Preventing Health Hazards from Metal Working Fluids

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Metal working fluids used without controls
Metal working fluids used without controls

More than 100 million gallons of metal working fluids (MWFs) are produced every year, and more than 1 million employees are exposed to these MWFs. The National Institute for Occupational Safety and Health (NIOSH) has conducted more than 70 on-site health hazard evaluations (HHEs) of facilities with occupational exposures to MWFs or mineral oil aerosols. Although NIOSH issued guidance on recommended exposure limits (RELs) and controls for MWFs in 1998, we continue to find employees exposed to airborne concentrations of MWFs above the RELs and employees with respiratory and skin problems of the types associated with MWF exposures.

MWFs are used to lubricate, cool, prevent corrosion of, and remove chips from tools and metal parts during grinding, cutting, or boring operations. There are several types of MWFs: straight or soluble oils, semisynthetic oils, and synthetic oils. Exposures to MWFs can occur through inhaling aerosols, skin contact with contaminated surfaces, and splashing of fluids. Employees who have been exposed to MWFs often report skin disorders (skin irritations, oil acne, and rashes); eye, nose, and throat irritation; and respiratory symptoms (cough, asthma, or other breathing problems).

In 1998, NIOSH issued RELs of 0.5 mg/m3 for total MWF particulates and 0.4 mg/m3 for the thoracic particulate mass, as a time-weighted average concentration for up to 10 hours per day during a 40-hour work week. (The NIOSH Criteria Document can be found at NIOSH also stated that, where possible, aerosol MWF concentrations should be kept below the REL. This level will be protective for most workers exposed to MWF aerosols. There is no exposure limit for dermal exposure to MWFs at this time. Dermal contact should be limited to prevent allergic and irritant skin reactions.

Effective fluid management guidelines and exposure control measures exist, yet we continue to see ineffective workplace practices and conditions. Between 1998 and 2006, NIOSH received 23 HHE requests concerning exposure to MWFs. The results of the 23 NIOSH evaluations indicated that 13 of the 15 facilities where air samples were collected had MWF air concentrations above the REL. Spirometry (a procedure used to measure lung function) and medical record reviews revealed respiratory symptoms in 13 of the facilities, skin symptoms in 12, findings consistent with occupational asthma in 3, and hypersensitivity pneumonitis in 3.

Although great strides have been made in improving working conditions in facilities that use MWFs, continuing improvements are needed to ensure that all employees exposed to MWFs are not at risk of developing adverse health effects. Many work sites still have inadequate ventilation, poor MWF maintenance, and lack of machine enclosures. These issues combined with inadequate medical surveillance and fluids monitoring exacerbate employee exposure to MWFs. Limitations on access to proprietary information and incomplete Material Safety Data Sheets (MSDS) make it difficult for employers to be aware of potential exposures and therefore unable to provide appropriate protection for their employees. Lack of sufficient information on MSDSs also complicates the search for causative agents when MWF-related health problems arise. It has become evident that health effects may develop in employees whose exposures are below current occupational exposure limits.

NIOSH is working to develop a standardized approach to evaluate exposures, to develop exposure-response relationships, and to provide effective and practical solutions for MWF problems. Working with and through the National Toxicology Program, NIOSH is conducting research on the irritant and allergenic properties of MWFs and is also studying their potential for carcinogenicity. Methods are being developed to characterize, classify, and measure concentrations in solutions, as liquid aerosols and for the volatile components in air, to detect changes in the composition, and to identify biocide concentrations in MWFs.

As we move forward with this research, we pose the following questions to you:

  • What are the barriers to implementing guidelines on any of the following issues: fluid maintenance, ventilation, enclosures, training, and recognition of adverse health effects?
  • Are you seeing respiratory and skin problems at your facility when MWF exposures are below the REL?

We are also interested in learning about success stories concerning worker safety and health in the MWF industry.

—Nancy Clark Burton, PhD, MPH, CIH; Judith Eisenberg, MD, MS; Stefanie Evans, MA; Manny Rodriguez, MS, CIH, CSP; Loren Tapp, MD, MS

The authors all work in the NIOSH Division of Surveillance, Hazard Evaluations, and Field Studies (DSHEFS), Hazard Evaluations and Technical Assistance Branch (HETAB). Nancy Clark Burton is an industrial hygiene team leader. Judith Eisenberg is a medical officer. Stefanie Evans is a health communications specialist. Manny Rodriguez is an industrial hygienist. Loren Tapp is a medical officer.


