Controlling Exposure to MWF and Ensuring Ill Health is Avoided

Controlling Exposure to MWF and Ensuring Ill Health is Avoided

By Mary Cameron

The Health and Safety Executive (HSE) has recently written to fabricated metal businesses across Great Britain to check that they are managing the risks of metalworking fluids. They have announced upcoming inspections of fabricated metal businesses, between May and September 2021, to ensure duty holders know the risks, plan their work and have adequate control measures in place to protect workers’ health.

Inspectors will be checking that businesses are compliant with the guidance to manage the risk of respiratory diseases. Such guidance is available through the HSE’s COSHH essentials for machining with metalworking fluids (which have been recently updated), the UKLA/HSE good practice guide for safe handling and disposal of metalworking fluids, HSE’s INDG365 and HSE’s Operational Guidance OG-00109. These resources provide tools to help businesses ensure they have the necessary measures in place to protect worker’s health.

Before the HSE inspections begin, businesses should ensure they are prepared. Accessing the right guidance and resources to help manage the risks is essential.

Here at EEUK Group, we can help. Our occupational hygienists are experienced and knowledgeable in managing the risks of machining with metalworking fluids. We take a direct approach to managing the risk; focus on the source of the problem (fluid quality management) and evaluate the controls via qualitative analysis (application of a direct reading aerosol monitor (DRAM) alongside a dust lamp and fake smoke generator). The DRAM is a hand-held aerosol monitor which displays real-time results. Airborne sampling may also form part of the assessment strategy. Although airborne sampling should be decided with caution as this may not provide reliable results in many cases (discussion below).

EEUK Group’s occupational hygiene technical manager, Mary Cameron BSc LFOH CertOH, has considered this approach carefully and created a table (accompanying this article) which lists the pros and cons to each metalworking fluid exposure assessment / evaluation method.


  • gravimetric active sampling of mineral oil-based metalworking fluids, marker-element active sampling of water-mix metalworking fluids,
  • FTIR analysis of petroleum distillate-based metalworking fluids,
  • GCMS analysis to determine Total Petroleum Hydrocarbon content of the metalworking fluids,
  • airborne microbial and/or endotoxin sampling, application of a DRAM with dust lamp (Tyndall beam) and fake smoke generator to detect control failings (such as leaks of the enclosure or poor extraction of the airborne contaminant cloud),
  • and auditing of the fluid management system e.g., assess if the metalworking fluid concentration is being maintained correctly, checks on the temperature, pH, appearance and odour of the fluid, water source quality checks, signs of contamination (tramp oil, metal fines), maintained circulation to prevent stagnation, and regular dip slides testing to check microbial growth.

The health risks associated with metalworking fluids are thought to be from a microbial origin i.e., the presence of bacteria and endotoxins. The focus should be on the root of this exposure, which is a poorly implemented fluid management system and inadequate controls. A poorly managed system will likely lead to increased microbial growth. Inhaling this contaminated metalworking fluid mist may cause lung diseases such as hypersensitivity pneumonitis and occupational asthma.

Skin disease (dermatitis- contact and allergic) may also occur if the skin is in regular contact with the poorly managed metalworking fluid e.g., tramp oil, swarf and metal fines contamination or substances in the concentrate, neat oils, biocides, and additives.

The health risks can be managed should the composition of the fluids be prevented from deteriorating whilst in-use (fluid contamination and conditions which favour microbial growth). The fluid management system audit should also be accompanied with an assessment of the control measures. The exposure controls in place should include means to reduce the mist released and to avoid direct contact with the fluid.

Mist control measures may include using enclosures (e.g., retrofitting roof panels), applying the fluid at the lowest possible pressure, personal decontamination and skin care, good housekeeping, fluid management, incorporated mist filtration extraction units, good working procedures e.g., avoiding the use of airlines to blow down the components and employing instead vacuum guns, absorbent materials, spindle mounted fans or automatic compressed air hoses within the CNC enclosure. As well as programmable delays in opening CNC enclosures (via access door interlocks) until the mist clearance time has elapsed.

It is crucial that information, instruction, and training for the workers is provided in relation to the risks and controls. A monitoring system for the effectiveness of these controls is also essential as this will trigger prompt remedial actions when required. A health surveillance programme may be needed if there is a reasonable likelihood that asthma may develop due to regularly inhaling MWF mists.

The COSHH regulations state ‘monitoring is not appropriate if suitable techniques for sampling, analysis, and quantification do not exist, or cannot be devised or if the employee is able to demonstrate that an alternative method of evaluation has been used to ensure that exposure is adequately controlled’.

