Occupational Health and Safety with Metalworking Fluids: Exposure, Limit Values and Control

Metalworking fluids are the most widespread source of chemical exposure in machining. The risk lies not in acute poisoning but in skin and respiratory diseases spread over years. This article covers the routes of exposure, the accepted limit values and why they differ from one another, the hierarchy of control, the nitrosamine problem, the reading of the safety data sheet and the obligations under Turkish legislation. Fluid selection and maintenance are separate subjects; they are dealt with in the articles on cutting fluid types and fluid maintenance.

1. Routes of exposure

Three routes are decisive.

Skin contact. This is the most common form of exposure. It occurs during part removal, tool changing, measurement, machine cleaning and work with cloths or gloves saturated with fluid. Since the pH value of water-based emulsions is typically held in the 8.5–9.5 range, the fluid is mildly alkaline and dissolves the lipid layer of the skin. Metal chips, meanwhile, create mechanical irritation and micro-scratches, easing the passage of the chemical into the skin.

Aerosol inhalation. In the cutting zone, fluid becomes airborne by two mechanisms. The first is mechanical atomisation: the rotating tool and the delivery pressure break the fluid into droplets. The second is evaporation and re-condensation: fluid in contact with a hot surface evaporates and condenses in cool air as very fine droplets. Because the droplets produced by the second mechanism are smaller, they reach deeper into the lung. The thoracic fraction defined in ISO 7708 describes the particulate mass that has a 50% cut point at 10 µm and can pass the larynx; this is the fraction taken as the basis in metalworking fluid measurement.

Vapour and gas. The hydrocarbon vapour given off by straight oils and some additives when heated, the formaldehyde released from formaldehyde-releasing biocides and microbial degradation products fall under this heading. They are measured separately from the aerosol, and the fact that they are odourless does not mean exposure is absent.

2. Health effects

Irritant contact dermatitis is the most frequently seen occupational disease associated with metalworking fluids; the OSHA best practices manual reports that 14–67% of exposed workers are at risk of developing dermatitis. The range is this wide because of differences in measurement method and fluid type. Hypersensitivity pneumonitis is a rare but serious picture; the same manual states that recent HP outbreaks have been associated with the aerosols of synthetic, semi-synthetic and soluble oil based fluids. The clustering of HP cases not in a single person but within the same group of machines shows that the problem is systemic rather than individual, and it requires the fluid system to be drained and cleaned in its entirety.

A diagnostic sign: Respiratory complaints that improve during periods of leave and recur on return to work are the strongest warning sign for occupational asthma and have to be reported to the occupational physician.

3. Limit values and what they cover

The most common error in this field is using the values of different bodies interchangeably. The values do not define the same substance, the same fraction or the same reference period.

The distinctions are as follows. The NIOSH recommendation targets metalworking fluid aerosol directly and covers all categories, including water-mix emulsions; because the thoracic fraction is taken as the basis, it measures the mass reaching the lung. The NIOSH analytical method (NMAM 5524) was developed for this purpose. The OSHA value of 5 mg/m³, by contrast, is defined for mineral oil mist; the aerosol of a water-based synthetic fluid does not fit that definition exactly and in practice constitutes a far looser threshold. The ACGIH value is likewise mineral oil based and is not specific to metalworking fluid.

The HSE approach is different. In the current version of the EH40/2005 list of workplace exposure limits, no defined WEL appears for either metalworking fluid mist or mineral oil mist. The HSE guidance pages devoted to metalworking fluids also give no numerical threshold; instead, under the COSHH regulations, exposure is required to be reduced to the lowest level reasonably practicable, control measures to be verified by examination and testing, and health surveillance to be carried out.

Remaining below a numerical limit value does not on its own mean protection has been achieved. It must not be overlooked that limit values define different substances and different particle fractions, and that the obligation to control does not disappear where no WEL exists.

4. Hierarchy of control

Personal protective equipment is the lowest step of the hierarchy and does not replace engineering controls. The OSHA manual states that respiratory protection is to be brought into play only where engineering and work practice controls prove inadequate, and that where oil-based aerosols such as metalworking fluid are present in the atmosphere an R or P series filter is to be selected; the N series filter, defined for oil-free aerosols, is not considered suitable in this environment. Gloves and other protective equipment, for their part, have to be resistant or impervious to the chemical contacted.

In the region where the rotating tool is located, the use of gloves is itself an entanglement risk. For that reason gloves are used not while the machine is running, but during cleaning, fluid top-up, part washing and maintenance work.

5. Skin protection and personal hygiene

Nitrile is preferred in the choice of glove material. The legislation does not name a specific material; it requires the condition of being resistant or impervious to the chemical contacted. Because of its resistance to oils and oil-based mixtures, the material that most commonly meets this condition in practice is nitrile. Natural rubber (latex) is not preferred, both because of its inadequate resistance to oil-based fluids and because of the allergy risk associated with rubber proteins. The material decision is always made together with section 8 of the product's safety data sheet and the glove manufacturer's permeation data. Once the inside of the glove becomes wet, the protection is reversed; because the fluid sits on the skin in an occluded environment, irritation increases, so a glove that becomes wet is changed immediately.

Barrier cream is not a protection method on its own; it is a complementary measure used alongside the glove, not in its place. Applying a moisturiser after the shift helps the skin regain its barrier function. Refraining from cleaning the hands with solvents or petrol derivatives, not carrying fluid-saturated cloths in pockets and changing work clothing regularly are the basic practices. The effectiveness of these measures is verified by regular skin checks.

