How to minimise Legionella bacteria Cheat Sheet by Nigel Richardson

Legionella bacteria are ubiquitous and can live in water or soil. In order to cause illness they have to enter the lungs, or in rare cases enter a wound in the skin, but breathing in an infected aerosol is the main cause.

Legionella bacteria enter a building in the mains water in small numbers and then grow and increase to larger numbers within man made water systems such as showers, cooling systems, hot and cold water, and a host of other engineered systems. The system has to create an aerosol for a person to catch Legion­naires' disease from the infected aerosol.

In the water systems the Legionella bacteria find niches to live, hide and grow such as biofilms, deadlegs, in some of the materials of constr­uction and in places where they can be undist­urbed. In order to cause illness though they must also be found in the body of the water. So keeping the systems clean in the body of the water as well as system surfaces is important.

In some countries, such as the UK, there is a requir­ement to prevent people catching Legion­naires' disease in the workplace. This workplace can include factories, offices, hotels, hospitals, leisure facilities and a host of other buildings and locations. In the UK the HSE produce the documents that help companies manage safety and with regards to Legion­naires' disease this includes an Approved Code of Practice, L8, and technical guidance, HSG 274, which comes in three parts.

The Respon­­sible Person is the key person in managing Legionella as it is that person who should ensure the policies and processes for minimising Legionella are in place and are carried out.

Once the risk assessment is in place this will identify the risks on site which will lead to a series of works to be carried out. These works are split into on-going and remedial tasks. Knowing what the risks are and what works are required to be carried out leads to the creation of the control scheme. This control scheme is known as the "­Written Scheme­" or it can be called the "­Water Safety Plan"

Other countries may have their own guidance and the World Health Organi­sation also has a detailed document describing the schemes for contro­lling Legion­ella.

This written scheme is therefore an important document that an organi­sation needs to create, whether it be a paper based or electronic system, that fully describes the policies, systems and operations carried out on site to minimise Legionella bacteria.

Key to successful management of Legionella bacteria is the training and competence of all staff involved in the process. Relevant training and competence is required based on the role fulfilled. For example toolbox talks may be sufficient if a person is just carrying out temper­ature checks but this is not sufficient for the Respon­sible Person who will require more detailed, indepth training.

The Respon­sible Person should also ensure chosen contra­ctors are competent and suitably trained for the tasks they are carrying out. For example water treatment companies should ensure their staff are suitably trained and experi­enced for the tasks they carry out on site. Contra­ctors who carry out plumbing tasks on site should also understand the effect of their work on Legionella manage­ment.

The risk assessment carried out will identify the risks on site and using this knowledge the control scheme is created. The control scheme will show the on-going tasks that are required to be carried out. In the UK the details of what is required can be found in HSG 274.

On-going monitoring is a vital part of minimising Legionella as by carrying out various tests and activities you can determine whether the systems you are managing are under control or likely to be allowing Legionella to prolif­erate.

A well designed and managed set of on-going monitoring tasks is key to managing Legionella and reducing the risks that somebody may contract Legion­naires' disease.

Legionella likes to live in biofilms, scale and sludges on surfaces as it is an ideal enviro­nment for the bacteria to seek protection and food. Conseq­uently a system that has these deposits can encourage Legionella bacteria to prolif­erate.

Biocides can be used in all systems to minimise biofilms and so reduce Legion­ella's ability to survive inside a biofilm.

Temper­ature is a key tool in managing Legionella bacteria in hot and cold water systems. Legionella bacteria thrive in temper­atures between 20^oC and 45^oC and so avoidance of these temper­atures is important.

Note that 50^oC is hot enough to scald some people and so in some circum­stances a Thermo­static Mixing Valve or Thermo­static Mixing Tap is used to reduce the hot water to a safer temper­ature. If these are present then extra works will be required as part of the on-going monitoring to ensure they are kept clean and free from bacteria.

Ways should therefore be found on site to ensure hot water is kept hot and cold water is kept cold to reduce risks.

In some systems, such as cooling systems, spa pools and process waters, it is permis­sible to use industrial biocides to kill or control bacteria, including Legion­ella. In hot and cold water, which is fit for human consum­ption, the choices of allowable biocides is much more restri­cted.

The biocides most readily approved for use are chlorine and chlorine dioxide, which are known as "­oxi­dising bioxid­es" though there are other oxidising biocides which may be used. There are also "­non­-ox­idi­sin­g" biocides that can be used in some circum­sta­nces.

It is unlikely that a Respon­sible Person has all of the skills and compet­ences required to manage a site by themselves and so contra­ctors are often used to help.

Contra­ctors should be able to show experi­ence, skill and competence relating to the task required of them. In the case of water treatment companies this means their staff should know how to carry out suitable and sufficient risk assess­ments, manage water systems, advise on the use of chemicals and how to compet­ently clean water systems.

Bearing in mind the seriou­sness of Legion­naires' disease it is worth taking time to choose the contractor you trust and will be happy working with to manage Legionella on site.

You now have a suitable and sufficient risk assessment identi­fying the risks on your site, from this you have identified the remedial tasks required to bring your systems up to a suitable standard, and have a list of on-going monitoring tasks.

Systems will change over time, bacteria, being living organisms, will grow some times faster than others, standards and rules will change from time to time.

Whatever means you choose you should learn from the inform­ation you have as this means you can reduce the risks on site. Look at trends and at how you remediated problems as these same issues may well reoccur.

All of this inform­ation, your systems, processes and learning will prove to someone like the HSE that you have Legionella under control. It may not be possible to eradicate Legionella but what is possible is to have a well managed system in place to control Legion­ella.

If after reading this you find that you need external help and support then take a look at the following websites: