EH40 and workplace exposure limits explained
What the numbers in EH40 mean, how they are averaged, and what COSHH asks of an employer once a limit applies. Every figure on this page is copied from the current EH40 Table 1.
What are workplace exposure limits in EH40?
Workplace exposure limits (WELs) are the maximum concentrations of hazardous substances in the air that employees in Great Britain may breathe, averaged over 8 hours or 15 minutes. HSE lists them in EH40/2005, and its Table 1 is legally binding under COSHH.
The current edition is EH40/2005, fourth edition 2020. It brought in 13 new or revised limits from 17 January 2020, including respirable crystalline silica and hardwood dust. Each entry gives a long-term limit, a short-term limit or both, in ppm, mg/m³ or fibres per millilitre. Notations flag substances that can be absorbed through the skin (Sk), cause occupational asthma (Sen) or cause cancer (Carc).
A WEL is not a safe line. HSE’s guidance in L5 says WELs “should not be considered a hard and fast line between safe and unsafe”. For listed carcinogens, mutagens and asthmagens, COSHH requires exposure to be reduced as low as is reasonably practicable, whatever the WEL. EH40 asks the same for every substance marked Carc or Sen. How the limits fit the wider duties is in the COSHH Regulations explained.
What EH40 is and why it binds
Fourth edition 2020EH40/2005 Workplace exposure limits is the HSE publication that holds the list of every WEL in Great Britain. COSHH regulation 2 defines a workplace exposure limit as the limit HSE has approved, “as contained in HSE publication EH/40 Workplace Exposure Limits 2005 as updated from time to time”. That is why the list carries the force of law.
Only part of the book binds. EH40 says that COSHH imposes requirements by reference to Table 1 and the Notices of Approval, which are therefore legally binding. The remainder is guidance. The CAS numbers printed in Table 1 are not part of the approved list.
The fourth edition was published in January 2020. On 5 October 2026 HSE’s publication page still listed it as the current edition. Since leaving the EU regime, HSE sets new or revised WELs through its own process. That means specialist and economic assessment, review by independent experts, public consultation and approval by the HSE Board.
HSE says it has considered all the outstanding EU limits and will revise 3 of them. All 3 apply only to underground mining and tunnelling and are already printed in EH40. For trades working above ground, the 2020 Table 1 is the list to use.
Sources: COSHH regulation 2; EH40/2005 page 2 and paragraph 15; HSE, workplace exposure limits.
How to read a workplace exposure limit
Every Table 1 entry is read the same way: a reference period, a unit, the fraction of dust it applies to, and any notation.
Long-term limit: the 8-hour time-weighted average
The long-term limit controls effects that build up with prolonged or repeated exposure. Exposure in any 24-hour period is treated as one uniform exposure over 8 hours, the 8-hour TWA. A longer shift still divides by 8, so the same concentration over 10 hours gives a higher average.
EH40 paragraph 64 and the approved methodShort-term limit: any 15 minutes
A short-term exposure limit (STEL) protects against effects seen after brief exposure, such as eye irritation. It applies to any 15-minute period throughout the shift, not an average across it. Where Table 1 gives no STEL, EH40 recommends three times the long-term limit as a guideline for controlling short peaks. That figure is guidance, not a legal limit.
EH40 paragraphs 4, 14, 64 and 66ppm and mg/m³
Gases and vapours are set in parts per million (ppm) and converted to milligrams per cubic metre (mg/m³) at 20°C and 1 atmosphere. Dust and fume are given in mg/m³ only. Machine-made mineral fibres and refractory ceramic fibres can also be expressed as fibres per millilitre of air.
EH40 paragraphs 67 to 69Inhalable and respirable dust
Inhalable dust is the fraction that enters the nose and mouth. Respirable dust is the finer fraction that reaches the gas exchange region of the lung. A dust WEL in Table 1 refers to the inhalable fraction unless it says respirable.
EH40 paragraphs 16, 44 and 45Sk: absorbed through the skin
The substance can pass through intact skin and cause harm elsewhere in the body. The WEL covers breathing only, so a splash on the skin or soaked clothing adds to the dose without showing in an air sample. Gloves and skin checks matter as much as extraction.
EH40 annotations and paragraphs 73 and 74Sen: can cause occupational asthma
Once a worker is sensitised, further exposure, sometimes even in tiny quantities, may bring on symptoms. COSHH requires exposure to a substance that can cause occupational asthma to be reduced as low as is reasonably practicable. EH40 says health surveillance is appropriate for everyone exposed or liable to be exposed to such a substance. The L5 Approved Code of Practice adds that once a worker has developed occupational asthma, suitable levels are likely to be well below any WEL.
EH40 paragraphs 53 to 56; COSHH regulation 7(7)(c); L5 ACOP paragraph 144Carc: can cause cancer or heritable genetic damage
The notation marks substances capable of causing cancer or heritable genetic damage. Regulation 7(5) adds measures for carcinogens and mutagens where exposure cannot reasonably be prevented. One is no eating, drinking or smoking in areas that may be contaminated. Regulation 7(7)(c) requires exposure as low as is reasonably practicable for anything with hazard statement H340, H350 or H350i, or listed in Schedule 1. EH40 applies the same requirement to every substance with a Carc notation.
EH40 annotations and paragraphs 48 to 51 and 84; COSHH regulation 7(5) and 7(7)(c)BMGV: a biological monitoring guidance value
A guidance value for a substance or its breakdown product in urine, blood or breath, listed in EH40 Table 2. BMGVs are not statutory, and testing needs the informed consent of the worker. A result above the value signals that controls need investigating.
EH40 paragraphs 80 to 83 and Table 2EH40 says the Carc, Sen and Sk notations are not exhaustive. Check section 8 of the safety data sheet and the hazard statements on the label as well.
Workplace exposure limits trades meet
From EH40 Table 1Copied from EH40/2005 Table 1, fourth edition 2020, on 5 October 2026. Where Table 1 sets no limit for a period it prints a dash, shown here as “None listed”. Dust limits are for the inhalable fraction unless marked respirable.
| Substance | Where trades meet it | Long-term limit (8-hour TWA) | Short-term limit (15 minutes) | Notation |
|---|---|---|---|---|
| Silica, respirable crystalline (respirable fraction) | Cutting, chasing, drilling and grinding concrete, brick, block, stone, kerbs and tiles | 0.1 mg/m³ | None listed | Carc (where generated as a result of a work process) |
| Hardwood dust (inhalable fraction) | Sawing, routing and sanding oak, ash, beech and other hardwoods | 3 mg/m³ | None listed | Carc, Sen. Where hardwood dust is mixed with other wood dust, this limit applies to all of it |
| Softwood dust | Sawing and sanding pine, cedar and other softwoods | 5 mg/m³ | None listed | Sen |
| Portland cement | Mixing mortar, concrete and grout; emptying bags | 10 mg/m³ inhalable; 4 mg/m³ respirable | None listed | None |
| Calcium hydroxide (hydrated lime) | Lime mortars, renders and plasters | 5 mg/m³ inhalable; 1 mg/m³ respirable | 4 mg/m³ respirable | None |
| Gypsum and plaster of Paris | Cutting and sanding plasterboard; mixing bagged plaster | 10 mg/m³ inhalable; 4 mg/m³ respirable | None listed | None |
| Isocyanates, all (as NCO), except methyl isocyanate | Two-pack polyurethane paints and lacquers, spray foam, some floor coatings and adhesives | 0.02 mg/m³ | 0.07 mg/m³ | Sen |
| Styrene | Polyester resins for GRP roofing and fibreglass repairs | 100 ppm (430 mg/m³) | 250 ppm (1080 mg/m³) | None |
| Xylene, o-, m-, p- or mixed isomers | Solvent-based paints, thinners, adhesives and cleaners | 50 ppm (220 mg/m³) | 100 ppm (441 mg/m³) | Sk, BMGV |
| Toluene | Solvent-based adhesives, thinners and some coatings | 50 ppm (191 mg/m³) | 100 ppm (384 mg/m³) | Sk |
| Dichloromethane (methylene chloride) | Paint strippers that contain it, which a professional may use only with an HSE certificate of competence | 100 ppm (353 mg/m³) | 200 ppm (706 mg/m³) | BMGV, Sk |
| Acetone | Cleaning down resin and adhesive; degreasing | 500 ppm (1210 mg/m³) | 1500 ppm (3620 mg/m³) | None |