6. N-nitrosamine formation and formulation

Alkanolamines are used as rust inhibitors and pH buffers in water-mix fluids. Where nitrite is present in the system, it reacts with secondary and tertiary alkanolamines to form N-nitrosodiethanolamine (NDELA). Laboratory studies have shown that this formation continues at alkaline pH and is accelerated by heating, acidification and the presence of certain additives. NDELA has been classified by IARC as possibly carcinogenic to humans (Group 2B), and water-diluted metalworking fluids are counted among the sources of exposure.

Three rules apply in practice. The first is that substances containing nitrite are not added to fluids containing ethanolamine; the OSHA manual states this explicitly. The second is that if a rust inhibitor is to be topped up in the workshop afterwards, the product must be verified as nitrite-free from the safety data sheet. This subject is directly related to the topic of corrosion inhibitors and protective oils. The third is awareness that fluids which contain no nitrite but do contain amines can likewise form nitrosamines with nitrogen oxides in the ambient air; exhaust gas and welding fume are to be kept away from fluid tanks.

7. Reading the safety data sheet

The safety data sheet (SDS) has an internationally accepted 16-section structure. The sections follow the same order regardless of the supplier, which allows two products to be compared directly.

Hazard statements consist of the letter "H" and three digits; skin sensitising effect and eye irritation, for example, are given with these codes. Precautionary statements are coded with the letter "P" and are grouped under the headings of prevention, response, storage and disposal. The GHS/CLP system defines nine pictograms; they take the form of a black symbol within a red-bordered diamond. The ones encountered most often with metalworking fluids are the health hazard, irritation and environment symbols.

The safety data sheet relates to the undiluted concentrate of the fluid. The hazard profile of the emulsion at the in-use concentration is different; for this reason information on the in-use concentration has to be requested from the supplier when the risk assessment is carried out.

8. Turkish legislation, health surveillance and records

The basic framework is Law No. 6331 on Occupational Health and Safety (İş Sağlığı ve Güvenliği Kanunu). The law places on the employer the obligation to carry out a risk assessment, to inform and train the worker, to provide personal protective equipment and to conduct health surveillance. Health surveillance is regulated in Article 15; examination is mandatory on recruitment, on change of job and in cases of occupational accident and occupational disease, and the interval for periodic examination is set according to the hazard class.

Chemical-specific obligations are defined by the Regulation on Health and Safety Measures in Work with Chemical Agents (Kimyasal Maddelerle Çalışmalarda Sağlık ve Güvenlik Önlemleri Hakkında Yönetmelik). The regulation covers the substitution principle, prevention of exposure at source, the obligation to measure and control, compliance with occupational exposure limit values and the keeping of records. Classification and labelling are governed by the SEA Regulation (Maddelerin ve Karışımların Sınıflandırılması, Etiketlenmesi ve Ambalajlanması Hakkında Yönetmelik, the Turkish CLP equivalent).

The obligation relating to the safety data sheet appears in two pieces of legislation. The Regulation on Safety Data Sheets for Hazardous Substances and Mixtures (Zararlı Maddeler ve Karışımlara İlişkin Güvenlik Bilgi Formları Hakkında Yönetmelik, 13/12/2014, Official Gazette 29204) requires the sheet to be prepared in Turkish and drawn up by certified persons. Article 27 of the KKDİK Regulation (Kimyasalların Kaydı, Değerlendirilmesi, İzni ve Kısıtlanması Hakkında Yönetmelik, the Turkish REACH equivalent, 23/6/2017, Official Gazette 30105 repeated) provides that the supplier shall give the sheet to the recipient in a form conforming to Annex 2 and prepared by a certified chemical assessment expert. A sheet received from the supplier in an old format or in a language other than Turkish calls for a request for updating.

Record discipline is conducted under three headings: the chemical inventory and current safety data sheets; fluid management records (concentration, pH, microbial control, tramp oil, tank change dates); and health surveillance records together with workplace measurement results. HSE practice requires the examination records of local exhaust ventilation systems to be kept for five years and worker health records for forty years; these periods show that the record system has to be designed for a long life.

In chemical selection, the product label and the safety data sheet are assessed together; the same verification sequence applies to the products under the ATH Tools chemicals category.

Sources

• NIOSH (1998) — Criteria for a Recommended Standard: Occupational Exposure to Metalworking Fluids, DHHS (NIOSH) Publication No. 98-102. cdc.gov
• NIOSH Manual of Analytical Methods — Method 5524: Metalworking Fluids (MWF), All Categories. cdc.gov
• OSHA — Metalworking Fluids: Safety and Health Best Practices Manual. osha.gov
• OSHA — Annotated PEL Tables, Table Z-1 (comparison of OSHA PEL, NIOSH REL and ACGIH TLV). osha.gov
• HSE (UK) — Metalworking fluids: Information and guidance. hse.gov.uk
• HSE (UK) — EH40/2005 Workplace exposure limits, Fourth Edition (2020). hse.gov.uk
• IARC Monographs Vol. 77 (2000) — N-Nitrosodiethanolamine. inchem.org
• Turkish legislation — Law No. 6331 on Occupational Health and Safety (mevzuat.gov.tr); KKDİK Regulation, Official Gazette 23/6/2017 – 30105 repeated, Article 27 and Annex 2 (resmigazete.gov.tr); Regulation on Safety Data Sheets for Hazardous Substances and Mixtures, Official Gazette 13/12/2014 – 29204 (resmigazete.gov.tr).