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Legionella Control (HSE)
Temperature control is the primary method used to control the risk from Legionella.
Water services must be managed and controlled at suitable temperatures that will prevent Legionella Proliferation (growth) such as:
- Hot water storage cylinders (calorifiers) should store water at 60°C or higher
- Hot water should be distributed at 50°C or higher
- Cold water should be stored and distributed below 20°C.
- Thermostatic mixer valves (TMV) need to be fitted within 1.5 metres of the outlet it supplies.
Your Legionella Control (HSE) manager should frequently inspect, monitor and maintain the water system, in accordance with the site risk assessment.
Sentinel outlets (nearest and furthest to stored hot and/or cold water) should be identified so that monthly checks of distribution temperatures can be carried out. Stored hot water temperatures should also be checked and reviewed every month and stored cold water tank temperatures at least every six months.
As stagnant water provide Legionella bacteria an ideal environment for growth, dead legs/dead ends in pipe-work should be removed. Infrequently used outlets, (especially aerosol generating outlets such as showerheads) should be flushed on a weekly basis. All outlets that generate a spray (showers and spray taps) should be cleaned and descaled on a quarterly basis. Cold-water storage tanks should be cleaned periodically and all water should be drained from hot water cylinders to check for debris or corrosion.
Water sample analysis can be used as an additional control method for systems that are presenting temperatures out with the control parameters.
How do I carry out a Legionella risk assessment?
The purpose of carrying out a risk assessment is to identify and assess any risks in your water system. The responsible person should understand your water systems and any associated equipment, in order to conclude whether the system is likely to create a risk from exposure to legionella, and should be able to identify whether:
- water is stored or re-circulated as part of your system
- the water temperature in some or all parts of the system is between 20–45 °C
- there are sources of nutrients such as rust, sludge, scale and organic matters
- conditions are present to encourage bacteria to multiply
- it is possible for water droplets to be produced and, if so, whether they could be dispersed over a wide area, eg showers and aerosols from cooling towers
- it is likely that any of your employees, residents, visitors etc are more susceptible to infection due to age, illness, a weakened immune system etc and whether they could be exposed to any contaminated water droplets
Your risk assessment should include:
- management responsibilities, including the name of competent person and a description of your system;
- potential sources of risk;
- any controls in place to control risks;
- monitoring, inspection and maintenance procedures;
- records of the monitoring results, inspections and checks carried out;
- arrangements to review the risk assessment regularly
If you decide that the risks are insignificant, your assessment is complete. You may not need take any further action at this stage but you should review the assessment regularly in case anything changes in your system.find out more