  1. Cohen H, White EM [2006]. Metalworking fluid mist occupational exposure limits: a discussion of alternative methods. J Occup Environ Hyg. 3(9):501-507.
  2. ILMA [2000]. 1999 Volume Survey: Report on the Volume of Lubricants Manufactured in the United States and Canada by Independent Lubricant Manufacturers in 1999. Alexandria, VA: Independent Lubricant Manufacturers Association.
  3. NIOSH [1998]. Criteria for a recommended standard: occupational exposure to metalworking fluids. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. DHHS (NIOSH) Pub. No. 98-102. []
  4. NIOSH [2007]. Health hazard evaluation and technical assistance report: HETA 005-0227-3049, Diamond Chain Company, Indianapolis, Indiana. []
  5. NIOSH [2008]. Health hazard evaluation report: HETA-2006-0332-3058, evaluation of worker exposures to noise, metalworking fluids, welding fumes, and acids during metal conduit manufacturing, Republic Conduit, Louisville, Kentucky. []
  6. OSHA [1999]. Metalworking Fluids: Safety and Health Best Practices Manual. Salt Lake City: U.S. Department of Labor, Occupational Safety and Health Administration. []
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18 comments on “Preventing Health Hazards from Metal Working Fluids”

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    The fluids that cool and lubricate cutting tools and remove metal chips inevitably enter the air in the form of a fine mist. Misting results from the high cutting pressures and machining speeds required, the geometry of the rotating tool and workpiece, chip formation, oil quantity and oil pressure ratios. Machining processes with undefined cutting edges, such as grinding, generate significant amounts of oil mist. Also, a large part of the energy expended when cutting is converted into heat, so tools and components can get extremely hot and partially evaporate cutting fluids.

    Thanks to NIOSH for adding this to the blog page. It would be very helpful for NIOSH to update the criteria document with a hazard alert highlighting data in hand since 1998.

    Splash, mist and spray are inevitable, controlling bacterial contamination is a challenge. Exhaust ventilation can reduce worker exposure, but often is retro-fitted and does not perform well. I suggest there is more of a need for practical ‘safety by design’ in equipment. For example, I have seen CNC machines which are well enclosed, but the door can be opened too soon before mists disperse. Also, the observation window gets covered in fluid restricting vision, so I have seen the worker peering down a vent at the end of the machine, thus getting spray directed at him.

    NIOSH as usual is the government organization leading the way with this blog and its websites of useful information about MWFs. The recent MRF Symposium (Dearborn MI 10/6-8/08) provided up to date information about the research and activities conducted since the late 1990’s. I urge NIOSH to provide a weblink to the symposium website so more people can obtain the information presented. I urge the symposium organizers to provide this information at the lowest possible cost so as to enlighten as many people as possible. Better sharing of information is a key way of reducing the problems we have all observed and that NIOSH notes in their description on this blog. Thank you to NIOSH and others for their efforts to protect workers in the MWF environment.

    We agree that the recent symposium, “The Industrial Metalworking Environment: The 3rd Symposium on the Assessment and Control of Metal Removal Fluids,” provided valuable information. Details on the symposium can be found at

    Has any research been done to determine the effects of chronic low-level exposure that an employee might experience over several years? If so, do the effects vary with the route of exposure (inhalation, absorption, etc.)?

    Some studies have suggested that health effects do occur at levels that fall below occupational exposure limits for total MWF and oil mist (Cohen and White, 2006; NIOSH 1998). Yet to our knowledge there is no published research that has been conducted to determine the effects of chronic low-level exposures to MWFs.

    NIOSH agrees that there is a need for more systematic research to determine the effects of chronic low-level exposures. Is anyone aware of any past or current studies being conducted that examine this important occupational issue?

    I am a graduate student at Old Dominion University in a Risk Assessment course. Reading about Metal Working Fluids on the NIOSH website I noticed it talked about the use of gloves, aprons, clothing, education, etc to protect the workers and control exposure. However, I see no indication in the article that workers are required to use PPE when working. Is PPE and option or do they have to wear it and do they also use respirators?

    Exposure to the mist, and aerosols has been found to be a risk as stated in the article, so why are businesses able to run and operate if ventilation systems, MWF maintenance, and machine enclosures are not up to par? How are facilities regulated? Also, MSDS are incomplete and limited on access to proprietary information. Is this due to lack of research in this area, lack of understanding on the topic, or lack of regulation?

    Water-based metal working fluids support microbial growth. What is the risk of being exposed to this bacteria? Finally, what are the long-term exposure risks of inhalation, or dermal contact? In 1998 the exposure limit was not known for dermal exposure, is that value now known?

    Gloves, aprons, clothing, and respirators are types of personal protective equipment (PPE) that are commonly used in MWF operations. Substitution with less hazardous materials, isolating the hazard, and using local exhaust ventilation systems, such as mist collectors, are preferred methods for controlling exposures. The need for PPE depends on the effectiveness of these engineering controls and work practices.

