The only exposure limit written for metalworking fluid aerosol is the NIOSH recommended exposure limit of 0.4 mg/m³ thoracic, while the enforceable US limits are OSHA's PELs for mineral oil mist (5 mg/m³) and nuisance particulate (15 mg/m³ total). The NIOSH value comes from NIOSH Criteria Document 98-102 (1998) and equals about 0.5 mg/m³ as total particulate.
Straight oils, soluble oils, semi-synthetics and synthetics, the four classes of metalworking fluids, all form aerosol at the machine. The four key figures of this page are listed below.
- NIOSH REL, fluid aerosol: 0.4 mg/m³ thoracic (about 0.5 mg/m³ total), up to 10 h/day, 40-h week (NIOSH Criteria Document 98-102 (1998))
- OSHA PEL, mineral oil mist: 5 mg/m³ 8-h TWA (29 CFR 1910.1000 Table Z-1)
- OSHA PEL, other fluids (PNOR): 15 mg/m³ total, 5 mg/m³ respirable, 8-h TWA
- Great Britain: no WEL for metalworking fluids (EH40/2005, 2020)
Great Britain and Germany set no statutory limit for the fluids themselves. British good practice holds mist below 3 mg/m³ for mineral oil fluids and below 1 mg/m³ for water-mix fluids, and German values of 5 mg/m³ respirable cover refined base oils only.
Standards, regulations and exposure limits are checked against their issuing bodies, product values against the named data sheet, and every figure carries its source and date; see our methodology and fact-checking.
What Are the Exposure Limits for Metalworking Fluids?#
Metalworking fluid exposure limits come from four kinds of instrument: a US recommendation for the fluid aerosol, US enforceable limits for oil mist and nuisance particulate, UK good-practice levels, and German refined-oil values. An occupational exposure limit is an airborne concentration tied to one aerosol fraction and one averaging time.
The table lists every verified limit for metalworking fluid aerosol and mineral oil mist with its fraction, averaging time, status and instrument.
| Jurisdiction and body | Agent | Value | Fraction and averaging time | Status | Instrument and date |
|---|---|---|---|---|---|
| US, NIOSH | Metalworking fluid aerosol | 0.4 mg/m³ (about 0.5 mg/m³ total) | Thoracic particulate mass; TWA up to 10 h/day, 40-h week; aerosol only | Recommendation, not enforceable | REL, NIOSH Criteria Document 98-102 (1998) |
| US, OSHA | Oil mist, mineral | 5 mg/m³ | 8-h TWA | Enforceable | PEL, 29 CFR 1910.1000 Table Z-1 (also 1915.1000, 1926.55) |
| US, OSHA | All other metalworking fluids (particulates not otherwise regulated) | 15 mg/m³ total; 5 mg/m³ respirable | 8-h TWA | Enforceable | PEL, 29 CFR 1910.1000 Table Z-1 |
| US, OSHA advisory committee | Metalworking fluid aerosol | 0.4 mg/m³ (0.5 mg/m³ total) | Thoracic; 8-h TWA | Recommendation, never adopted | Standards Advisory Committee final report, July 1999 |
| US, NIOSH | Oil mist, mineral (CAS 8012-95-1) | 5 mg/m³ TWA; 10 mg/m³ short-term; IDLH 2,500 mg/m³ | TWA up to 10 h; short-term | Recommendation | NIOSH Pocket Guide |
| US, California | Oil mist, mineral | 5 mg/m³ | 8-h TWA, particulate | Enforceable in California | Cal/OSHA PEL |
| New Zealand, WorkSafe | Oil mist, mineral | 5 mg/m³ TWA; 10 mg/m³ STEL | Sampled without vapor | Workplace exposure standard | WES, page updated 30 June 2022 |
| Great Britain, HSE | Metalworking fluids and mineral oil mist | No WEL | Not applicable | COSHH duty to prevent or adequately control | EH40/2005, 4th edition 2020 |
| Great Britain, HSL survey | Mist, mineral oil fluids; mist, water-mix fluids (as concentrate) | Below 3 mg/m³; below 1 mg/m³ | 8-h TWA | Achievable good practice, not statutory | HSL survey, 2003 |
| Germany, AGS | Metalworking fluids | No health-based AGW | Not applicable | Not applicable | TRGS 900, last amended 5 June 2026 |
| Germany, AGS | White mineral oil (CAS 8042-47-5) | 5 mg/m³ | Respirable | AGW | TRGS 900, entry 09/15 |
| Germany, DFG | Severely refined mineral oils | 5 mg/m³ | Respirable; peak limitation category II, excursion factor 4 | MAK value (scientific) | MAK documentation 2017 |
Values in mg/m³ of air; compare a measurement only with a limit of the same fraction and averaging time.
