Understanding Metalworking Fluids: Types, Risks, and Control Measures
Learn about the four categories of metalworking fluids, including their risks and control measures.
What are Metalworking Fluids?
Metalworking fluids (MWFs) refer to fluids used during grinding and machining and include four classes of MWFs: straight oil, soluble oil, semisynthetic, and synthetic MWFs. MWFs serve to prolong the life of the tool, carry away metal debris that results from cutting and grinding, protect the part being produced, and carry heat away from the ground or cut surface.
Occupational exposures to MWFs are a concern and need to be controlled. Repeated inhalation of MWF mists can cause respiratory illnesses and asthma, leading to non-reversible lung damage. Additionally, contact with skin can cause various skin diseases, most notably allergic dermatitis.
Types of MWFs
MWFs are grouped into four categories. The first category is “straight” oil (neat oil) MWFs. These oils are solvent-refined petroleum oils, animal, marine, vegetable oils, or synthetic oils that are not diluted with water. The straight oils may or may not contain additives that may include corrosion inhibitors, emulsifiers, buffers, and extreme pressure additives.
The next class are the soluble oils (emulsifiable oils), which are between 30 to 85 percent severely refined lubricant base oil with emulsifiers and may also contain additives. Soluble oils also contain a small percentage of water.
The semisynthetic class contains less of a percentage of the severely refined lubricant base oil (5-30%) and contains a higher percentage of emulsifiers and up to 50 percent water.
The final category is synthetic MWFs, which contain no petroleum oils and are diluted with 10-40 parts of water.
Occupational Exposure
Occupational exposures to MWFs occur either by inhaling mists and aerosols or from direct skin contact. Besides the MWF aerosols and the added additives or biocides, exposure risk can include metals and alloys from the parts ground or machined. Additionally, background contaminants in the work area and bacterial or fungal contamination in the water component of MWFs pose a risk.
The National Institute of Occupational Safety and Health (NIOSH) has established a Recommended Exposure Limit (REL) of 0.5 milligrams per cubic meter (mg/m3) for an eight-hour time-weighted average exposure. The REL applies to all categories of MWF. In addition to NIOSH, the Occupational Safety and Health Administration has established a Permissible Exposure Limit (PEL) of 5 mg/m3, which only applies to mineral oil-based MWFs. The NIOSH REL is based on regular and recent reviews of health hazard data and is the occupational exposure limit referred to for best practices.
During machining operations, the risk of Inhalation exposures is greater depending upon how close the worker is to the machine, whether there is an enclosure or splash guard, and whether the machine is operating at a high speed and making deep cuts. Other factors contributing to exposures during machining or grinding are whether there is exhaust ventilation installed to capture mists and aerosols near the point of generation and whether the exhaust system has been poorly designed or maintained. Additionally, improper machine maintenance can result in excessive fluid application or contamination of the oil with machine tramp oils.
In addition to inhalation, skin contact is a major concern with respect to exposure. Exposures occur when there are not enclosures or guards to protect from splashes during machine operation, and from handling parts, tools, or equipment without personal protective equipment (gloves and aprons), or prolonged contact with clothing contaminated with oil.
Health Effects
The NIOSH REL was established to address non-malignant respiratory disease. MWF concentrations above the REL in nine out of ten studies have been shown to cause respiratory conditions, including hypersensitivity pneumonitis (HP) which produces flu-like symptoms, acute airway irritation, chronic bronchitis, impaired lung function, and asthma. Cases of HP have been linked to water-based or diluted oils, and microbial contamination is believed to be the most likely cause. Three recent studies have shown that the risk of developing asthma is elevated and up to three times greater for workers exposed to synthetic MWFs than for workers who are not exposed.
A variety of skin diseases can result from direct skin contact with MWFs. The following factors contribute to the development of disease:
The MWF category and additives used
The duration of the skin contact
An existing skin abrasion or cut
Individual susceptibility
Inadequate or infrequent skin cleansing following contact
The use of irritating soaps or detergents
High or low humidity, hot or cold temperatures
Wearing MWF-soaked clothing or handling soaked rags.
The general cleanliness of the surrounding work area
Lack of controls i.e., machine enclosures, exhaust ventilation, personal protective equipment (gloves, sleeves, aprons)
The most reported skin diseases are irritant contact dermatitis or allergic contact dermatitis. The latter type of dermatitis is caused by an immune response to a substance that the body has become sensitized to. Dermatitis causes skin lesions and discomfort from burning and itching. Dermatitis is common with contact with soluble, semisynthetic, and synthetic MWFs.
Other skin diseases, including folliculitis (hair follicle infection), oil acne, and keratosis (rough, scaly skin patches), are linked to contact with straight oil MWFs.
