How to Kill Legionella - Part 2: The War
I'm not a military man, but I'm certain there's a lot of planning involved in winning a war. I also assume that a highly effective way of chasing an enemy off your territory would be to make the environment they occupy uninhabitable.
In this context, your enemy is Legionella, a relentless threat to your water safety and business reputation. It's persistently supplied to you, at very low levels, through your incoming town mains.
The environment they seek to inhabit are your water systems. It really isn't fussy about which one.
• Cold Water Systems Operating Too High: This is fundamentally a result of warmer ambient temperatures being given sufficient time for a transfer of heat between the colder pipes. The reasons why that sufficient time is created are varied, but it's always linked to an insufficient demand for water to maintain a high enough turnover that would naturally prevent it.
• Hot Water Systems: These are often significantly more complex in design and, as a consequence, more susceptible to Legionella colonisation when not suitably managed.
To conserve water and the energy it takes to heat it, larger systems will operate using a flow and return pipe arrangement, creating a moving circuit of water driven by a pump. These circuits can become very complex in large buildings, with subordinate loops created to supply smaller areas.
There are too many reasons to explain why a hot water system that may have been correctly balanced at some point in time stops circulating correctly. However, the consequence of this happening is far simpler. No circulation anywhere in a system will result in water stagnation, at a temperature ideal for bacteria development.
Further to this, and a fly in the ointment when undertaking disinfection works, any water contained within a dormant return pipe will be mechanically trapped there. The cause of the imbalance that has developed could be a wide range of things, but the water will only ever be moved by the circulation pump, and any disinfection procedure will fail to penetrate a colony of Legionella that has made its home in a 'short-circuited' return leg.
Reflect on Your Battle Plan
Now is the time to reflect on your current Legionella battle plan and perhaps consider what you know about the environment in which you welcome all the Legionella you are gifted each day by your Local Water Authority.
It is likely that the entire assessment of whether your hot and cold systems are suitably operating at temperatures that prevent Legionella growth (<20°C or >50°C) is based on some information collected once a month by someone at some point during a calendar month.
A Better Way to Control Legionella
There has always been a better way to control Legionella; the ability to monitor temperature with sensors has been around for decades. It's only now, with the growth of the Internet of Things (IoT), and the ability to access, view and share data, that the ineffectiveness and futility of traditional Legionella control methods has been fully exposed.
See Part 3 of the blog – The War Cry – to see how victory can be yours!
For further information, please refer to the following HSE guidance:
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