Our technical guidance publication 'The control of legionella bacteria in evaporative cooling systems' (HSG274: Part 1), has been updated. The guidance for managing the legionella risk presented by evaporative cooling systems has been improved in several areas. These changes include: further information on DPD No 1 testing methodology 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. Note that the second edition of HSG274 has been reviewed and updated in Part 1 only 'The control of Legionella bacteria in evaporative cooling systems'. Download the updated publication from our website 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, such as a landlord, 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 60C or higher hot water should be distributed at 50C or higher (thermostatic mixer valves need to be fitted as close as possible to outlets, where a scald risk is identified) cold water should be stored and distributed below 20C The bacteria begin to die in temperatures above 50C and cannot survive above 60C Get further advice HSE's website offers: guidance in our downloadable publication Legionnaires' disease - The Control of Legionella bacteria in water systems (.pdf) practical advice and guidance to help you understand the risk from legionella and legionnaires' disease If youre looking for specific advice related to tasks or processes in your industry, check out the direct advice sheets listed by industry. The sheets offer practical guidance for managing hazardous substances. Find your industry direct advice sheet | 