Controlling Exposures to MWFs
The machine tool industry has undergone major changes in recent decades, leading to significant exposure reductions. The changes made have included the increased use of synthetic MWFs, which have increased tool and cut speeds which reduce machining time. Technological advances have also been made, leading to the development of machines with partial enclosures and the installation of local exhaust ventilation. During the 1970s and 80s, industries began installing air cleaners (mist collectors) and improving the recirculation of air and filtration.
Recommendations for Controlling Exposures
NIOSH recommends developing and implementing a comprehensive health and safety program to control exposures to MWFs. For programs to succeed, management must have a strong commitment and include worker involvement. The four main components recommended are safety and health training, worksite analysis, hazard prevention and control, and medical monitoring of exposed workers.
Worker training programs should teach workers to identify potential exposure hazards in their work areas and the adverse health effects of MWF exposure.
Worksite analysis refers to monitoring work practices and assessing personal exposures (air sampling) to assess the effectiveness of controls.
Hazard reduction can be achieved by the proper selection of MWF, i.e., using the most non-irritating, non-sensitizing fluids, regular fluid maintenance, isolation of the operation, and installation of exhaust ventilation.
With respect to PPE, workers should be trained in the proper use and care of protective equipment. If personal exposure assessment indicates that respiratory protection is needed, a respiratory protection program must be established in accordance with the OSHA Respiratory Protection standard (29 CFR 1910.134).
For more in-depth information about MWFs and controlling exposures, consult NIOSH publication 98-116, Occupational Exposure to Metalworking Fluids
Mary Dunlap is a Certified Industrial Hygienist and has been with Cornerstone Environmental, Health and Safety since 2016. When she is not working, you can find Mary enjoying the outdoors.
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The role of an industrial hygienist is to recognize potential exposure hazards, evaluate exposures, provide input for the development of controls, and finally evaluate control methods for effectiveness in reducing exposures.
When controls are warranted, the process begins with a risk assessment to characterize the problem. The hygienist can provide assistance in identifying and characterizing the hazard, the emissions and sources, worker involvement with the sources and how air movement occurs.
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All hazards can be controlled (to some degree).
There are different approaches for control.
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Controls may not always be completely effective in limiting the exposure hazard.
Administrative controls place part of the burden of control on the worker and are often not completely effective when used as a single approach. Examples of administrative controls include rotating workers, providing best practice training for performing job tasks, improving personal hygiene, and implementing housekeeping programs.
When considering options, it is necessary to evaluate the sources of exposure, the way in which it can affect the worker, and the route of entry. Typical routes may include unprotected exposure to noise, skin contact or inhalation of vapors and aerosols. The controls considered should be matched with the employee, the process or task, and be cost-effective. In some cases, there are regulatory requirements for controls such as the OSHA (Occupational Safety and Health Administration) requirement for exhaust ventilation for abrasive blasting (1910.94).
Worker rotation is frequently used to reduce the amount of time a worker is exposed to a hazard. A common example is rotating workers performing jobs in high-noise areas. Another example is to move workers every few hours who perform highly repetitive job tasks to reduce musculoskeletal strain.
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Good housekeeping and personal hygiene are also important components of administratively controlling exposures. Settled dust becomes a secondary source of exposure with increased air movement, traffic activity and vibration produced by equipment. Frequent cleaning helps to prevent dust accumulating on surfaces.
Training and reinforcing the need for personal hygiene, such as frequently washing hands and avoiding hand to mouth contact while working can reduce the risk of exposure by ingestion. Several standards contained in OSHA 1910 Subpart Z for toxic and hazardous substances mandate personal hygiene practices. Administrative controls are usually used in conjunction with engineered controls.
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Source modification refers to changing an emission source to make it less hazardous. An example of source modification is wetting dust particles released in a foundry shakeout operation to reduce dispersion. Another example may be to reduce temperatures to lower the level of chemical off-gassing and vaporization.
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Isolation refers to separating employees from hazardous processes, equipment, or environments. Isolation can be achieved by placing barriers around equipment or materials, such as the use of ventilated flammable cabinets or placing enclosures around high-noise sources. Isolation separates employees from hazards. Examples are control rooms, isolation booths and supplied air islands.
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Personal protective equipment (PPE) should always be used as the last option for control when other methods of control are not feasible or effective enough to reduce exposure to safe levels. Relying solely on earplugs or respirators places the burden of control on the worker and the protection is only as good as how properly the PPE is fit, worn, and maintained.
There are many different options to help keep workers safety, contact us to evaluate exposure concerns in your facility.
Mary Dunlap is a Certified Industrial Hygienist and has been with Cornerstone Environmental, Health and Safety since 2016. When she is not working, you can find Mary enjoying the outdoors.
Source: Case Studies: Sixty Practical Approaches of OH&S Control Principals. D. Jeff Burton, MS, PE (former CIH (Certified Industrial Hygienist), CSP)
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