The limits target harm from breathing mist and touching the fluid. The skin, lung and cancer risks the limits address are summarized under metalworking fluid health hazards.
NIOSH REL: 0.4 mg/m³ Thoracic for Metalworking Fluid Aerosol#
The NIOSH recommended exposure limit for metalworking fluid aerosol is 0.4 mg/m³ thoracic particulate mass, about 0.5 mg/m³ total, as a TWA for up to 10 hours a day in a 40-hour week (NIOSH Criteria Document 98-102 (1998)).
The REL covers aerosol only, not vapors, and aims to prevent or greatly reduce respiratory disorders. It is a recommendation, not enforceable, and never an OSHA limit. NIOSH accepts total particulate sampling as a substitute because thoracic samplers are scarce.
OSHA PELs: Mineral Oil Mist 5 mg/m³ and PNOR 15 mg/m³#
OSHA has no standard for metalworking fluids, so the enforceable limits are the general PELs in 29 CFR 1910.1000 Table Z-1: 5 mg/m³ for mineral oil mist and 15 mg/m³ total or 5 mg/m³ respirable for other particulates, both 8-hour TWAs.
OSHA's Best Practices Manual applies the particulates-not-otherwise-regulated (PNOR) value to all other metalworking fluids, but the manual itself is advisory and creates no legal obligations. The oil mist PEL also appears in 29 CFR 1915.1000 and 1926.55. General Duty Clause citations, state plans and the other duties are covered in OSHA and metalworking fluids.
The 1999 Advisory Committee Value That Was Never Adopted#
The OSHA Metalworking Fluids Standards Advisory Committee recommended a PEL of 0.4 mg/m³ thoracic (0.5 mg/m³ total) as an 8-hour TWA in its final report of July 1999, and OSHA never adopted it. The committee was chartered on 28 August 1997 after a UAW petition of 9 December 1993. OSHA denied the petition by letter of 16 December 2003, upheld in UAW v. Chao (3d Cir., 22 March 2004).
Oil Mist Limits From NIOSH, Cal/OSHA and New Zealand#
Mineral oil mist (CAS 8012-95-1) has a NIOSH REL of 5 mg/m³ TWA and 10 mg/m³ short-term, with an IDLH of 2,500 mg/m³. Cal/OSHA enforces 5 mg/m³ 8-hour TWA, and New Zealand sets 5 mg/m³ TWA and 10 mg/m³ STEL, sampled without vapor. These values apply to straight-oil mist, not the fluid-aerosol REL.
UK HSE: No WEL, Good-Practice Mist Levels Instead#
Great Britain sets no workplace exposure limit for metalworking fluids or mineral oil mist in EH40/2005 (4th edition, 2020). The former standards of 5 mg/m³ TWA and 10 mg/m³ STEL for highly refined mineral oil mist gave way to good-practice guidance on 15 October 2002.
That guidance rests on a 2003 Health and Safety Laboratory survey that found mist below 3 mg/m³ (mineral oil fluids) and below 1 mg/m³ (water-mix fluids, as concentrate) achievable as 8-hour TWAs; these levels are not statutory. The legal duty under COSHH 2002 is to prevent exposure or control it adequately. The MW sheets, health surveillance and EH40 entries are set out in UK rules for metalworking fluids.
Germany: No Health-Based AGW for Metalworking Fluids#
Germany's TRGS 900 list (last amended 5 June 2026) contains no health-based AGW for metalworking fluids. White mineral oil has an AGW of 5 mg/m³ respirable (entry 09/15), and severely refined mineral oils a DFG MAK value of 5 mg/m³ respirable (2017).
