Legionella Control (HSE)

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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.

FAQ’s

How often should I test water for Legionella?

It depends on the system that you have and the outcome of your risk assessment. For open systems, such as cooling towers, evaporative condensers and spa pools etc, routine testing should be carried out at least quarterly. However, there may be circumstances were more frequent sampling may be required.

For hot and cold water systems, which are generally enclosed, i.e. not open to the elements and significant contamination in the same way as cooling towers, microbiological monitoring is not usually required. But there may be circumstances where testing for legionella is necessary eg where there is doubt about the efficacy of the control regime or where recommended temperatures or disinfection concentrations are not being consistently achieved . Further guidance is available in HSG274 Part 2

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