HSE asked HSL to gather supporting evidence as to whether or not water miscible MWFs pose a Legionella infection risk and whether a Legionella risk assessment and appropriate actions are necessary. Three short studies were undertaken with the aim of determining a) whether free living Legionella survive in different types of MWF, b) whether amoebae, that act as hosts for the replication of Legionella, survive in different types of MWF and c) whether a greater concentration of Legionella cells can be detected in samples of used water-miscible MWFs compared to samples of potable mains water used in their preparation. In summary, the findings reported here suggest that neither free-living Legionella nor amoebae proliferate in water miscible MWFs.
It can therefore be concluded that if premises manage bacterial contamination of MWF systems in accordance with COSHH Essentials MW5 - Managing sumps and bacterial contamination and the guidance on HSE's Metalworking Fluids - bacterial contamination web pages, then they will be compliant with L8 (HSE, 2002) in respect to the management of these cold water systems. If microbial colonisation is kept to a minimum in MWF systems, a separate Legionella Risk Assessment is not normally necessary.
This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.
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