Health Hazards of Metalworking Fluids

Metalworking fluids double up as a lubricant and a coolant for workpieces during machining operations. They are used to cool and reduce the friction between the tool and the workpiece; to extend tool life and productivity and to enhance the surface integrity of the workpiece.

Despite their advantages, metalworking fluids can have dangerous effects on the human body, especially when inhaled.

Different Types of Metal Working Fluids

1. Straight Oil

As the oldest class of engineered metal removal fluids, straight oil is used for processes that require lubrication rather than cooling; it does not need diluting with water before use.

Oily in appearance and viscous in texture due to the chlorinated and sulphur additives, straight oil consists of petroleum or vegetable oils.

2. Soluble Oil

Soluble oil comprises 30 to 85 percent of intensely purified lubricant base oil and emulsifiers, so it can mix well with water.

Soluble oil gives good lubrication and is better for cooling purposes compared with straight oil. Additives are also added to enhance performance and to prolong the life of this fluid.

3. Semisynthetic

Semisynthetic oil provides excellent lubrication, rust control and heat reduction; it has a longer sump life and is cleaner than soluble oil.

A hybrid of soluble oils and synthetics, semisynthetic oil contains 2 to 30 percent of mineral oil in a water-dilatable concentrate. The remaining portion of fluid concentrate consists mainly of emulsifiers, water, wetting agents, corrosion inhibitors and biocide additives.

4. Synthetic

Synthetic oil is the cleanest metalworking fluid; it does not contain petroleum oil. Offering the best heat reduction and excellent for rust control, it also has a longer sump life. Consisting of detergent-like components and other additives, these are used to improve the metalworking performance.

Synthetic oil is transparent and mostly unaffected by hard water.

Signs that the Metalworking Fluid is no Longer safe to use:

1. Low Sump Level

A low sump level, with 30 percent below the full mark, shows that there is evaporation of water or fluid.  A high level of concentration of chemicals, if left unattended and used, may cause serious illness to the operators. Water should be added to reach proper concentration. However, if the concentration is accurate but the fluid is lost, add fluid at an appropriate dilution.

2. Abnormal Fluid Appearance

Metalworking fluids should always be in good condition; the indications are based on the type of fluid:

  • Clear (for synthetic oil) – good condition
  • Clear to milky (for semi-synthetics) – good condition
  • Milky white with no free oil layer (for soluble oil) – good condition

A change in colour means there is a chemical reaction:

  • Grey or black fluid means there is presence of bacteria
  • A yellow or brown tint indicates that tramp oil is present
  • Dye fading shows that the fluid is aging

3. Rancidity

Foul smelling fluid indicates uncontrolled microbial growth; these microorganisms can be aerosolised into the air as part of the mist.

Exposure to these elements may cause negative health effects to machine operators and other employees. A strong odour represents a biological growth and should be treated with biocide and then revaluated – otherwise, you should discard and replace the fluid.

4. Floating Matter on the Fluid

The development of floating chips and shavings or mould growth indicates that the filtration system is not working properly.

Maintenance and period checks of the filtration system and oil skimmer are required to ensure that they are functioning as designed.

5. Tramp Oil Floating on the Surface

Tramp oil carries metallic fines that can be deposited on the skin causing mechanical irritation; this can cause dermatitis.

In order to remove the tramp oil, skim or pump the surface. If uncontrollable, it is recommended to throw off the oil.

6. Excessive Foam

If a lot of foam is present, this may be a sign of a highly concentrated fluid, contamination or an imbalance in the fluid surfactants.

7. Dirty Machines or Trenches

Dirty machines or trenches could indicate an unstable emulsion, contamination, filter failure or poor housekeeping.

Effects of Metalworking Fluids

The mist or aerosol from metalworking fluids is dangerous and can cause life threatening diseases. Some of these include irritation of the throat, eyes, lungs, nose and skin.

The severity of the complications will depend largely on a variety of factors, such as the degree and type of contamination, the kind of fluid and the level and duration of exposure.

1. Skin Disorders

Skin disorders occur when the fluid has direct contact with the skin; this happens when the proper personal protective gear is not used while working.

There are two types of skin disease that can be associated with metalworking fluids:

Contact Dermatitis

People exposed to water based, synthetic and semisynthetic metalworking fluids are at risk of developing contact dermatitis: this is a red, itchy rash caused by a substance that triggers an allergic reaction.

Although contact dermatitis is not contagious or life threatening, it should not be ignored. According to Mayo clinic, it can cause complications including neurodermatitis and bacterial/fungal infections.


Skin in contact with straight oil triggers acne that is characterised by pimples with yellow pustules that may develop on the legs, thighs, forearms and other body parts in contact with oil-soaked clothing.

2. Respiratory Diseases

According to a study, the inhalation of metalworking fluids may cause respiratory disease and could aggravate the effects of existing lung diseases. Respiratory diseases that may be triggered by metalworking fluids include:

  • Acute airway irritation
  • Asthma
  • Chronic bronchitis
  • Chronically impaired lung function
  • Hypersensitivity pneumonitis

3. Cancer

Long term exposure to metalworking fluids may cause different types of cancers such as:

  • Bladder
  • Rectum
  • Pancreas
  • Scrotum
  • Larynx
  • Skin

Control Measures to Reduce Exposure

According to Health and Safety Executive, the exposure to metalworking fluid aerosols should be limited to 0.5 mg per cubic metre of air, 10 hours a day, on a 40 hour workweek basis.

In addition, the following guidelines should be followed to minimise the health effects:

1. Minimise Amount of Fluid Mist

When metalworking fluid steams break up during operation, fine mists are produced. To reduce misting, you should:

  • Enable low-pressure delivery of metalworking fluids
  • Match the fluid to the application
  • Use formulations with low oil concentrations
  • Use mist suppressants
  • Prevent tramp oil contamination
  • Conduct proper machine maintenance

2. Use of Fume Extractor

Metalworking fluids produce a mist that can cause health problems when inhaled. Fume extraction systems filter the air and absorb fumes so that it is safer to breathe.

3. Safety Gear

Proper metal fabrication gear should be worn at all times to avoid accidents and to prevent the inhalation of fluid mist.

It is important that you prioritise your workers’ health and safety. Follow the proper maintenance and safety guidelines to control the effects of metalworking fluids.

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