HSE update on Legionella guidance for evaporative cooling systems

Greg Davies 2022

Greg Davies
Director of Market Development, Assurity Consulting
4th April 2024

The 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.”

With many dutyholders who manage evaporative cooling systems (cooling towers and evaporative condensers) using halogen-based biocides (e.g. bromine and chlorine), both the testing method itself and the need to correct for the cooling water pH, are fundamental to an accurate dosing regime and so control of the system.

It would be hoped that for the vast majority of those managing evaporative cooling systems, that the test method and pH correction are already part of their control regime. Even so, with the changes, a review of the process to make sure it is meeting the guidance would be advisable. We will of course be working with our customers to highlight the changes. Here is a link to the updated guidance:

Legionnaires' disease - Technical guidance (hse.gov.uk)

 It should also be noted that these changes only affect Part 1 of the technical guidance, Parts 2 (hot and cold water systems) and Part 3 (other water systems) remain as previous.