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Legionella risk assessment and control measures

Updated: Feb 16

The topic of legionella has hit the headlines again with a very heavy fine being imposed on G4S for health and safety failings at its site in Harlow.

In 2013, environmental health officers followed up a report that a worker had contracted legionella and although they could not prove that he had caught the disease on site, their inspection uncovered serious compliance irregularities in the way that the water systems were maintained. Monitoring and testing were erratic and staff had not been trained properly.

There were no up-to-date policies or risk assessments in place. No steps had been taken to reduce the risk of Legionnaires’ Disease, despite extensive guidance and the advice of consultants and environmental health officers.

A prosecution began and in June 2016, G4S pleaded guilty to two charges under the 1974 Health and Safety at Work Act.

In September, at the sentencing, a judge fined G4S £1.8 million and also ordered them to pay costs of £34,000. Had they not pleaded guilty, the fine would have been nearly twice as much.

It can be seen that the outcome of poor management of the risks of legionella can be very serious indeed.

What is legionella?

Legionella bacteria are organisms which live in aquatic environments such as rivers, lakes and reservoirs as well as hot and cold water storage tanks which supply showers, wet air-conditioning systems, sprays and taps etc. If they are breathed in via water droplets in the air, they can lead to Legionnaires’ disease, a potentially fatal form of pneumonia.

The most susceptible are the elderly, the young, those who are ill, persons taking immune-suppressants, smokers etc.

The disease has flu-like symptoms including high fever, chills, and headache and muscle pains. In most cases, the disease can be effectively treated with antibiotics. However, it can be fatal for those in susceptible groups.

Below 20 degrees C, the organism does not appear to multiply and it is killed by temperatures of 60 degrees C and above.

Assessment and control of risk

Those in charge of water systems need to make sure that a risk assessment is carried out to ensure the protection of their workforce and others. They should look at measures which provide protection for the presence of vulnerable groups and individuals (elderly, young, immune-compromised).

Measures to control the risk should include:

  • Not allowing the proliferation of the organism in water systems.

  • Reducing, as far as reasonably practicable, the exposure to water droplets and a aerosols.

  • Regular cleaning and disinfection of spray heads, spray taps etc.

  • Control of water temperatures.

  • Cleaning and disinfection of water systems.

A foreseeable risk of exposure to Legionella bacteria exists from:

  • Water systems in cooling towers.

  • Water systems used for cooling using evaporative condensers.

  • Hot and cold water systems.

Other water-containing plant and systems which are above 20 degrees C and under 60 degrees C and may release spray, droplets or aerosols when used or maintained.

To prevent the proliferation of the bacterium, there are specific control measures (involving cleaning, disinfection, treatment and sampling) for systems incorporating cooling towers, wet air conditioning systems, spa baths and pools, indoor fountains, car/bus washers etc.

The person who installed your system or a company/competent person can evaluate the risk of legionella if further advice is needed. Simpler systems such as hot and cold water supplies where the risk from Legionella is lower e.g. small domestic-type hot and cold water systems with high turnover, simple pipe-runs and high water temperature may require little or no risk control. Advice should be sought from a person competent in legionella precautions.

How to Complete the Risk Assessment

Risk assessments are not something that should be done once and forgotten about.

Employees should know where they are located and what is contained within them. This is particularly relevant where employees need to take action to protect their own safety e.g. wearing personal protective equipment, following a work procedure etc.

Risk assessments should be reviewed to ascertain if they are still suitable and sufficient on the following occasions:

  • On a regular basis (e.g. every 12 months)

  • Where there are new employees, new equipment or new substances introduced into the workplace.

  • Where there has been an accident or near miss. This is to ensure these were not due to inadequacies in the risk assessment.

  • Changes to legislation or health and safety good practice advice e.g. the safety classification of some materials may change due to increased medical knowledge.

Once reviewed, the risk assessment should be changed to reflect the new circumstances or, if suitable, initialled and dated to show that the risk assessment still applies.


Who can we appoint to test or monitor Legionella?

Anyone, provided they have the relevant skills to implement the control measures and strategies, i.e. they are suitably informed, instructed, trained and assessed. They should be able to ensure that tasks are carried out in a safe, technically competent manner in line with current regulations.

Would Legionnaires’ be reportable?

If you have a case of legionellosis in an employee who has worked on cooling towers or hot water systems that are likely to be contaminated with legionella, you have a duty to report this under the Reporting of Injuries, Diseases and Dangerous Occurrences Regulations (RIDDOR).

Who can help me manage the risk from legionella?

You have a duty to appoint a competent person to help you with your responsibilities in complying with the regulations. The person must be competent by having the knowledge, skills and experience in this field and can be: you, one or more of your employees, or you could bring someone in from outside your company (contractor).

Would the cleanliness of the tank make any difference?

Yes, legionella is less likely in a clean tank. By having a dirty tank, there are sources of nutrients such as rust, sludge, scale and organic matters for the bacteria.

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