For the fluids themselves, DGUV Regel 109-003 sets air values for aerosol plus vapor as technical, state-of-the-art values, not as a health-based AGW.
Why Do Limits Use Thoracic, Total, Inhalable and Respirable Fractions?#
Limits name an aerosol fraction because each sampler collects a different particle size range, so one mist reads lower as thoracic than as total mass. The four fractions are listed below.
- Total particulate: everything the sampler collects; NIOSH's accepted substitute for its REL
- Inhalable: particles entering nose and mouth; about 60 % of generated mist mass in one lathe study
- Thoracic: particles passing the larynx; the NIOSH REL fraction, about 12 % in that study
- Respirable: particles reaching the gas-exchange region; the PNOR 5 mg/m³ and German refined-oil fraction, about 8 % in that study
Averaging time differs as well: the REL is a TWA for up to 10 hours, the OSHA PELs 8-hour TWAs. A result is compared only with a limit of the same fraction and averaging time.
Does Staying Below the Limit Prevent Disease?#
No: respiratory disease from metalworking fluids has occurred below the limits, with hypersensitivity pneumonitis cases, as a rule, below 0.5 mg/m³ in 8 clusters reviewed at a 1997 NIOSH workshop. Of 37 Michigan facilities with work-related asthma reports (1988 to 1994), only one exceeded the oil mist standard. Outbreak causes and symptoms are covered under respiratory disease from metalworking fluids.
NIOSH risk models at 0.1 mg/m³ for 45 years estimate a lifetime cancer risk of 3.7 % (Park, 2018) and an asthma or hypersensitivity pneumonitis risk of 45 % under continuous outbreak conditions, about 3 % when outbreaks occur in 5 % of environments (Park, 2019). IARC places untreated or mildly treated mineral oils in Group 1 (Vol. 100F, 2012) and highly refined ones in Group 3 (Suppl. 7, 1987). Symptoms at work are a question for an occupational physician.
Who Is Exposed and How?#
About 1.2 million US workers are potentially exposed to metalworking fluids, by breathing mist and vapor and by skin contact, according to NIOSH. The REL covers only the aerosol route.
In the 2003 HSL survey, water-mix mist was higher in grinding, drilling and multiple operations than in turning and milling. Formation, droplet sizes and collectors are covered under metalworking fluid mist.
A NIOSH survey of 79 shops, reported in OECD ESD No. 28 (2011), measured these extractable mist levels.
| Fluid type | Geometric mean (mg/m³) | 90th percentile (mg/m³) |
|---|---|---|
| Soluble oil | 0.19 | 0.87 |
| Semi-synthetic | 0.20 | 0.88 |
| Synthetic | 0.24 | 1.10 |
| Straight oil | 0.39 | 1.42 |
Extractable mist as measured in the survey; the NIOSH REL equals about 0.5 mg/m³ as total particulate.
The straight-oil 90th percentile, 1.42 mg/m³, is above the 0.5 mg/m³ total equivalent of the REL and below the 5 mg/m³ PEL.
How Is Exposure Checked Against a Limit?#
Exposure is checked with personal breathing-zone air samples, analyzed by NIOSH Method 5524 (Issue 2, 29 December 2014) as thoracic or total particulate, and compared with a limit of the same fraction. NIOSH Method 5026 covers straight-oil mist only.
NIOSH recommends monitoring at least annually, every 6 months at or above half the REL (0.2 mg/m³ thoracic), and after any significant change. Sampler set-up, flow rates and how to read results are on metalworking fluid air sampling.
How Is Exposure Kept Below the Limits?#
Exposure is kept below the limits in hierarchy order: change the fluid or process, enclose and extract the mist, keep the fluid in specification, organize the work, and use respirators last. The five controls are listed below.
