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Legionella - a Timely Reminder

28 March 2014 | Updated 01 January 1970
Legionella bacteria can be living in your water supply in fact anywhere in your building where water risk assessment legionella water collects. It causes Legionellosis, a pneumonia like illness, the most well known form is commonly known as Legionnaires' Disease.

Legionnaires’ disease is potentially fatal and everyone is susceptible to infection. However, some people are at higher risk, including:

  • People over 45 years of age
  • Smokers and heavy drinkers
  • People suffering from chronic respiratory or kidney disease
  • Anyone with an impaired immune system such as the elderly
Common bacteria

The bacteria are common in water systems, such as rivers and lakes but rarely in such concentrated quantities for people to catch Legionnaires' Disease. This normally occurs when Legionella is found in purpose built water systems, such as those within your building.  This is why it's essential to ensure your Legionella water risk assessment is up to date.

There are a couple of factors that need to be ideal for people to be infected by the Legionella bacteria.  They are:

  • The water the bacteria lives in, needs to be between 20 - 45 degrees C
  • The infected water needs to be free floating in vapor form so it can be inhaled. i.e. water droplets from a cooling tower or aerosol etc

There needs to be a source of food in the water supply to sustain the bacteria (sludge or scale within the system)

If these factors exist then the likelihood is you have Legionella bacteria lurking in your building and you, as the building operators, are responsible for identifying the risks to both the staff that work at the site and the visitors to the site.

Here are the top 5 areas where Legionella could be lurking. It is vital that you have an up to date risk assessment for each of these areas.


Legionella in cooling towers

Your cooling system may consist of a cooling tower, evaporative condenser or other cooling element. Legionella bacteria can reside in these along with the re-circulating pipe work, the heat exchanger, pumps and ancillary items such as supply tanks and pre-treatment equipment.

If your building contains any of the cooling systems mentioned above then you should be taking steps to identify the risks with a water risk assessment.  More information can be found on the HSE webiste.


Legionella in storage tanks

It's important to consider the amount of water you have on storage at any one point. Try and keep this to a minimum.  If you are using a number of water storage tanks then you should ensure that these are linked together to provide a continuous flow through the system thus avoiding stagnation in any one tank.If you are using one main tank to store your water then ensuring the inlet and outlet openings are on opposite sides will minimise water pockets within the tank that can stagnated and become infected due to insufficient flow around the tank.

If you refer back to the ideal conditions for Legionella then you'll note that keeping your stored water below 20 degrees C will minimise the risk of Legionella being able to thrive.  Along with this, keeping the equipment clean and free from scale and sludge will deprive any bacteria from a food source.


Legionella in cold water outlets

With water needing to be above 20 degrees C for Legionella to develop, you might think your cold water outlets are immune to the build-up of bacteria, far from it.  By the nature of these outlets (showers, taps etc) water flow can be turned off.  This means that water left in the system, at the point of exit or in the pipes can slowly increase in temperature over time.  If you have your cold pipes running too close to your hot water pipes then you will see an increase in temperature in the cold water system due to heat transfer.

Keeping a regular eye on the outlet temperature should be a regular part of your water risk assessment.


Legionella in hot water outlets and systems

Legionella bacteria can thrive in water temperatures of up to 45 degrees C.  The issue with Legionella's tolerance to a wide temperature range, is that as a building operator, you have to ensure the risk of scalding from these systems is minimised and to do this you need to keep water coming out of a hot water outlet to under 44 degrees C.  This makes hot water outlets in public areas a major risk for Legionella.

To minimise the risks in these areas keep any source of nutrients such as scale and sludge build up on the tap nozzle to a minimum.  Ensure these systems are included on your water risk assessment.


Legionella in 'other' water systems

In any building there are a number of other water systems that could pose a risk as a potential source for Legionella bacteria.  These include; humidifiers, emergency showers, eye wash sprays, indoor ornamental fountains, drinking fountains, aqueous tunnel washers etc.


Click here to obtain your free Legionella Checklist

Article written by Mark Lye | Published 28 March 2014


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