How effective is your Legionella Risk Assessment?

Legionnaires’ disease is a pneumonia type of infection that affects the lungs and the lower respiratory tract. Legionnaires’ disease is caused by the inhalation of airborne droplets, or aerosols, containing the bacterium Legionella pneumophila. The infection is fatal in 10-12% of cases.

Legionella occurs naturally, and is widespread in the environment. The bacteria may colonise man-made systems or water services where favourable conditions are present.

Water temperatures within the range of 20°C - 50°C are most likely to support the growth of the bacteria, and the optimum temperature for proliferation is 37°C. Legionella may survive at temperatures below 20°C in a dormant state.

The presence of sediment, scale, organic materials, bacteria, amoebae and algae can all provide nutrients and protection for Legionella, offering a stable environment for survival and multiplication.

Biofilm formation within a water system can provide favourable conditions for growth and they can protect the organism from concentrations of biocides that would otherwise kill or inhibit Legionella.

Legionnaires’ disease is most commonly associated with contamination of hot and cold water systems within buildings, cooling towers, humidifiers and spa baths. It is important that all systems susceptible to colonisation by Legionella, and which incorporate a potential means for creating aerosols, should be identified and the risk they present should be assessed.

A Legionella risk assessment should be carried out by a competent person who has the necessary skills, experience and qualification. If necessary the duty holder may appoint an external consultant to assist with the assessment. The process involves a full inspection of the site water system, from the point it enters the property boundary to the point at which the user comes into contact with water. A suitable and sufficient Legionella risk assessment should include all areas where water is used or stored, to determine the level of risk from Legionella.

The Legionella risk assessment should satisfy the requirements of the Health & Safety Commission’s approved code of practice 2001 (L8): ‘Legionnaires’ disease – the control of legionella bacteria in water systems’, and pays particular attention to the following factors:

• Water temperature

• Water stagnation

• Potential for aerosol formation

• Heat gain / loss potential

• Condition of the water

• Condition of the water service and the water system as a whole

• The susceptibility and population density of exposed persons

A Legionella risk assessment should be reviewed regularly and whenever there is reason to believe the original assessment may no longer be valid.

The findings of the Legionella risk assessment should be taken into consideration when producing a scheme to prevent or control the risks so it is essential that duty holders ensure that their assessment is comprehensive and accurate in order to reduce the likelihood of Legionnaires’ disease.