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Your guide to Legionella Risk Assessment for Duty Holders For Commercial Property

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Call Comfort Services Group today on 01206 247010
What is Legionella?
Legionella Compliance (The Law)
Your Responsibilities
Latest News
Water system at college salon has been linked to outbreak of Legionnaires' disease

The water system at a hairdressing salon in North Lincolnshire College has been identified as the likely source of an outbreak of Legionnaires' disease which put two women in hospital.

Fears mount of another Legionnairesí outbreak as toll hits 80 after eight more people are diagnosed with the deadly disease

Leading Legionnaire’s expert claimed cash-strapped firms were deliberately falsifying safety logs and said the practice could have devastating consequences. Find the original article HERE.


Company must pay £1.8m after risking Legionnaires for six years

The cash management arm of multi national security firm has been fined £1.8m after its failure to manage water systems at its office in Essex for around six years, risked exposing staff to legionella.


How Comfort Services Group Ltd can help you

As a commercial landlord it is your responsibility to manage legionella risk and ensure that regular risk assessments are completed. At Comfort Services Group Ltd we are able to take the stress out of Legionella risk management with a complete, professional service. Our engineers are highly experienced in carrying out legionella risk assessments on commercial properties and can advise on a programme of risk assessment and testing that will ensure you meet all necessary laws and legislation.

Comfort Services Group Ltd are experts in the commissioning and testing of water systems and, with over 13 years’ experience, will ensure that your regular risk assessments are completed accurately and in-line with legal guidelines. The aim of any testing is to help identify any areas of a system that may require improvement to minimise the risk of legionella. Our thorough system testing is followed by a concise report detailing system performance and any work required to bring the system in line with recommended standards. The amount of work that a system is likely to require off the back of an assessment will, typically, be directly proportional to its’ overall size and complexity. Whilst a simple, low level water system will be at lower risk, it is just as important to ensure that that Legionella risk assessments and testing are carried out regularly. This will ensure that your legal and regulatory obligations as a landlord are met. The period between risk assessments will vary depending on your properties system, however, at Comfort Services Group Ltd, we recommend that a risk assessment be carried out on a water system at least every two years regardless of its’ size or complexity. If you need advice or want to know more about the requirements for your property then please do not hesitate to get in touch.

Where a high concentration of Legionella is identified, we can offer advice and solutions to the successful reduction of these volumes. It is important, when legionella is identified, that a suitable internal procedure be setup for water sampling and water management. We can advise on the most suitable methods of testing and recording to help ensure that your obligations (legal and regulatory) as a landlord are met.


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What is Legionella?

Legionella is most commonly known for being the main cause of Legionnaires' disease (of which there have been a number of high-profile outbreaks in recent years). The bacteria can also cause the spread of other diseases such as Pontiac fever. Legionella is a fast-growing bacteria which can grow and multiply in water systems which is why it is essential that regular risk assessment and testing be carried out. Legionnaires' disease is an acute infection, primarily affecting the lungs, with symptoms closely resembling those of pneumonia.

During the early stages of Legionnaires' disease, a sufferer is likely to demonstrate, more mild, flu-like symptoms such-as:

  • Aches and pains of the muscles
  • Fluctuations in temperature
  • Headaches (mild)
  • Feelings of confusion or fatigue

It is important that, once identified, Legionnaires' disease is treated quickly as the bacterial infection can continue to grow, causing more serious symptoms. Sufferers of advanced Legionnaires' are likely to experience difficulty in breathing and chest pains. A persistent cough is a typically symptom of advanced Legionnaires' which may be accompanied by the coughing up of phlegm, or in worse cases, blood.

What is Legionella? (Cont.)


Understanding the nature of Legionella, how it grows and develops and how Legionnaires' disease is contracted and spread allows us to best undertake legionella risk assessments and testing.

