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What is oil mist?

Oil mist removal 13 Feb 2023 General

In the metalworking industry, metalworking fluids (MWF) are used to cool and lubricate the machining activity. The metalworking fluids ensure a reduced friction between the tool and the work piece. In addition they prolong the life of the tool, carry away swarfs and protect the surfaces of the work pieces.

The metalworking fluids are a complex mixture, which may contain mineral and/or synthetic oils, additives such as biocides and rust inhibitors etc. as well as contaminants like metal fines, tramp oil and bacteria. When droplets of these metalworking fluids are airborne, it is called oil mist.

Oil mist and oil smoke: how does it form

Oil mist is caused by metalworking fluids that come into contact with fast rotating tools (e.g. milling and drilling procedures). The oil mist is then dispersed into the air.

In addition to oil mist, oil smoke may appear. These are smaller droplets than oil mist. Due to the high temperatures of the metal parts during machining (e.g. grinding procedures) the MWFs become excessively hot and start to ”burn” and degrade.

The small droplets in the air, to a diameter of approx. 1 μ, are designated as oil mist. Everything with a smaller diameter is considered to be oil smoke.

The amount of oil mist

During machining, oil mist is produced by the interaction of the fluid with the moving parts. When liquid hits fast moving parts, it is thrown back and dispersed as fine droplets. The gaseous state of any liquid is formed as molecules leave (evaporate from) the surface of the liquid. The evaporation increases with low boiling point of the liquid and increased temperature of the fluid. In water based emulsion the evaporation will increase the humidity in the plant. The generation of mists are mainly depending on:

  • Higher speed of tool = higher generation of mist
  • The volume, rate and point of delivery of metal working fluid to the cutting edge
  • Higher temperatures of the work piece = higher generation of oil smoke

Exposure limit for oil mist

Due to the different types of MWF’s, the composition of the mist is different in most cases, making it difficult to have a single recommended limit for exposure. Most countries make a difference between oil mist derived from water-miscible and mineral oil-based metalworking fluids.

Threshold Limit Value (TLV)

Every country has its own TLV value that will set the standard of the indoor air quality in the plant. The TLV values in the field of coolant mist/smoke are given in mg/m3. The measurement is always taken in or near the breathing zone of the operator. This means that the TLV value will give information about how much coolant mist/smoke is acceptable for the operator to inhale.

In the USA, the OSHA has set the Permissible Exposure Limit (PEL) for mineral oil at 5,0 mg/m3 (10hr TWA). And the NIOSH has a Recommended Exposure Limit (REL) for all types of MWF at 0,5 mg/m3 (10hr TWA). In Europe, the IFA (formerly known as BGIA) has set the limit on 10 mg/m3 for water-miscible and non-water-miscible metalworking fluids with a flame point greater than 100°C for Germany. The Institut National de Recherche et de Sécurité (INRS) in France has one of the lowest recommended exposure limits, being 1 mg/m3 of aerosol. Switzerland has a Permissible Exposure Limit for heavy mineral oils with a boiling point of over 350°C of only 0,2 mg/m3. *

Corporate Limit Value

In many countries the legislations are not up to the industrial standard or only recommendations. Therefore many multinational companies are setting their own hygienic limit value in own Global Production Standards. The reason for doing this is to make sure that air quality is kept at the best possible level, making sure that production can follow the quality standards in every country where the company is active.

Short Term Value (STV)

The STV is an accepted short term exposure to the contaminant. Normally for periods not exceeding 15 minutes and repeated maximum 4 times per day with at least 60 minutes between each exposure. Most countries also have regulations for STV but they are not as well-known as the TLV values.

Oil mist - Danger to man, machine and environment

Inside of a CNC machine
Inside of a CNC machine

Many metalworking processes generate oil mist, like milling, turning, grinding and drilling. The metalworking fluids form a mist during these processes, the larger drops can enter the nose and trachea and can be swallowed down. The smaller droplets can deposit in the lungs and also cause considerable irritation of the eyes, nose and throat. Oil mist and smoke can even contain metal particles with carcinogenic substances. If the mist settles down on the factory floor there will be an increased risk of slipping.

There are not only possible negative effect on humans, it also has a negative effect on your machinery. If the mist settles on the machines, they might be damaged due to corrosion. The sensitive electronics of the machines can also be affected by the mist. This can lead to high maintenance costs.

If the machines and surroundings are not properly maintained, the settled oil mist might increase not only the risk a fire hazard but also a bacteria and mold growth which will cause hygienic problems. Therefore, effective detection, filtration and elimination of oil mist is so important!


*) Source: (Chapter 1.2)

What is an oil mist collector

Plymovent's MistEliminator 4-series
Plymovent's MistEliminator 4-series

An oil mist collector is a device used to capture and filter the oil mist generated by various industrial processes to prevent it from contaminating the air and potentially causing health and safety hazards. It typically consists of a filter element, fan, and collection container. The oil mist is drawn into the collector, where it is separated and captured by the filter, and clean air is then released back into the environment.

Plymovent offers extraction and filtration systems for effective removal of mist from metalworking fluids.

The 6 benefits of oil mist collectors

Modular filter systems offer several benefits for CNC machineries:

  1. Flexibility: Modular filter systems can be configured to match the specific requirements of a CNC machine, providing greater flexibility in terms of installation and maintenance.
  2. Improved air quality: Modular filter systems provide a high level of filtration, removing oil mist and other particulates from the air, improving the overall air quality in the machining area.
  3. Increased lifespan of machines: The removal of oil mist and other particulates from the air can help extend the lifespan of CNC machines by reducing wear and tear on moving parts.
  4. Enhanced worker safety: By removing oil mist from the air, modular filter systems help protect workers from inhaling harmful particulates, reducing the risk of respiratory problems.
  5. Easy maintenance: Modular filter systems are designed for easy maintenance and can be quickly and easily disassembled for cleaning or replacement of filter elements.
  6. Energy efficiency: Modular filter systems can be designed with energy-efficient components, reducing energy consumption and lowering operating costs.

Overall, the use of modular filter systems in CNC machineries can improve air quality, enhance worker safety, extend the lifespan of machines, and reduce operating costs.

More information

Would you like to know more about oil mist removal systems? Then don’t hesitate to contact us!
Just send an email to, or fill out the contact form and we will get back to you as soon as possible. 

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