Legionella Risk Assessment – information sheet


Legionella bacteria are ubiquitous in nature and commonly colonise air conditioning plant, water storage tanks, hot and cold water distribution systems and spa baths. Where conditions are right the bacteria can multiply to significant numbers and present a risk. Infection is caused by the inhalation of Legionella bacteria in the form of an aerosol. To cause infection the bacteria therefore needs to become airborne for example from a shower, spray tap or cooling tower.

Legionellosis is a generic term given to respiratory infections, such as Legionnaire’s disease, caused by Legionella bacteria. Over fifty different species of Legionella have been identified. Only a few species have been directly associated with outbreaks of infection. Legionella pneumophila Serogroup 1 is the most commonly identified form of the bacteria and is responsible for over 80% of the fatalities arising from Legionnaire’s disease. On average there are around 300 – 350 reported cases of Legionnaires’ disease in the United Kingdom per annum.

Guidance and Legislation

The requirement to consider, prevent and control the risk from Legionella bacteria which may arise from work activities is covered as part of the duties under the Health and Safety at Work Act 1974. Within the framework of health and safety legislation other regulations are relevant, particularly the Control of Substances Hazardous to Health Regulations 2002 and the Management of Health and Safety at Work Regulations 1999.

In support of the legislative documents the Health and Safety Executive in the UK has published an Approved Code of Practice. ‘Legionnaires Disease, The control of legionella bacteria in water systems’ (ACoP, L8 4th ed.) sets out requirements and guidance on the measures to be taken to prevent or control the risk from Legionella bacteria.

The ACoP, L8, Paragraph 2 states that, to comply with their legal duties, duty holders should:

  • identify and assess sources of risk;
  • prepare a scheme for preventing or controlling the risk;
  • implement, manage and monitor precautions;
  • keep records of the precautions and ensure that records are maintained and available for at least five years;
  • appoint a competent person to help take the measures needed to comply with the law

This report comprises a risk assessment for the identification and control of the risk from Legionella bacteria in water systems. It provides details of the water systems listed in the asset register, identifies areas of risk and sets out the recommended control actions to form the basis for the written scheme for preventing or controlling the risk where applicable.

Risk Assessment

The ACoP, L8, Paragraph 28, sets out that:

‘a suitable and sufficient assessment must be carried out to identify and assess the risk of exposure to Legionella bacteria from work activities and water systems on the premises and any necessary precautionary measures needed’

The purpose of the assessment is to enable valid decisions to be made about the level of risk to health and the necessary measures required to prevent or control the risk from exposure to legionella bacteria. The risk assessment is carried out by or on behalf of the Duty Holder. The Duty Holder is identified as the employer; or a self-employed person; or the person who is control of premises or systems where others may be affected, such as in landlord/tenant situations or public premises.

The Duty Holder should appoint a competent person (or persons) to help undertake the measures needed to comply with the requirements in COSHH. The ACoP, L8, Paragraph 49 states that those appointed to carry out the risk assessment should have such ability, experience, instruction, information, training and resources to enable them to carry out their tasks competently and safely.

The risk assessment should identify and evaluate potential sources of risk and in particular:

  • the means by which exposure to legionella bacteria is to be prevented; or
  • if prevention is not reasonably practicable, the means by which the risk from exposure to legionella bacteria is to be controlled.

The assessment of risk for this report is based on site observations of the system(s) design and operation and from information provided by the relevant parties involved in the legionella control / water management programme. It takes into account the potential for legionella bacteria to contaminate the system(s), for legionella proliferation within the system(s), sources of aerosol formation, dissemination and the potential exposure to persons, the susceptibility of potential persons exposed and the adequacy of current control measures and management control procedures.

Where the assessment shows that there is a reasonably foreseeable risk and it is reasonably practicable to prevent exposure or control the risk from exposure, the duty holder should specifically appoint a competent person (or persons) to take day-to-day responsibility for controlling any identified risk from legionella bacteria, known as the ‘responsible person’. The responsible person should have sufficient authority, competence and knowledge of the installation and be suitably informed, instructed and trained. Training must be regularly refreshed and to a level that ensures tasks are carried out in a safe and technically competent manner.

Risk Assessment Status and Review

The ACoP, L8, requires that the risk assessment is a living document which must be regularly reviewed to ensure it remains up to date. The requirement to review the risk assessment may result when;

  • changes are made to the water systems;
  • changes are made to the use of the building in which the water system is installed
  • changes are made to the management and control systems;
  • further information is provided on the systems or control measures;
  • results show the risk control programme is not working effectively;
  • following reported or suspected cases of Legionnaires disease associated with the system.

Should none of the above occur which necessitate an update of the risk assessment then, First Environment Limited recommends that dependant on the risk ratings for the system(s), the risk assessment should be updated at least every one to two years.

Risk Assessment Ratings and Guidance

The risk assessment is based upon the likelihood of persons inhaling fine water droplets contaminated with Legionella bacteria. The assessment considers information as appropriate on (a) contamination; (b) amplification; (c) transmission; (d) exposure; and (e) host susceptibility

Each system included with the scope of works is considered in turn for the potential for the system to be colonised by Legionella bacteria; for the bacteria to multiply to significant numbers; for the bacteria to be formed into an aerosol; for the aerosol to be disseminated; for persons to be exposed to the aerosol; and for those persons to be susceptible to infection by the bacteria. These factors are based on inspection of the water system(s) and the key components and assets within each system(s) and, consider the design, operation and maintenance of the water system(s). Water management records are reviewed to assess the status and efficacy of the current control regimes and routes of communication and management processes are reviewed.

These factors are combined to produce a result comparable to the following simple risk assessment table. Whilst the worst case for persons exposed to Legionella bacteria is death, not all persons exposed will go onto develop Legionnaires disease. The actual risk to health (i.e. someone contracting Legionnaires’ disease or another form of Legionellosis, such as Pontiac Fever) will be dependent on the degree of exposure and the susceptibility of the individual. It should be noted that the attack rate of Legionnaires ’ disease for a normal population is about 1-2% and for a susceptible population is about 5%. These factors are taken into account when assessing the severity outcome by adjusting the standard severity scale to include evaluation of the potential for local infection of individuals or for a wider ‘outbreak’.

Legionella Control Association

The Legionella Control Association, developed jointly by the Water Management Society and British Association for Chemical Specialities, sets out auditable requirements for service providers. The aim of the code is to provide assurance to end users that the advice and services provided by registered companies are technically sound; identify lines of communication and responsibilities; and that staff employed to perform the actions are suitably trained. All registered Companies are externally audited by specialists from the legionella Control Association on an annual basis.

First Environment Limited is registered with the Legionella Control Association (LCA), for the provision of Legionella risk assessments, independent consultancy services, and training services. In compliance with our service provider commitments a copy of our registration certificate and the code can be accessed here.

Personnel utilised to undertake the Legionella risk assessment services have received in house training supported by external training certification including British Occupational Hygiene Society Legionella Proficiency Modules and / or City & Guilds Risk Assessment courses.

Further Advice

The Health and Safety Executive has published a leaflet, Legionnaire’s disease: A brief guide for duty holders (INDG458).  This can be obtained free of charge from the Health and Safety Executive web site http://www.hse.gov.uk/pubns/indg458.pdf and this site also provides access to further articles and information.

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