Legionella Risk Assessment

What is Legionella?

Legionella is a bacteria which is common in natural water courses such as rivers and ponds. Since legionella bacteria are widespread in the environment, they may contaminate and grow in other water systems such as cooling towers and hot and cold water services.

They survive low temperatures and thrive at temperatures between 20-45°C if the conditions are right, e.g. if a supply of nutrients is present such as rust, sludge, scale, algae and other bacteria. They are killed by high temperatures.

What is Legionnaires’ disease?

Legionnaires’ disease is a potentially fatal pneumonia caused by legionella bacteria. It is the most well-known and serious form of a group of diseases known as legionellosis. Other similar (but usually less serious) conditions include Pontiac fever and Lochgoilhead fever.

Infection is caused by breathing in small droplets of water contaminated by legionella bacteria. The disease cannot be passed from one person to another.

Everyone is potentially susceptible to infection but some people are at higher risk, e.g. those over 45 years of age, smokers and heavy drinkers, those suffering from chronic respiratory or kidney disease, and people whose immune system is impaired.

Duties of Employers

Under general health and safety law, employers have to consider the risks from legionella that may affect employees or members of the public and take suitable precautions.

An employer or a person in control of premises (e.g. a landlord) must:

  • Identify and assess sources of risk.
  • Prepare a scheme (or course of action) for preventing or controlling the risk.
  • Implement and manage the scheme – appointing a person to be managerially responsible, sometimes referred to as the ‘responsible person’.
  • Keep records and check that what has been done is effective.
  • If appropriate, notify the local authority that you have a cooling tower(s) on site.

Assessing the Risk of Legionella

An employer or person in control of premises is responsible for carrying out a risk assessment. An employer may be able to carry out the assessment yourself but, if not, help and advice should be sought from outside consultancies, like Arinite.

In assessing the risk the following need to be considered:

  • Are conditions present which will encourage bacteria to multiply? For example, is the water temperature between 20-45°C?
  • Is it possible that water droplets will be produced and, if so, could they be dispersed over a wide area? For example, consider showers and aerosols from cooling towers.
  • Is it likely that anyone particularly susceptible will come into contact with the contaminated water droplets?

Water Systems at Greatest Risk

Cooling towers, evaporative condensers and hot and cold water systems have been associated with outbreaks. Other potential sources where precautions might be needed include humidifiers and spa baths.

If it is decided that the risks are insignificant, then the assessment is complete. No further action is required other than to review the assessment periodically in case anything changes in the water system.

Managing the Risk of Legionella

Someone needs to be appointed to take responsibility for managing legionella risk control measures.

The ‘responsible person’ needs to be competent – that is, they need to have sufficient knowledge and experience to enable them to manage and control the risks effectively.

If contractors are appointed to carry out water treatment or other work, it is still the responsibility of the appointed person to ensure that the treatment is carried out to the required standards. Before a contractor is employed, they should be checked to ensure that they can do the work to the required standard.

Further Information on Legionella

More detailed guidance on the duties of employers can be found in the Approved Code of Practice and guidance Legionnaires’ disease: The control of legionella bacteria in water systems. Approved Code of Practice and guidance L8 (Third edition) HSE Books 2000 ISBN 978 0 7176 1772 2. Part 1 of this publication contains advice on legal duties. Part 2 contains guidance on technical aspects of the assessment and control of legionella risks.

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Health and Safety Advice