Legionella Risk Assessment: Prevention

Which systems present the greatest risk against legionella?

Cooling towers, evaporative condensers and hot and cold water systems have been associated with outbreaks. Other potential sources where precautions might be needed include humidifiers and spa baths. If you decide that the risk is insignificant, your assessment could be a simple documentation of the system. You need take no further action other than to review the assessment periodically in case anything changes in your system.

 

Preventing or controlling the risk of legionella

If a risk is identified which cannot be prevented, employers must introduce proper controls. Risks from legionella in water systems can be controlled but careful planning, a successful management policy, competent staff and attention to proper control strategies are all essential.

 

Employers should consider whether they can prevent the risk of legionella in the first place by looking at the type of water system they need. For example, is it possible to replace a wet cooling tower with a dry air cooled system?

 

Employer need to prepare a written scheme which sets out how you intend to control the risk from legionella. The scheme should describe:

 

• If there is an up-to-date plan or schematic diagrams which are sufficient
• 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 will be used or are in place
• The checks that will be carried out on the control scheme and how often these checks will be carried out.
  

The key point is to design, maintain and operate your water services under conditions which prevent or control the growth and multiplication of legionella.

 

Employers should:

 

• Ensure that the release of water spray is properly controlled
• Avoid water temperatures and conditions that favour the growth of legionella and other microorganisms
• Ensure water cannot stagnate anywhere in the system by keeping unused pipe lengths as short as possible or by removing redundant pipework
• Avoid materials that encourage the growth of legionella
• Keep the system and the water in it clean
• Treat water to either kill legionella (and other micro-organisms) or limit their ability to grow.
  

Keeping the water in a cooling tower system clean will not only control legionella, but also lead to other advantages. By reducing scale and fouling, you are also ensuring that the cooling process is operating efficiently. If appropriate measures are not taken then reduction in the effectiveness of biocide treatment and fouling can lead to loss of plant performance.

 

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