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HSE announces legionella bacteria guidance update

16 April 2024

THE HEALTH & Safety Executive (HSE) has updated its technical guidance publication 'The control of legionella bacteria in evaporative cooling systems' (HSG274: Part 1).

According to the HSE, the guidance for managing the legionella risk presented by these systems has been improved in several areas.
These changes include further information on DPD No 1 testing methodology, and the effect that cooling water pH has on the efficacy of halogen-based biocides such as chlorine and bromine.

Many organisations rely on this test to ensure correct dosing of their systems. The pH correction of free-halogen test results is a vital part in ensuring that you have sufficient biocide in your system to prevent the growth of legionella.
The second edition of HSG274 has been reviewed and updated in Part 1 only – 'The control of Legionella bacteria in evaporative cooling systems'.
A simple assessment can reduce the risk of legionella. Legionnaires' disease is a potentially fatal form of lung infection. It is normally contracted by inhaling small droplets of water (aerosols), suspended in the air, containing the bacteria.
If you are an employer, or someone in control of premises, you must understand the health risks associated with legionella and take the right precautions to reduce the risks of exposure to legionella: hot water storage cylinders (calorifiers) should store water at 60°C or higher; hot water should be distributed at 50°C or higher (thermostatic mixer valves need to be fitted as close as possible to outlets, where a scald risk is identified); and cold water should be stored and distributed below 20°C.
The bacteria begin to die in temperatures above 50°C and cannot survive above 60°C
The guidance is available in the HSE's downloadable publication Legionnaires' disease - The Control of Legionella bacteria in water systems.