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How Do I Do a Legionella Risk Assessment?


If you are responsible for water systems that workers or residents are exposed to, then you have a legal duty under UK health and safety legislation to control the hazard of legionella bacteria. As part of this mandate, you are required to conduct a legionella risk assessment.

The disease caused by Legionella is potentially fatal. It’s caused by the inhalation of small water droplets containing legionella bacteria (Legionella pneumophila).

All man-made water systems could potentially grow this bacteria. In particular, this is true if conditions are suitable.

In this article, we will examine how to prevent this from happening. We will look at what you need to know about the risk of legionella and how and when to perform a legionella risk assessment.

Do I need a Legionella Risk Assessment?

Yes, you need to conduct legionella risk assessment in your workplace. It is a legal requirement under the following legislation:

Can You Do a Legionella Risk Assessment Yourself?

The Health and Safety Executive (HSE)’s HSE ACoP L8 The Control of Legionella Bacteria in Water Systems states that the duty holder can carry out the risk assessment themselves provided they are competent.

A competent person is defined as somebody who has suitable knowledge, skills, and experience. So, in terms of undertaking a Legionella risk assessment – examples of these three elements would be:

Knowledge – they should have Legionella awareness

Skills – they have undertaken this type of risk assessment exercise before and know how it operates in practice

Experience – they have undertaken risk assessment exercises on water systems similar to those in question. So for example someone who has only ever undertaken a risk assessment of a simple water system in a small building would not have suitable experience for undertaking a risk assessment on a large complex industrial plant

Alternatively, you can seek help in undertaking the risk assessment – possibly via a contractor. In this case, you must carefully check the competence of the person they are appointed for the risk assessment task.

Simple vs Complex Water Systems

In the eyes of the law, you are considered competent to conduct risk assessment depends upon the understanding of the water system under control.

For a simple, domestic water system, HSE advises you can perform risk assessment yourself by following the proper guidance. However, for complex water systems such as cooling towers and commercial water supplies, you certainly need an expert (competent person) with a background in such systems for conducting the legionella risk assessment and management process.

Are there Legionella Risks in my Workplace?

Every premises carries the risk of Legionella. The health risks associated with Legionella bacteria are significantly increased in areas where water is stored, where the water temperature ranges between 20° and 45° Celsius, where breathable water droplets can be spread in the form of aerosols, or where there is a source of nutrients (sludge, bio-films, organic matter) for the bacteria to grow.

How Often Does a Legionella Risk Assessment Need To Be Done?

Legionella risk assessment should be considered as a living document which should be reviewed regularly to ensure it remains up to date, according to the Approved Code of Practice, L8.

The industry precedent is that this risk assessment should be carried out at least every two years. But, this is time period is not valid in all situations. There are certain situations when an assessment is required sooner, these are:

  • When the site’s population falls within the high-risk category (See below)
  • When changes are made to the water system

How a Legionella Risk Assessment is Conducted

Desktop Appraisal

As part of your risk assessment, you should begin with a desktop appraisal of all relevant documentation. This will include looking at:

Assessment of the safe operation of the system: The written control scheme must explain, in detail, how the water system should be operated to control the risk from legionella.

Assessment of the maintenance and testing records: The risk assessment should appraise any records of the maintenance and testing records to evaluate how well the necessary controls are being implemented.

Assessment of management responsibilities: The written control scheme must clearly document the management responsibilities for all parties involved.

Assessment training records and competence checks of site staff and contractors: How competent are those involved in controlling water systems? Have they undertaken training such as Legionella Awareness Training?

After completing a desktop assessment, work through the five-step process of risk assessment.

Step 1 - Identify the Hazards

An electrical permit to work certifies that a circuit or a piece of equipment is not live and is safe to work on. Before an electrical permit to work can be issued any electrical equipment or circuitry must be isolated and, where appropriate, earthed, according to HSE guidelines.

This particular permit cannot be used to authorise work on any circuitry or equipment that is live. It must contain details on measures taken to disconnect, isolate, prove dead, earth, and lock off the power source. Details on the equipment to be worked on, any adjacent equipment, and the warning signs that have been posted must also be included.

Step 2 - Decide Who Might be Harmed & How

Consider how many people might be exposed to legionella. For example is the premises in the middle of a busy inner-city, or, located in a sparsely populated remote area?

Also, are there people who are in higher-risk categories – these will include:

  • Men – fewer women catch the disease
  • People over 45 years of age
  • Smokers
  • Those suffering chronic respiratory ailments like asthma
  • Anyone with an impaired immune system – so this would include:
  • Cancer patients
  • Alcoholics
  • People suffering from kidney disease
  • Diabetics

Step 3 - Evaluate Risks

This step is all about deciding whether there is a problem and if there is, what needs to be done to control it. This relies on the evaluation of risk.

Risk is the probability of harm occurring combined, with the consequences or outcome if the harm should it occur. So, let’s look at what this means from a Legionella point of view: Consider the factors we have said give rise to the Legionella hazard.

  • Contamination, is there any evidence of this, if so, how significant?
  • Amplification
  • Do the temperature monitoring logs show any breach of required temperatures and if so, by how much and how often?
  • Are there any signs of stagnation if so, how significant are they?
  • Nutrients, are all areas to the system clean? And if they’re not, how bad is the fouling?
  • Are the current risk controls working for this aspects?

This is why the risk assessment began by conducting a desktop appraisal of the existing control measures

Step 4 - Decide on Precautions

Where the risk assessment shows that there is a significant risk then suitable precautions must be implemented. Following is the hierarchy of risk and controls which underpin health and safety legislation:

Eliminate the hazardthis is the most effective and preferred way of controlling risk. For example, if there is a blind end that poses a risk of stagnation – this should be completely removed by cutting the pipework back to the main system.

Reduce the hazard is the next preferred option. So here, the hazard remains but the risk from it is reduced by controlling it or substituting with a lower risk option. For example – a thermostatic mixing valve built into a tap reduces the hazard of lower hot water temperatures as opposed to one location several meters prior to the outlet

Preventing people from coming into contact with the hazard is the third level of control is to accept the hazard as it is but to physically prevent people from coming in contact with it. So for the testing of emergency showers could be undertaken when an area has been evacuated and cordoned off.

Safe systems of work is the 4th level of controls are safe systems of work – or ensuring that people act or behave in ways that control the risk at an acceptable level. This type of control is fundamental to the safe operation of a water system and covers activities such as temperature monitoring and cleaning regimes.

Personal protective equipment, or PPE, is the least preferred level of risk control. From a Legionella point of view, PPE will not be widely used but may have some limited uses – for example to respirators to protect individuals investigating a potential outbreak of Legionella.

Step 5 – Record Your Findings & Then Do It

Recording a risk assessment in all but the smallest of operations is a legal requirement. If something goes wrong, or, you are visited by enforcing authorities then they will expect to see a copy of your risk assessment and it must be available for inspection

It is highly unlikely that a risk assessment will not identify a requirement for improvements – but if this should occur it is still important to record your findings so that there is documentary evidence that the assessment was undertaken.

Final Words

Legionella is a serious disease that every business should be aware of. You being an employer have the legal duty to control the legionella risk from widespread. This requires you to conduct legionella risk assessment in your workplace. This risk assessment process must be done by the responsible person. There is a wide range of providers that offer online health and safety training on legionella control. However, Human Focus’ Legionella awareness course is the best choice for organisations of any size.

About the author(s)

Amina Saeed
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