- Change the fluid: avoid PAH-containing oils, chlorinated paraffins, alkanolamines, nitrites and formaldehyde-releasing biocides where possible (OSHA manual)
- Enclose and extract: use enclosure-type exhaust hoods; examine LEV at least every 14 months in the UK (HSE MW1)
- Keep the fluid in specification: check concentration, pH, dip slides and sump temperature weekly (HSE MW5, 03/21)
- Organize the work: wait until no mist reaches the breathing zone before opening the door (HSE MW1)
- Use respirators last: none below 0.5 mg/m³, a P- or R-series half-mask below 5 mg/m³, a HEPA PAPR below 12.5 mg/m³ (NIOSH guide via the OSHA manual)
Machine enclosures are the most effective mist control (OECD ESD No. 28 (2011)), and ANSI B11 TR2-1997 recommends only enclosure-type hoods for machining and grinding. Mist collectors are multi-stage units with a final 95 % DOP or HEPA stage.
A fluid in specification limits microbes and degraded fluid in the mist; HSE MW5 also sets tramp oil below 2 %. Concentration, pH, bacteria and tramp-oil control are organized as coolant management programs.
What Do the Rules Require Besides a Limit Value?#
Beyond limit values, the rules require exposure to be assessed and controlled. The core duty in each of three jurisdictions is listed below.
- United States: OSHA can cite a recognized hazard under the General Duty Clause, OSH Act section 5(a)(1)
- Great Britain: COSHH 2002 requires exposure to be prevented or adequately controlled, with health surveillance where workers are exposed to fluid or mist
- European Union: Directive 98/24/EC requires a risk assessment and elimination or minimization of risk (Article 6)
State Plans must be at least as effective as federal OSHA and may be stricter. Whether a shop meets these duties is a question for the competent authority.
When to Call a Provider for Exposure Monitoring or a Fluid Audit#
Exposure monitoring is due when a shop has no air results, when results reach half the NIOSH REL (0.2 mg/m³ thoracic), or after a significant process or fluid change. The OSHA manual treats exposure monitoring and a fluid management program as separate chapters.
A fluid audit checks the third control, a sump in specification. Audits, laboratory testing and sump work are scoped under coolant management services.
Which Other Air Limits Apply to Fluid Components?#
Components and by-products of a metalworking fluid carry their own air limits, notably formaldehyde from some biocides and nitrosamines formed from amines and nitrite.
Do Nitrosamines Have an Air Limit?#
Yes, in Germany: TRGS 552 (September 2018) sets a tolerance concentration of 0.75 µg/m³ and an acceptance concentration of 0.075 µg/m³ for the sum of carcinogenic N-nitrosamines.
Does Formaldehyde From Biocides Have Its Own Limit?#
Yes: formaldehyde has its own OSHA standard, 29 CFR 1910.1048, with a PEL of 0.75 ppm as an 8-hour TWA, a STEL of 2 ppm and an action level of 0.5 ppm. Classification, release tests and the EU and German values are on formaldehyde-releasing biocides in metalworking fluids.
Metalworking Fluid Exposure Limits FAQ#
These five answers cover the status and meaning of the limits.
Are PELs legally enforceable?#
Yes: OSHA PELs in 29 CFR 1910.1000 Table Z-1 are enforceable, at 5 mg/m³ for mineral oil mist and 15 mg/m³ total for other fluids. The NIOSH REL is a recommendation without legal force.
What is the difference between a PEL and a REL?#
A PEL is OSHA's enforceable limit; a REL is NIOSH's recommendation, 0.4 mg/m³ thoracic for metalworking fluid aerosol. The PELs are 8-hour TWAs, the REL a TWA for up to 10 hours.
What is the occupational exposure standard?#
An occupational exposure standard (OES) was a former UK limit type: 5 mg/m³ TWA and 10 mg/m³ STEL for highly refined mineral oil mist until 15 October 2002. Good-practice guidance replaced it.
Is the NIOSH limit 0.4 or 0.5 mg/m³?#
Both: 0.4 mg/m³ thoracic and about 0.5 mg/m³ total are the same limit in two fractions. NIOSH accepts the total value because thoracic samplers are scarce.
What is the exposure limit for vegetable oil mist?#
For the pure oil, NIOSH recommends 10 mg/m³ total and 5 mg/m³ respirable, and the OSHA PEL is 15 mg/m³ total and 5 mg/m³ respirable. A formulated vegetable-oil cutting fluid falls under the fluid-aerosol REL.