Understanding Your Legionella Risk Assessment

There is often a misconception that a Legionella Risk Assessment is just looking for the presence of Legionella; as if it’s a tick boxing exercise to state whether it’s there or not. However, a Risk Assessment of this kind is actually exactly what it states: it assesses not just whether Legionella is present, but what the risks are of the bacteria emerging. It’s about making sure your site is safe and recommending actions to reduce the risk from Legionella bacteria.

To give you guidance on what’s involved in a Legionella Risk Assessment and how you should use the report, we’ve answered some key questions:

What is a Legionella Risk Assessment?

During a Legionella Risk Assessment, we’re not looking for Legionella in the system, the assessment is instead designed to identify potential conditions that would encourage Legionella to grow. Then we recommend steps to eliminate or reduce that risk, making sure the site is as safe as it can be.

What causes Legionella?

There are three key elements that will encourage the growth of Legionella bacteria:

  • Temperature – Legionella likes temperatures between 20°C and 45°C. Therefore the best thing to do is avoid these temperatures. That means keeping cold water below 20°C and hot water above 50°C.
  • Stagnation – the infrequent use of taps or showers, or other devices where water does not flow through will encourage bacterial growth. Most common scenarios are vacant or disused areas of a building.
  • Nutrition – scale, corrosion, biofilm, algae or sediment in water systems all provide food for bacteria. These are the ideal sources of nutrition for Legionella and will help make a nice home for it to develop.

How is it harmful for humans?

The only way of contracting Legionellosis (disease caused by Legionella bacteria) is by breathing in small droplets containing the bacteria. Any form of aerosol poses a risk should Legionella be present in the system. This could be through spray from a tap or shower, process waters or cooling towers etc.

What will the Risk Assessment Report tell me?

A Legionella Risk Assessment will analyse the areas where the conditions encouraging bacterial proliferation can be found. It will look at the water tanks, water heaters and distribution pipework and determine whether the temperatures are right, how well the systems are being used and what nutrients are present to feed the bacteria. The assessment will identify areas where bacteria may be growing if it enters the system not whether the Legionella is present in the system at that moment.

Other areas are reviewed as well, such as occupants and whether they’re in a high risk group. The elderly or those with immune deficiencies are obviously more vulnerable. In addition, how Legionella can be disseminated in a form of aerosol is also reviewed, and management procedures that are currently in place are evaluated to see how effective they are.

The report will make recommendations on any control measures that are necessary to eliminate, reduce or manage the risk.

How detailed is a Legionella Risk Assessment?

A lot of data is analysed during a Risk Assessment. Everything from the number of showers to the plant inspection, along with all distribution pipework. It needs to cover all systems leaving no area omitted that could possibly cause harm. Therefore, it is very important that someone familiar with the building is available at the time of the assessment.

The Causal Chain

Legionella risk can be described as a chain of events. The job of the Risk Assessment is to determine whether any conditions are right for the chain of events to begin, and then it will make recommendations on how to break that chain. It’s not possible to eliminate water from buildings; we need it. Therefore recommendations are made on things such as adjusting water temperatures, removing scale or corrosion or replacing items that are too damaged to clean, and possibly removing showers or other devices that are no longer in use.

Taking Action

The report will list a number of recommendations. It’s not always possible to action them straight away, however responsible people have a legal duty to take reasonable steps to reduce any risks, and they must keep records to prove they have been actively trying to do this.

Taking into account all the factors, a score matrix is produced in the report that looks through the causal chain and will recommend what needs to be done. In the RM Risk Assessment, we recommend what needs to be done with a priority rating and we propose a timescale, easily highlighting which issues require urgent attention:

  • Intolerable risk – immediate action must be taken, as soon as possible
  • Substantial risk – action within 1 month
  • Moderate risk – action within 3 months
  • Tolerable risk – action within 6 to 12 months
  • Trivial risk – this isn’t a huge issue, but it’s good practice to remedy it

Who needs to take action?

Every site should have staff or key personnel who have the responsibility for going through the Risk Assessment and taking the necessary action. It is vital that this person or people are sufficiently trained. We recommend completing Legionella Awareness training as a minimum, or more advanced training where necessary. They must fully understand the Risk Assessment, what it’s purpose is, how important it is, and how to take action on the results of the report.

The RM Risk Assessment

At RM, we have some additional elements to our Risk Assessments, and we use them alongside our HASAD system as that allows for the recommendations to be signed off and managed more easily. A record must be kept by the responsible person(s) to show what has been done and prove that all reasonable steps have been taken to reduce risks.

How often does the Risk Assessment need to take place?

Guidance from the Health and Safety Executive (HSE) states that Risk Assessments should be reviewed regularly and be kept up to date following any changes. This could be changes to the building use, system, plant or significant changes to key personnel. In addition, if the building has control issues or someone has contracted Legionella then the Risk Assessment needs to be reviewed.

Once all the issues have been addressed, it may be that a site is awarded as “low risk”. However, even in these cases, and if nothing changes, we recommend that Risk Assessments are completed every 1 to 2 years. It is vital to always be cautious.


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