As we are dealing with a mist with MWFs, this can be visualised using a dust lamp. A DRAM can also assess relative changes to the concentration of the MWF mist by providing real-time readings of aerosol levels. And thus, the DRAM, alongside the dust lamp, can quickly identify failures in the control systems.

For example; a leak along the machine’s enclosure allowing the mist to escape and spread, poor extraction provided by the local exhaust ventilation system which does not fully control the contaminant cloud, before and after measurements showing the effectiveness of an LEV filter replacement, an inadequate clearance time of the enclosure post-milling cycle leading to the operative opening the machine doors too soon and releasing the lingering mist within, the use of compressed air tools causing a peak in mist levels, unnecessarily high machinery speeds causing excessive mist generation. A Tyndall beam (dust lamp) as well as a fake smoke generator are important accompanying tools to this control evaluation via a DRAM. The dust lamp highlights aerosol particles not seen with the naked eye. And the generated fake smoke allows visualisation of air flow movement within or around the machinery. This evaluation can help inform decisions regarding where to focus investments to improve exposure control measures.

There may be cases still where active airborne sampling is requested. For example, should further data be needed to make an informed decision regarding the likely exposure levels (should it not have been practicable to gather sufficient information during the fluid management audit or qualitative analysis).

EEUK Group can provide this sampling should it be deemed necessary but cautions that these sampling methods have notable limitations.

Gravimetric active sampling of mineral oil-based metalworking fluids based on MDHS 84/2 is only suitable for high viscosity oils. Otherwise, the volatile fraction sampled onto the filter may be lost and thus the gravimetric analysis may underestimate the sampled airborne aerosol concentration.

Marker-element active sampling of water-mix metalworking fluids based on MDHS 95/3 is only suitable when the machine sump fluid contains an element present at a high enough concentration to facilitate its use as a marker and when said marker is unlikely to come from a source other than the water / metalworking fluid concentrate. The marker may be boron, potassium or sodium. Although typically boron. However, following the recent classification of boric acid as a substance of very high concern, lubricant manufacturers have sought alternatives and developed miscible MWFs without or with reduced content of boric acid. And so, boron may not be present or in high enough concentration to be used as a marker. Further research is underway re reliable quantitative methods.

A UK workplace exposure limit is not available for metalworking fluids. Reason being, outbreaks of ill-health have occurred across the world in machining plants using water-mix MWFs despite apparent compliance with national exposure or guidance limits designed to protect worker health.

In 2005, HSE decided to withdraw all guidance values relating to MWF as their value in protecting worker health was limited and were providing a false sense of protection. Guidance limits are however still available from other sources e.g., a NIOSH REL based on total particulate mass (0.5 mg.m-3) can be applied but with caution. This is not a health-based limit and may still result in cases of lung disease below this level.

Similarly, a UK workplace exposure limit is not available for water-mix metalworking fluids. The withdrawn guidance value of 1.0 mg.m-3 can be applied but again with caution. This also is not a health-based limit and was previously defined as a ‘good practice’ control level. Although outbreaks of lung disease have occurred under this level and so it is not a safe limit.

In all, active sampling results will likely tell you that the source of the contaminant cloud is from the poorly controlled metal turning machinery, which we likely would have already known from careful site observations and a qualitative evaluation. It should be clearly understood that the airborne sampling results should not be solely relied upon when deciding where to focus control improvements. No matter the sampling result, it is vital that the principles of good practice for the control of exposure to substances hazardous to health be applied.

The withdrawal of metalworking fluids-related guidance limits left the UK without a benchmark to demonstrate adequate control of mist. The lack of a health-based exposure limit to base the sampling results against is a considerable drawback to a quantitative sampling approach.

The sampling methods themselves also having many drawbacks, as discussed, and can give ‘fuzzy numbers’ to work with. This quantitative approach may also take attention away from what is paramount; controlling exposure by measures that are proportionate to the health risk (as per COSHH Schedule 2A part c).

Due to the severity of the diseases that metalworking fluid may cause, a high level of control is warranted. This broadly equates to ALARP (as low a level as is reasonably practicable). And so, the focus should be given to achieving ALARP via properly managing the fluid quality, controlling the mist generation at source and preventing direct contact with the fluids.

EEUK Group advise that the most constructive approach to evaluating the risks to metalworking fluids exposure is auditing the fluid management system along with a qualitative analysis of the exposure controls in place.

Quantitative sampling can provide the employer with some evidence about the adequacy of their control measures, but this must be complemented with observations made during the qualitative analysis and the achievement of adequate control decided in line with the requirement of ALARP.

Mary Cameron BSc LFOH CertOH

OH Technical Manager at EEUK Group