Legionnaires' disease is the most serious disease of a group of diseases collectively known as legionellosis. Legionnaires' disease is a pneumonia that mainly affects susceptible people such as the elderly, the young, the immunocompromised, heavy smokers and those that are already ill, and in certain cases Legionnaires' disease can be fatal.
The Legionella bacteria can be found in many places, especially in water sources such as rivers, streams and ponds, and in many re-circulating water systems such as water cooling towers, air conditioning systems and whirlpool spas. Outbreaks of Legionnaires' disease have occurred in or near large building complexes such as hotels, hospitals, offices and factories. There is no evidence that water systems in domestic homes present any risk.
Infection is attributed to people inhaling Legionella, present in water droplets, that are small enough to penetrate deeply into the lung. However for this to happen a series of events needs to occur and this includes: -
- Conditions present that are suitable for the multiplication of the organism, i.e. water temperature in the range: 20oC - 45oC.
- The presence of sludge, scale, rust, algae and organic matter to provide nutrient for the bacteria.
- A means of creating breathable droplets, i.e. via water-cooling towers. Cooling towers are considered a particular hazard because they generate large amounts of fine droplets, usually at rooftop level where there is potential for air currents to carry the droplets over a relatively large area.
- Inhalation of the contaminated droplets by a person or people.
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The risk of legionellosis can be reduced by the proper implementation of a COSHH assessment that will identify potential hazardous plant and equipment and appropriate control measures. The risk can also be reduced by:
- Designing cisterns and pipework so that water is not allowed to stand undisturbed for long periods.
- Cisterns should be well covered to prevent entry of dirt, debris and vermin, and periodically inspected, cleaned and disinfected.
- Water temperatures between 20oC - 45oC should be avoided by insulation of cold water tanks in warm spaces and by storing hot water at 60oC and circulating at 50oC.
- Only water system fittings and materials which comply with water authority bye-laws should be used, as certain materials such as leather and some rubbers support the growth of bacteria.
- Cooling towers and their associated water systems need to be well designed, maintained and operated. It is especially important that drift eliminators are fitted to prevent the escape of fine water droplets.
- Systems should be cleaned and disinfected at least every six months.
- Water should be treated to prevent scale, corrosion and microbial growth.
- Consideration should be given, when practicable, to replacing cooling towers with dry cooling systems.
In situations where your COSHH assessment has identified that you may have a potential problem in your premises you should appoint an appropriate person to manage, organise and supervise the precautions that you decide are necessary to minimise the risk from legionellosis.
There are legal requirements under the Health and Safety at Work, etc. Act 1974 that require you to protect the health and safety of your employees, and of other people associated with your business.
There is also a legal duty for all people in control of premises that contain wet cooling towers and/or evaporating condensers to notify their local authority's Environmental Health Department that they have this equipment. Such notification will help the relevant people to act quickly in the event of an outbreak.
Action must be taken quickly if an outbreak occurs and this should include:
- Notifying the local authority's Environmental Health Department, who will contact other specialists to react quickly to the situation
- Identifying the source
- Identifying people likely to be affected
- Ensuring that the contaminated water is treated as quickly as possible
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