What Is Legionella Risk Assessment?

what is legionella risk assessment

Employers must identify, evaluate and control workplace hazards – a process known as risk assessment.

The detail, number and type of risk assessments needed depend on the hazards specific to your workplace. A Legionella risk assessment is necessary if your premises have a water system.

What is Legionella risk assessment? It reviews your water systems, determines the risk level of bacterial growth and lets you plan appropriate controls.

Legionella assessments require specialist water system knowledge, which some employers lack. If you’re unsure how to assess Legionella risks or how to decide on controls, this guide offers an overview. It also advises what to do if you feel unsuited to personally complete the assessment.

What is Legionella?

Legionella is a strain of bacteria responsible for Legionellosis ­– a collection of lung conditions including Pontiac fever and the more severe Legionnaires’ disease. It’s common, naturally being found in freshwater bodies.

Infection risks are extremely low in the wild, however, since conditions are rarely favourable for Legionella growth. Legionellosis is also almost exclusively caused by breathing in infected water droplets, which rarely happens organically.

Workplaces don’t share these natural defences. Legionella bacteria in a human-made water system is a significant threat. It thrives in tepid stored water and feeds off the chemical deposits and substances in poorly maintained systems.

If contaminated water is turned into respirable water droplets (aerosols) – through showers, hot tubs and cooling towers, for example ­– then people are at risk of infection.

Legionnaires’ Disease

Legionella bacteria is linked to several diseases, but Legionnaires’ is the most dangerous. Pontiac and Lochgoilhead fever, which round out the Legionellosis family, feel similar to mild flu and usually only need a few days of rest to get over. Legionnaires’ disease is more serious.

Legionnaires’ disease

As a form of pneumonia, Legionnaires’ disease primarily affects your lungs. It can also cause gastrointestinal issues or affect cognition. The disease usually reveals itself two to three days after inhaling Legionella-infected aerosols, with muscle aches being common early indicators. Other signs include:

  • A persistent, dry cough
  • Shortness of breath for no apparent reason
  • Chest pain, particularly when breathing or coughing
  • A high temperature or fever (over 40°C)
  • Headaches
  • Confusion
  • Fatigue
  • Nausea or vomiting
  • Diarrhoea

Legionnaires’ disease always requires medical treatment. Every patient needs antibiotics and more severe cases necessitate hospitalisation, where critical patients can be given oxygen or put on a ventilator.

Most people fully recover from a bout of Legionnaires’, although it can prove fatal. European Centre for Disease Prevention and Control data suggests that Legionnaires’ disease is deadly in around 10% of cases, with smokers or those with underlying conditions being particularly vulnerable. Adults over 50 are also at increased risk due to the natural weakening of our immune systems as we age.

Legionella Awareness Training

Need training for Legionella to control the risk of this bacteria at work? Human Focus offers an online Legionella Awareness Training course, which is designed to examine the health risks associated with legionella bacteria and ways to control it to ensure safety for all.

When are Legionella Risk Assessments Necessary?

Legionella bacteria is a recognised health hazard, so you’re legally required to protect against it. This obligation makes Legionella assessments necessary for any premises with a water system.

Not every system will require an in-depth risk assessment or extensive Legionella risk controls. They vary in size, complexity and features.

You also don’t need to document your risk assessment if you have fewer than five employees. But you must still go through the process to ensure your systems are safe.

Relevant Legislation

All workplaces are subject to the Health and Safety at Work etc. Act 1974 (HSWA). The HSWA underpins occupational safety in the UK and requires employers to protect workers, visitors and members of the public from harm on their premises. This duty extends to Legionella management.

The Control of Substances Hazardous to Health (COSHH) is also applicable. COSHH provides the legal framework for assessing, preventing and controlling bacterial risks, including Legionella.

Finally, you should know the Legionnaires’ Disease Approved Code of Practice (ACOP). ACOP doesn’t place any duties on you as an employer. Instead, it outlines how to comply with the Legionella control regulations in the HSWA and COSHH.

Who is Responsible for the Risk Assessment?