Legionella comprises of a group of naturally occurring bacteria (most commonly of the L pnemophila species). A low level of legionella bacteria can be typically found in most naturally occurring bodies of water including ponds, lakes and rivers. The level of naturally-occurring legionella is typically too low to cause a risk to humans. It is when the legionella bacteria is found in man-made water systems that the risk of human infection increases significantly. The reason behind this increased risk is that the conditions found within man-made systems are often ideal for the incubation and multiplication of legionella bacteria.

Infection from Legionella bacteria in humans occurs when the bacteria is inhaled. Because of this, the highest risk comes from open systems (such as air conditioning units) where the bacteria is contained within the minute droplets of water discharged from the system. Once again, the size and complexity of a water system will have a direct correlation with the level of risk. A simple, domestic water system will provide less opportunity for the incubation and rapid growth and reproduction of legionella when compared to a complex commercial one. In addition to improved incubation conditions, a commercial system carries a higher risk of infecting a larger number of people and causing a large-scale outbreak/epidemic. It is this higher level of risk, as well as the consideration of legal regulation and liabilities, which make regular testing and risk assessments in commercial properties an essential consideration.


Is your property at risk from Legionella?


There is a risk of Legionella in almost every building which operates hot and cold water systems. There are a number of key factors which determine the level of legionella risk and, at Comfort Services Group, we can help you to assess the level of risk in your property’s system and put measures in place to reduce/limit this risk. One of the most important considerations when undertaking legionella risk assessment is the complexity of the water system. Whilst a simple, domestic cold water system presents a relatively low risk, a complex, open air conditioning system (such as those in large commercial buildings) can offer ideal incubation conditions for legionella bacteria. Regardless of the type and complexity of the system in your premises however, it remains important that regular risk assessment and legionella testing be completed to comply with mandatory laws and regulations.

The design of a water system is another important consideration when assessing risk. A poorly designed or inefficient system is liable to present a higher risk and, through thorough system testing, we can recommend improvements to the system to improve efficiency and reduce the risk of legionella. We also provide a pre-commissioning analysis of hot and cold water systems. This in-depth system analysis allows our experienced engineers to highlight areas where pre-emptive work may be carried out to reduce future risk of legionella.

Asides from its’ basic design, the materials or, more specifically, the quality of materials used in a system can have a significant effect on legionella risk. Materials which are prone to deterioration present an increased legionella risk. Impurities such as lime scale, rust or algae can act as a nutrient for the legionella bacteria, encouraging multiplication. In older systems it is important to ensure that any parts showing signs of corrosion or deterioration are, therefore, renewed or replaced as soon as possible,

Legionella bacteria will incubate and multiply only at temperatures between 20 and 45 degrees C. The risk of legionnaires and other related diseases can therefore be reduced or eliminated by ensuring that hot water systems operate continually above 50C and cold water is kept below 20C.


Legionella Compliance (The Law)

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It is the person responsible for a commercial premises that is legally required to ensure that regular and suitable legionella risk assessments and testing are carried out. In the instance of a commercial premises, this liability typically falls to the landlord. As the landlord it is your responsibility that, asides from regular risk assessments, complete and accurate records are kept of all testing. Comfort Services Group Ltd can help to take the stress out of legionella risk assessments by ensuring that your legal obligations are met and that record keeping complies with all necessary regulations.

As landlord, the regulations state that it is your responsibility to identify any potential sources of legionella and demonstrate that all risks have been correctly managed, either through control or prevention. Failure to comply with legionella regulations (either by failing to carry out a suitable risk assessment, failure to record data correctly or failure to take appropriate action where a risk is identified) can make you liable for prosecution or a substantial fine.


According to the Health and Safety Executive: “Under general health and safety law, as an employer or person in control of a premises, you have health and safety duties and need to take suitable precautions to prevent or control the risk of exposure to legionella. Details of the specific law that applies can be found in part 1 of Legionnaires’ disease:

Carrying out a risk assessment is your responsibility and will help you to establish any potential risks and implement measures to either eliminate or control risks. You may be competent to carry out the assessment yourself but, if not, you should ask someone with the necessary skills to conduct a risk assessment. This can be done by someone from within your own organisation or from someone outside, e.g. an external consultant.”

