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Assessing the risks of legionella

legionellaA recent case in the news highlights the importance of ensuring you are compliant with legionella legislation and are aware of legionella risk factors.

The story details how a hotel operator was fined £54,000 following a legionella outbreak at its premises. 65 people fell ill with 18 confirmed to have contracted Pontiac Fever following the incident.

The origin of the outbreak was found to be from a spa pool in the hotel which had not been correctly maintained following the departure of a senior member of staff the pool had not been fully drained or disinfected for over two months and the recommended daily maintenance of the filters had not been carried out. When the chlorine levels became dangerously low following the failure of the chlorine injectors the pool was closed.

However despite being out of use, the pool was left switched on in an attempt to prevent the water from stagnating. In doing this the water was kept within the ideal temperature zone for legionella and also agitated producing droplets and allowing the bacteria to become airborne.

This incident highlights the importance of legionella awareness and knowledge of how to prevent and manage an outbreak. We have highlighted a few of the most common questions on legionella and the importance of assessing the risks from legionella within your water systems.

What is Legionella?

Legionellosis is the collective name given to the pneumonia-like illness caused by legionella bacteria. This includes the most serious legionnaires’ disease, as well as the similar but less serious conditions of Pontiac fever and Lochgoilhead fever. Legionnaires’ disease is a potentially fatal form of pneumonia caused by legionella bacteria which naturally occur in water sources and can often then contaminate man made water systems.

The symptoms of Legionella include:

  • High Fever
  • Chills
  • Headaches
  • Tiredness
  • Muscle pain/aches
  • Dry cough and difficulty with breathing

Developed Symptoms include:

  • Vomiting
  • Diarrhoea
  • Confusion & deliration

Legionella risk factors

Given the correct conditions any water system can potentially harbour and grow legionella bacteria. There are potential risks of a legionella outbreak if your water systems provide conditions which will encourage the bacteria to multiply, these include:

  • If the temperature of the water within the system is between 20-45°C
  • Water is stagnant or re-circulated within the system
  • If there is build up of rust, sludge, scale, organic matter and biofilms
  • If water droplets are produced, and if they can be dispersed over a wide area, such as showers and mist sprays
  • If any of your employees, residents, visitors etc. are more susceptible to infection due to age, illness, a weakened immune system and whether they could be exposed to any contaminated water droplets.

Do you require a legionella risk assessment?

If you own or manage a building which has water systems or plant, yes you are required by law to assess the risks of legionella.

What is the purpose of a water risk assessment?

Carrying out a Water Risk Assessment will help you to identify potential hazards within your water systems and recommend actions to reduce the risk of legionella outbreaks. It involves a physical survey by a competent person of all water related plant and storage systems.

What should it include?

Your risk assessment should include:

  • Management responsibilities, including the name of competent person and a description of your system;
  • Potential sources of risk;
  • Any measures in place to control risks;
  • Monitoring, inspection and maintenance procedures;
  • Records of the monitoring results, inspections and checks carried out;
  • Arrangements to review the risk assessment regularly

If no risks are found or if you decide that the risks are insignificant and are being properly managed, your assessment is complete. You may not need to take any further action at this stage but you should review the assessment regularly in case anything changes in your system.

How often do you need a risk assessment?

The findings of the assessment should be recorded and reviewed whenever there is a reason to suspect that it is no longer valid such as when:

  • There are changes to the water system or its use, this could be due to changes in occupancy.
  • Changes to the use of the buildings in which the water system is installed
  • The availability of new information regarding risks or control measures
  • Checks including positive samples indicate that the control measures are no longer effective
  • A case of legionnaire’s disease/leginellosis is associated with the systems.

For medium or high risk systems or properties where there are a number of issues that require action, or where management controls are lacking, MetroSRM would recommend that a review is carried out annually.

Once the risk assessment is complete a written scheme needs to be developed and implemented which will prevent or control the likelihood of a legionella outbreak occurring. The appointed responsible person needs to ensure the scheme is implemented and managed successfully. This task should be carried out by a competent person and can be delegated to an external contractor.

If you need any help or have any questions regarding your legionella risks, why not call our team of water safety specialists on 0845 058 9999.


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Metro Safety
Metro House
79-80 Blackfriars Road
London SE1 8HA
0845 058 9999

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