How to prevent Legionnaires’ disease

Legionnaires’ disease is an illness caused by breathing in an infected aerosol containing Legionella bacteria. This can either be from water or soil, so buildings containing water systems (cooling towers, spa pools, hot and cold water are common sources), or garden compost and soils, are all likely sources to be aware of.

cooling towers 1

Once you have identified your potential sources then you need to carry out a risk assessment, which the UK’s Health & Safety Executive require to be “suitable and sufficient”. This risk assessment needs to identify all potential sources of risk, identify potential ways of reducing that risk (to levels deemed ALARP, see a previous post on this subject) and to provide a prioritised list of action points.

Once the risks have been identified you can then create a written scheme which identifies the maintenance tasks required to minimise the risks. This could involve removing the risk completely, for example changing a water based cooling tower to an air blast chiller or removing sinks that are no longer required, or producing a series of tasks to be carried out regularly to minimise the risks.

A list of essential tasks to carry out are described in the UK’s HSG274 which provides detailed information and guidance for cooling towers, hot and cold water systems, and other risk systems. This guidance is not an exhaustive list so you may need to look at your system and ask yourself when are the specific risks created and how can I protect humans who come into contact with the source.

hot tub

If you have a spa pool then also consider HSG282 which provides guidance specifically for spa pools.

The written scheme needs to be comprehensive and contain sufficient detail for you to manage your systems. This should include “what-if” scenarios describing how you would manage foreseeable non-conformances or events.

Don’t forget you may have a list of remedials that come out of your risk assessment so it would be useful to create an action plan checklist of these tasks to ensure you complete all of them in a timely manner. This may involve, for example, fitting point of use filters as a short term expedience whilst you resolve an issue using an engineering solution so be aware of all tasks needed to be completed.

An important part of all of this is to keep records of what has to be done and what has been done, and don’t forget to ensure all tasks are dated and signed as proof of their completion because you never know whn you might need to use these to support you if questioned about what has been done.

If you follow a logical approach to managing Legionella, supported by the available documents, then managing Legionella need not be a chore.

If you need expert help to support you in finding your way through these documents then Collaton Consultancy Limited can help you, contact us on

Find out more about Collaton Consultancy Limited at:

Further details on L8, HSG 274 and HSG 282 can be found here:


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