Metal Working Fluid (MWF)

Metalworking Fluids are neat oils or water-based fluids used during the machining and shaping of metals to provide lubrication and cooling. They are sometimes referred to as suds, coolants, slurry or soap.

Exposure to metalworking fluids can cause:

• irritation of the skin or dermatitis; and

• lung diseases, such as occupational asthma, occupational hypersensitivity pneumonitis, bronchitis, irritation of the upper respiratory tract and other breathing difficulties.

Metalworking fluids are mostly applied by continuous jet, spray or hand dispenser and can affect your health:

• if you inhale the mist generated during machining operations;

• through direct contact with unprotected skin, particularly hands, forearms and face;

• through cuts and other broken skin; and

• through the mouth if you eat, drink or smoke in work areas, or from poor personal hygiene, eg not washing hands before eating.

HSE Inspections:

THE HEALTH and Safety Executive (HSE) has been carrying out inspections since September 2023 to check staff are safe when working with metalworking fluids or coolants. Failings were identified at more than half of those checked.

Inspectors are focusing on how employers ensure workers are protected from exposure to fluid or mist generated by computer numerical control (CNC) machines and that regular health checks are in place. There are three areas where manufacturing companies, particularly smaller companies, commonly fall down on compliance: 

1. Not having local exhaust ventilation 

2. Not completing regular fluid quality checks 

3. Failing to provide regular health checks for lung and skin conditions. 

So What do you need to do as an Employer?

• Carry out a suitable and sufficient risk assessment. This must be documented if you have 5 or more employees

• Maintain fluid quality and control bacterial contamination of fluids;

• Minimise skin exposure to fluids,

• Prevent or control airborne mists and

• where there is exposure to fluid or mist, carry out health surveillance.

To achieve the necessary control and risk reduction, among other actions, you will need to:

• check and maintain exposure control measures, such as enclosures and local exhaust ventilation;

• check levels of bacterial contamination using dip slides, or other means of measuring the level of bacterial activity, in both metalworking and associated fluids eg in washing machines, and act on the readings obtained in line with your risk assessment;

• ensure that, as a minimum, a responsible person carries out the required health surveillance.

• refer anyone affected by exposure to a competent occupational health professional;

• take prompt action after any diagnosis of ill health to identify the likely cause and ensure it is prevented or adequately controlled; and

• keep workers informed of all findings.

MWF in CNC Machines

• Apply MWF at the lowest possible pressure and flow volume consistent with adequate lubrication, cooling and swarf removal.

• Apply MWF at the point where the tool and workpiece make contact to minimise mist generation from contact with other rotating parts.

• Stop MWF delivery when not machining. You will still need to maintain fluid circulation to prevent stagnation (see MW5 Managing fluid quality). LEV Design and Use

• Enclose machines as much as possible eg. retrofitting roof panels.

• Provide local exhaust ventilation (LEV) to the enclosure. This can either be as a standalone unit or a centralised system linking two or more machines.

• Design considerations should include the volume flow rate, location of the extraction point(s), volume and dimensions of the enclosure and the level of mist generated from machining. These will affect the time taken for the mist to be extracted. See G406 New and existing engineering control systems

• Discharge extracted air to a safe place outside the building, away from doors, windows and air inlets. 

• If the extracted air is recirculated back into the workshop, ensure a suitable high efficiency air cleaning device is in place. 

• Provide an easy way of checking the LEV is working, eg. airflow indicator or equivalent.

• Observe a time delay between the machine stopping and opening the enclosure doors, to ensure when the operator opens the doors, no mist is present in their breathing zone (the area within 20-30 cm of the nose and mouth).

• The time delay can be established by filling the enclosure with smoke or using a dust lamp to observe fine mist. You can implement the time delay by including it in the machine programme or using a timer. 

• You should consider using alternative methods to clean away excess fluid and swarf/chips from machined parts during machining eg. vacuum guns, absorbent materials, low pressure coolant guns, spindle mounted fans or automatic compressed air hoses (operated with CNC enclosure doors shut).  

• Where there is no practical alternative: –Reduce the exit pressure of the compressed air to as low a level  as practicable (as a guide 30psi/2.1bar is effective at cleaning). –Different nozzle designs allow guns to be operated at a lower pressure. This will reduce risks from MWF, ejected swarf and noise. –Blow down components inside the CNC machine with the  LEV operating. –Consider using compressed air guns with longer lances (eg. 30 cm)

• Finished components can be cleaned in industrial washing/degreasing machines 

• Suitable swarf vacuums should be used to remove wet swarf/chips from machine surfaces.

Testing:

Test kits can be found sold online by various companies. Search for: microbiological + dipslides

Take dipslides once a week. To reduce this frequency of testing you first need to demonstrate that your fluid quality management is effective, eg dipslide, fluid concentration and pH test records.

A dip slide consists of a plastic carrier coated with a sterile culture medium, which is dipped into the liquid to be tested. It is then incubated to allow microbial growth and the resulting colonies are estimated by reference to a chart to indicate the level of bacterial contamination. Results are expressed in terms of colony-forming units per millilitre (CFU/ml) of fluid.

The following values indicate what can be regarded as good, reasonable and poor standards of fluid management, and what action should be taken. Monitoring should be used to confirm your standard of control, as well as indicating increased levels of bacteria at an early stage.

• <104 CFU/ml Good control. Bacteria are being maintained at low levels. Regular checks and actions to maintain the fluid quality should continue.

• ≥104 to <106 CFU/ml Reasonable control. Review and take action to check the quality of the metalworking fluid and adjust fluid parameters to those recommended by the supplier. If bacterial growth continues despite these adjustments, add biocide at the dose recommended by your supplier.

• ≥106 CFU/ml Poor control. Immediate action should be taken in line with the risk assessment. Normally draining and cleaning should take place.

What is Health Surveillance?

Health surveillance is a system of ongoing health checks that is used to:

• collect data to detect or evaluate health hazards

• protect employees' health by early detection of changes or disease

• evaluate control measures

Employers should provide health surveillance for dermatitis where there is a reasonable likelihood that dermatitis may occur in your workplace.

Dermatitis health surveillance should include:

• a baseline questionnaire and relevant skin inspection (for example of the hands, forearms, face and, if these can be contaminated, lower legs).  

You should provide workers with adequate information, instruction and training so that they report relevant symptoms.

You should seek advice from a competent person, such as an occupational health provider.

You must keep a record of occupational health surveillance. The record should contain:

• surname

• forename(s)

• gender

• date of birth

• permanent address and postcode

• national insurance number

• date when present employment started

• a historical record of jobs in this employment involving exposure to the known irritant.

Note: As the employer, if you choose to do this then it's your responsibility to maintain health records. You must keep records for at least 40 years.

Applicable Regulations:

• Health and Safety at Work etc. Act 1974

• Control of Substances Hazardous to Health Regulations 2002

Control of Substances Hazardous to Health Regulations (COSHH) requires exposure to metalworking fluids by inhalation, ingestion or skin contact to be prevented where reasonably practicable, or failing that, adequately controlled

Further free guidance available from the HSE:

MW2 Control of Skin Risks during Machining

G403 Health Surveillance for Occupational Dermatitis

CNC machining MW1 (PDF)  

Working Safely with Metal working fluids

Safe Handling & Disposal of MWF

Work right Campaign