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Legionella Temperature Monitoring













Managing the risk

As an employer, or person in control of premises, you must appoint someone competent to help you meet your health and safety duties and to take responsibility for controlling any identified risk from exposure to legionella bacteria. A competent person, often known as the responsible person, is someone with sufficient authority, competence, necessary skills, knowledge of the system, and experience. The appointed responsible person could be one, or a combination of: 

  • yourself

  • one or more workers

  • someone from outside your business

If there are several people responsible for managing risks, eg because of shift-work patterns, you must make sure that everyone knows what they are responsible for and how they fit into the overall risk management of the system.

If you decide to employ contractors to carry out water treatment or other work, it is still the responsibility of the competent person to ensure that the treatment is carried out to the required standards. Remember, before you employ a contractor, you should be satisfied that they can do the work you want to the standard that you require. There are a number of external schemes to help you with this, for example, A Code of Conduct for service providers . The British Standards Institute have published a standard for legionella risk assessment


Preventing or controlling the risk 

You should first consider whether you can prevent the risk of legionella by looking at the type of water system you need, eg identify whether it is possible to replace a wet cooling tower with a dry air-cooled system. The key point is to design, maintain and operate your water services under conditions that prevent or adequately control the growth and multiplication of legionella. 

If you identify a risk that you are unable to prevent, you must introduce a course of action ie a written control scheme, that will help you to manage the risk from legionella by implementing effective control measures, by describing: 

  • your system, eg develop a schematic diagram

  • who is responsible for carrying out the assessment and managing its implementation 

  • the safe and correct operation of your system 

  • what control methods and other precautions you will be using 

  • what checks will be carried out, and how often will they be carried out, to ensure the controls remain effective 

You should:

  • ensure that the release of water spray is properly controlled 

  • avoid water temperatures and conditions that favour the growth of legionella and other micro-organisms 

  • ensure water cannot stagnate anywhere in the system by keeping pipe lengths as short as possible or removing redundant pipework 

  • avoid materials that encourage the growth of legionella (The Water Fittings & Materials Directory references fittings, materials, and appliances approved for use on the UK Water Supply System by the Water Regulations Advisory Scheme)

  • keep the system and the water in it clean

  • treat water to either control the growth of legionella (and other microorganisms) or limit their ability to grow

  • monitor any control measures applied

  • keep records of these and other actions taken, such as maintenance or repair work 


Keeping records 

If you have five or more employees you have to record any significant findings, including those  identified as being particularly at risk and the steps taken to prevent or control risks.  If you have less than five employees, you do not need to write anything down, although it is useful to keep a written record of what you have done.

Records should include details of the:

  1. person or persons responsible for conducting the risk assessment, managing, and implementing the written scheme

  2. significant findings of the risk assessment

  3. written control scheme and details of its implementation

  4. details of the state of operation of the system, ie in use/not in use

  5. results of any monitoring inspection, test or check carried out, and the dates  


These records should be retained throughout the period for which they remain current and for at least two years after that period. Records kept in accordance with (e) should be retained for at least five years. 


Temperature probes are an important instrument for taking water temperatures and completing temperature checks for Legionella compliance requirements. When undertaking the various Legionella preventative tasks, a calibrated temperature probe is required. The probe which is used for taking temperatures from the water and pipework itself will form part of your record keeping and help you identify areas of risk.

Legionella thrives in temperatures between 25°C & 45°C. Cold water temperatures should reach below 20°C within 2 minutes of running the water and above 50°C within 1 minute (unless controlled by a Thermostatic mixing valve - TMV's should reach a temperature of between 38°C and 45°C) . 

The temperature probe should be calibrated every year and issued with a certificate of calibration.

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