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Legionella: a quick guide

The airborne bacteria is something that everyone who works in building services should be aware of, whatever their position, as Tony Ellerker reminds us

Outbreaks of Legionnaires’ disease frequently bring the public’s attention to the role of air conditioning units in the spread of the Legionella bacteria. However, the association is one based on a common misconception.

There are no credible cases of Legionnaires’ clearly linked to air conditioning in the scientific literature, with studies showing that outbreaks are usually related to a building’s domestic hot water system.

In order for employers to be able to prevent outbreaks of Legionnaires’ in the workplace, the myths must be separated from the facts.

What is Legionnaires’ disease?

Legionnaires’ disease is an infection usually caused by a bacterium named Legionella pneumophila.

Symptoms of Legionnaires’ disease include:

  • Fevers, chills and a coughs;
  • Some patients have muscle aches, headache, tiredness and loss of appetite;
  • Chest-rays often show pneumonia.

How is it contracted?

The most commonly accepted reason for contracting Legionnaires disease is through inhalation of mists contaminated with Legionella bacteria.

 The conditions suited to the multiplication of the organism include:

  • Water temperatures in the range between 20 deg C to 45 deg C;
  • The presence of sludge, scale, rust, algae and organic matter to provide nutrients;
  • For infection to take place, there must then be a means of creating breathable droplets from the organisms and then contact with the droplets by a susceptible person. The disease cannot be passed from person to person.

Where can Legionella bacteria be found?

The bacteria can be found within:

  • Cooling towers;
  • Whirlpool spas;
  • Showers which are fed from a hot water storage tank;
  • Humidifiers.

Therefore, the bacteria is not found in conventional air conditioning systems because there is no water inside the system.  However, preventative steps still need to be taken in order to reduce the risk of outbreaks.

How to prevent Legionnaires’ disease

Legionella cannot be prevented from entering a water systems as it is so widespread in the environment. However, the risk of an outbreak can be reduced by taking simple preventative steps. Employers are responsible for taking reasonable steps to ensure the health and safety of their staff, and so need to take precautions in order to reduce the risks of outbreaks.

Risk assessments

Employers must carry out risk assessments, and be able to understand water systems and associated equipment such as pumps, heat exchangers, showers, and other constituent parts.

They should also identify whether they are likely to create a risk from exposure to legionella, and whether:

  • The water temperature in all or some parts of the system is between 20 deg C and 45 deg C;
  • Water is stored or re-circulated as part of the system;
  • There are sources of nutrients such as rust, sludge, scale, organic matter and biofilms.

Regular maintenance

Ensure that regular maintenance, cleaning and treatment of susceptible equipment is undertaken. Domestic hot water systems should be controlled to raise the water to over 60 deg C for a predetermined time, at regular intervals (daily for example).

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.  

Tony Ellerker is the director of Blakes M&E Building Services, which provides service, repair and installation of electrical and mechanical systems.

RAC’s sister publication H&V News is hosting its annual Combating Legionella conference on 29-30 September. More details at: combatinglegionella.hvnplus.co.uk

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