    Facilities using oil-based MWFs may be regulated according to the OSHA standard for oil mist which is 5 mg/m3. Currently there is no OSHA standard for MWFs. NIOSH has two recommended exposure limits (RELs) for MWFs – one for total particulates of 0.5 mg/m3 and one for the thoracic fraction of MWFs (particles small enough to pass through nasal and throat tissue and enter the bronchial tubes and into the lungs) of 0.4 mg/m3. (NIOSH, 1998). The REL is intended to prevent or greatly reduce respiratory disorders associated with MWF exposure. Some workers have developed work-related asthma, hypersensitivity pneumonitis, or other adverse respiratory effects when exposed to MWFs at lower concentrations . This REL is technologically feasible for most metalworking operations.

    We agree that material safety data sheets (MSDSs) sometimes lack information due to poor regulation or proprietary rights. We hope that current efforts to develop internationally-harmonized classification and labeling approaches (i.e., the globally harmonized system of classification and labeling of chemicals) will result in future MSDSs that are more comprehensive.

    You asked about the risk of being exposed to bacteria. Bacteria and fungi, as well as endotoxins released by bacteria, pose a respiratory hazard and risk of infection. Respiratory problems may include asthma and hypersensitivity pneumonitis.

    Dermal health effects are generally short term, such as irritation or allergies. There is no exposure limit for dermal exposure. Such a limit would be difficult to establish because MWFs are a mixture of many chemicals with varying properties and health effects. Certain chemicals, such as those with a low or high pH, irritate the skin upon direct contact. Strong detergents and hand cleansers may also cause dermatitis or aggravate an existing skin condition. Chemicals that are sensitizers elicit an antibody immune reaction. Another skin condition caused by petroleum based products is occupational acne. Depending on the type of MWFs and the machining process being used, metals such as aluminum, nickel, chromium, zinc, and cobalt may contaminate MWFs. Some of these metals, such as nickel and chromium, are sensitizers which can cause some people exposed to them to develop an allergic reaction after repeated exposures to these metals.

    We hope we have adequately answered your questions. You can learn more about the health effects and control measures for MWFs on the NIOSH topic page for MWFs. You can also review some of our health hazard evaluations reports pertaining to MWFs at our HHE web site by using the search function.

    Has anyone investigated infections or hypersensitivity pneumonitis due to bacteria in MWFs? If so, we would like to hear about your experiences.

    There is good information available on metal working fluids on the UK HSE website –

    The UK HSE investigated an outbreak of occupational lung disease at a metalworking plant in the UK and concluded that the cause of the illnesses was exposure to these fluids. Although they could not isolate the precise agent responsible the risks were linked to bacterial contamination and the use of used metal working fluids.

    They concluded that, for the UK metal working industry:

    ◦Risk assessments must deal with the risks of occupational asthma and extrinsic allergic alveolitis;
    ◦Direct means of monitoring bacterial contamination in metal working fluids, such as dip slides, must (note the word “must”) be used;
    ◦Exposure to mist needs to be prevented or better controlled; and
    ◦Health surveillance must (note word again) be carried out where there is exposure to mist.

    The fluids that cool and lubricate cutting tools and remove metal chips inevitably enter the air in the form of a fine mist. Misting results from the high cutting pressures and machining speeds required, the geometry of the rotating tool and workpiece, chip formation, oil quantity and oil pressure ratios. Machining processes with undefined cutting edges, such as grinding, generate significant amounts of oil mist. Also, a large part of the energy expended when cutting is converted into heat, so tools and components can get extremely hot and partially evaporate cutting fluids.

    I found the the symposium presentations at the website provided above – but they are only accessible if you have an ILMA membership – which is only available to the lubricant suppliers/industry and is $2000+. 🙁

    thanks you so much
    i don’t know why i can’t find exact information about metl working fluid?!
    this is subject of my presentation

    More information on metalworking fluids including NIOSH documents and other resources can be found on the NIOSH Metalworking Fluids Topic Page.

    More information on metalworking fluids including NIOSH documents and other resources can be found on the NIOSH Metalworking Fluids Topic Page.

    For machining fluid and metalworking fluid information you should check out the

    jpeters do you think that any company would ever actually do this? Should it not be checked more often that companies are using devices like this to ensure that these people are not exposed to high levels?

    Water based cutting oil is a big problem when using CNC Machines. at this time I am in dispute with the company I work for regarding this problem.

    When the weather turns cold the Gas air heaters are activated and air born cutting oil mist is sucked in the water evaporates and oil drips from the heaters.

    All the workforce is exposed to the air bourn oil/water mist will it can it cause lung health problems finding out is a problem also along with the mist the machines have a green bacteria growth in them that most companies tend to ignore

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Page last reviewed: August 13, 2020
Page last updated: August 13, 2020