Are Metal Working Fluids a Legionella risk?

Before you read this post do you have an opinion as to whether cutting oils are a risk or not?

What do Legionella bacteria require to thrive? A warm environment, water (normally), organic material, biofilms, other bacteria, the right pH, iron, static areas. Well aren’t they all present in cutting oils? And it is well known that other bacteria thrive in cutting oils as they represent a dermatitis issue.

Well what is your answer? Yes or No?


Were you aware that several years ago (well 2012 actually) the Health & Safety Executive asked themselves the same question and as a result commissioned some research by their colleagues as to whether cutting oils are a risk or not. The resulting document was entitled: “Survival of Legionella pneumophila in metalworking fluids”

The key findings of the report were:

• Free living intra-amoebic grown Legionella pneumophila did not proliferate in three different types of water mix metal working fluid (MWF) products tested.

• >99.99% kill of L. pneumophila was observed within 4 hours when placed in these MWFs.

• Although the proportion of surviving amoebae was very low, it varied (in one fluid the loss of viability occurred more slowly). This may be attributed to the formulation of the different MWFs.

• Based on the use of a specific polymerase chain reaction (PCR) assay to detect Legionella species DNA, low levels were observed in 70 different samples (representing 18 different MWF products from 35 different manufacturing sites across the UK). These were below the proposed action level of > 1 x 10 genomic units / litre    5 (GU/L) for L. pneumophila in hot and cold water systems.

• Levels of Legionella species DNA in 25 different potable mains water samples (from different regions of the UK) were similarly low.

• This result suggests that levels of Legionella DNA in used MWF samples are comparable to drinking water supplies and that no proliferation of Legionella has occurred in these MWF samples.

• Based on the above data, the risk of Legionella infection from free flowing MWF is considered to be extremely low, but risks arising from the association of Legionella   with biofilm were not examined in this study. These risks need to be addressed by maintaining MWF systems in accordance with HSE guidance to keep levels of bacteria to a minimal level and to avoid the likelihood of biofilm formation.

• If biofilm is disturbed during deep cleaning work, potential exposure to Legionella   needs to be considered in the risk assessment.

So based on that has your view changed?

The conclusion of the report were:

…that if premises manage bacterial contamination of MWF systems in accordance with COSHH Essentials “Managing sumps and bacterial contamination” MW5 ( 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. It should be noted however that this conclusion could be influenced by other factors as outlined above, such as the presence of biofilm.

The survival of Legionella in water biofilms has been widely published (Green, 1993; Rodgers et al, 1994, Murga et al, 2001), as has the airborne spread of Legionella (Mathieu et al, 2006, Nguyen et al, 2006) but survival in MWF biofilms has not been reported.

It is recommended that:

1. The routine handling of water miscible MWFs is risk assessed and managed in  accordance with HSE’s guidance on bacterial contamination of MWFs. This will normally be sufficient to meet the requirements set out in L8 (HSE, 2002).

2. A separate risk assessment should be prepared where biofilm is to be disturbed, for  example during deep cleaning work which may increase the potential for aerosolisation of, and therefore airborne exposure to, organisms contained within biofilm.

So it looks like the answer is not clear cut as biofilms are more than likely to exist in metal working fluid systems so take note of the recommendation to comply with MW05.

But…this work was carried out before HSG 274 Part 3… but then that document does not mention Metal Working Fluids.

If you want to discuss the contents of the report, or indeed would like a copy then contact us on or phone on +44 (0)7958 124563


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