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Your Responsibilities

Identification of of risk

The level of Legionella risk can vary significantly between water systems depending on their design, construction and complexity. However, regardless of the level of risk, it is essential that regular risk assessments are carried out to comply with your legal and regulatory obligations. At Comfort Services Group Ltd, we recommend that, as a minimum, legionella risk assessments are completed every two years (and more frequently for higher risk systems such as complex air conditioning systems).

Often, low risk systems will require little or no preventative or control work but must still be subject to regular assessments. Systems which have a higher risk may require immediate work to reduce levels of legionella and help prevent a potential outbreak of legionnaire’s disease. Systems most at risk of harbouring and incubating legionella bacteria include: 

  • Systems which store water or recirculate the same water within a closed system
  • Systems which actively release water droplets into the atmosphere
  • Systems with an operating water temperature of between 20-45°C
  • Systems susceptible to contamination from rust or other particles

Management of risk

Once risk has been identified, it must be then managed (regardless of the level of risk identified through the risk assessment). Risk management may be delegated to a third party providing they have the appropriate experience, skills and system knowledge.

Comfort Services Group Ltd carry out risk management for a number of clients relieving the client and their staff of this responsibility. Why not contact Comfort Services Group Ltd today to find out how we can help identify and manage Legionella risk for your commercial property.

Prevention and control of risk

The prevention of legionella may be possible without the need for control measures and systems to be put in place. The first consideration is whether it is possible to completely eliminate the risk of Legionella without the need for control measures. This will be largely dependent on the required specification and type of system needed. If the risk of Legionella cannot be completely eliminated then it is necessary for control measures to be implemented which effectively limit the risk of legionella and associated diseases.

HSE guidelines require that, where a risk of legionella is present in a system, that sufficient controls are implemented to ensure that this risk is managed. At Comfort Services Group Ltd we assist with the whole process, from identifying areas of a system which may present a Legionella risk to advising on preventative measures. We can also carry out further testing and advise on reporting and the keeping of records to comply with necessary legislation.

As landlord and the person in charge of the premises, it is important to understand your personal responsibilities with regards the risk assessment and control of legionella. Procedures need to be put in place for the assessment and, where required, implementation of a control scheme. This can be managed by yourself, a colleague or a third-party (such as Comfort Services Group Ltd) but it is your responsibility to determine who is responsible for this. We recommend assigning a third party with the experience and system knowledge required to alleviate the burden on this responsibility.

At Comfort Services Group Ltd we can also help you to keep accurate records which are essential to meet necessary HSE regulations. These records include the nature and frequency of testing, observations made and any reparatory work undertaken. Contact Comfort Services Group Ltd today to find out how we can help with your legionella risk assessment and control.

Example tasks and how often they should be carried


  • Check calorifier flow temperatures 
  • Take temperatures at sentinel points
  • Take temperatures at return legs of principal loops (sentinel points) to confirm they are at a minimum of 50 °C
  • Check temperatures at sentinel taps (typically those nearest to and furthest from the cold tank, but may also include other key locations on long branches to zones or floor levels).


  • Dismantle, clean and descale
  • Take temperatures at return legs

6 Monthly

  • Purge any debris in the base of the calorifier to a suitable drain
  • Check water temperatures to confirm the heater operates at 50–60 °C (55 °C in healthcare premises) 
  • Flush through and purge to drain


  • Inspect calorifier internally by removing the inspection hatch or using a boroscope and clean by draining the vessel.
  • Take temperatures at a representative selection of other points
  • Inspect the integral cold water header tanks 
  • Inspect cold water storage tanks
  • Check the tank water temperature remote from the ball valve and the incoming mains temperature
  • Take temperatures at a representative selection of other points to confirm they are below 20 °C
  • Check thermal insulation 
  • Inspect, clean, descale and disinfect any strainers or filters associated with TMVs