Employers or those in control of premises are responsible for Legionella risk assessments. You’re a ‘person in control of a premises’ if you have the authority to make management decisions about the property. This group includes landlords, building managers and managing agents.

However, a Legionella risk assessment requires specialised knowledge, which many employers lack. When an employer (or other duty holder) recognises they cannot safely complete the risk assessment, they can delegate it to another employee or contractor.

Delegation is often advisable as some risk assessments are complex and demand in-depth knowledge of water systems.

While you can delegate the execution of a risk assessment, you can’t discharge the responsibility. Suppose a risk assessment is insufficient and harm comes to someone on your premises. In that case, you are then legally accountable for whether or not you completed the risk assessment.


Anyone who conducts the risk assessment must be competent. Competency means having the proper knowledge, skills and experience to safely complete the task.

You must know you are competent before tackling any Legionella risk assessment, or you may breach Legionella control regulations. If you allocate the duty to someone else, you must determine their competence.

How do You Carry Out a Legionella Risk Assessment?

Employers must also provide PPE and instruct workers on its proper use if required. It’s also necessary for employers to replace or repair any PPE in poor condition.

A Legionella risk assessment follows the same basic structure as any other:

  1. Identify hazards
  2. Evaluate risk levels
  3. Implement controls
  4. Record your findings
  5. Review and adjust as needed

You can find more detailed advice from the Health and Safety Executive (HSE), but we’ve outlined the steps below.

Identify and Evaluate Risks

You must understand your water system to identify every hazard and determine who’s at risk. Workplaces and systems are different, but common risk factors to look out for include:

  • Water is maintained between 20–45°C (Legionella’s preferred temperature range)
  • Water is stored or re-circulated
  • Deposits of rust, sludge or other organic matter are present (these feed bacteria)
  • Features such as cooling towers or showers are part of the system (these create aerosols)
  • Occupants are particularly vulnerable to infection due to age, underlying conditions, etc

Implement Control Measures

You must decide on sufficient control measures after identifying the hazards and evaluating risk levels. If you can eliminate the risk entirely, do. But that’s not always possible, so find ways to maintain and operate your water system that limits Legionella growth.

Proven risk controls include:

  • Maintaining water at safe temperatures (below 20°C for cold, above 60°C for hot)
  • Preventing stagnation by reducing pipe lengths
  • Cleaning the system and the water in it regularly
  • Using approved materials that suppress Legionella growth in your system

Record Your Findings

This step is only mandatory if you employ more than five people. Regardless of business size, it’s always wise to record your assessment as it helps planning and proves compliance.

You should document:

  • The person conducting the risk assessment
  • Significant findings
  • Written risk control schemes and how they’ll be implemented
  • The state of the water system being assessed

Review Your Controls

After your control systems are in place, you must review them to confirm they work. It’s also necessary to return to your risk assessment if your workplace undergoes any significant changes in:

  • Staff
  • Operations
  • Premises

Any Legionella-related incidents or near misses should prompt an immediate review, too.


No further action is needed if your initial assessment finds Legionella risks particularly low.

Examples of a low-risk environment include:

  • Small buildings without occupants are specifically vulnerable to Legionella
  • Water is flushed through the system regularly
  • Cold water exclusively comes from the mains (so it’s never stored in the system)
  • Hot water comes out of taps above 50°C
  • Water systems only feed toilets and basins (so there’s negligible risk of aerosols)

Legionella Training

Unless you work with water systems, you probably lack the expertise to complete a Legionella risk assessment safely. If this describes your situation, appointing someone else to do the work is better. But delegation comes with its own issues.

Determining a contractor’s competency level or understanding of recommended control measures can be challenging without knowledge of Legionella risks. It’s also difficult to communicate the findings to employees or ensure the assessment is followed after the contractor has moved on.

Our online Legionella Awareness course covers the health risks and symptoms of Legionnaires’ disease and what makes someone vulnerable. It also provides an overview of Legionella hazards and proven control measures. This level of knowledge alone probably won’t prepare you to conduct your risk assessments. But it will help you judge a contractor’s competency, maintain control measures and protect employees from ongoing Legionella risks.

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Jonathan Goby
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