property owners following an outbreak are appropriately significant as a result. It is therefore incumbent on the system designers and property managers of all establishments to ensure that water management systems are designed and implemented in such a way as to minimise that risk.


ACV Smart Cylinder with standard expansion vessel


1 Health Technical Memorandum 04-01: Safe water in healthcare premises. Part A: “Design, installation and commissioning.”


2 Legionnaires’ disease, the control of Legionella bacteria in water systems, Approved Code of Practice and guidance on regulations, Health & Safety Executive, L8 (Fourth edition), 2013, p.6


3 https://www.gov.uk/government/publications/legionnaires-disease-monthly-surveillance-reports-2019 4 https://www.bbc.co.uk/news/uk-england-bristol-43842469 5 https://www.hse.gov.uk/pubns/books/l8.htm


6 https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/ file/524880/DH_HTM_0401_PART_A_acc.pdf


A schematic showing two ACV water heaters and expansion vessels 16 BUILDING SERVICES & ENVIRONMENTAL ENGINEER FEBRUARY 2022


7 Health Technical Memorandum 04-01: Safe water in healthcare premises Part A: Design, installation and commissioning https://www.gov.uk/government/collections/health-technical-memorandum- disinfection-and-sterilization


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The Flowjet valve ensures continuous flow of water through the bladder of the expansion vessel


As a key part of any water system design, you must ensure that the expansion vessel - used to efficiently manage the change in pressure in a closed system - is the optimal selection to keep the risk of legionella bacteria to an absolute minimum.


Thanks to continuous developments in product design, equipment such as flow-through type expansion vessels – with specifically designed flowjet valves to maintain constant water flow – are now more readily available. This makes it far easier to make appropriate selections and uphold your duty of care in ensuring premises are safe for patients, residents, students, and staff.


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