| Propan-2-ol (isopropyl alcohol) | Surface wipes, degreasers and cleaning sprays | 400 ppm (999 mg/m³) | 500 ppm (1250 mg/m³) | None |
| 2-Butoxyethanol | Some glass, surface and floor cleaners | 25 ppm (123 mg/m³) | 50 ppm (246 mg/m³) | Sk, BMGV |
| Sodium hydroxide | Drain cleaners, oven cleaners and heavy-duty degreasers | None listed | 2 mg/m³ | None |
| Chlorine | Given off when bleach is mixed with an acid cleaner | None listed | 0.5 ppm (1.5 mg/m³) | None |
| Carbon monoxide | Petrol cut-off saws, generators and plant run in enclosed spaces | 20 ppm (23 mg/m³) | 100 ppm (117 mg/m³) | BMGV |
| Nitrogen dioxide | One of the gases in diesel engine exhaust | 0.5 ppm (0.96 mg/m³) | 1 ppm (1.91 mg/m³) | None |
| Manganese and its inorganic compounds (as Mn) | Welding fume, including fume from mild steel | 0.2 mg/m³ inhalable; 0.05 mg/m³ respirable | None listed | None |
Notation “None” means Table 1 prints none, not that the substance is harmless. Table 1 also lists chromium (VI) compounds at 0.01 mg/m³ over 8 hours, with 0.025 mg/m³ for process-generated exposure, and gives welding fume as its example. It marks them Carc, Sen and BMGV and prints no end date for the 0.025 figure. The current EH40 does not include the lower limit of 0.005 mg/m³ set by Directive (EU) 2017/2398, which has applied in the EU since 17 January 2025. For a product, the supplier’s data sheet names each ingredient with a WEL in section 8.
What COSHH says about exposure limits
A WEL is one test of adequate control, not the whole of it. These are the provisions that use it.
A WEL must not be exceeded
Control counts as adequate only if three things hold. The Schedule 2A principles of good practice are applied. Any WEL approved for the substance is not exceeded. And, for the substances named below, exposure is reduced as low as is reasonably practicable.
Regulation 7(7)Carcinogens, mutagens and asthmagens: as low as reasonably practicable
This applies to substances carrying hazard statement H340, H350 or H350i, and to anything listed in Schedule 1, which includes hardwood dusts. It also applies to substances carrying H334, anything in section C of HSE’s Asthmagen? review, and anything the assessment shows may cause occupational asthma. EH40 applies the same requirement to every substance with a Carc or Sen notation, and says it applies whether or not the substance has a WEL.
Regulation 7(7)(c) and Schedule 1; EH40 paragraph 84What as low as reasonably practicable means
The L5 Approved Code of Practice says employers should keep improving control until the cost of further reduction becomes grossly disproportionate to the benefit. Staying just under the WEL is not enough on its own for these substances.
L5 ACOP paragraph 143The assessment must consider the WEL
The risk assessment must consider any relevant workplace exposure limit or similar occupational exposure limit. It must also consider combined exposure where the work involves more than one hazardous substance.
Regulation 6(2)(f) and (j)Monitoring where the assessment calls for it
Exposure is measured where the assessment shows it is needed to keep control adequate or to protect health. It follows a suitable procedure, at regular intervals and after any change that may affect exposure. It is not required if the employer can show adequate control by another method of evaluation. Records representing the personal exposure of identifiable employees are kept for at least 40 years, other records for at least 5 years, both from the last entry. Employees may see their own monitoring record on reasonable notice.
Regulation 10Tell employees if a WEL is exceeded
Employees must be told any relevant WEL as part of their information and training. If monitoring shows a WEL has been exceeded, the employees or their representatives must be informed forthwith.
Regulation 12(2)(a)(ii) and (d)A WEL is not a safe line
HSE’s guidance in L5 says WELs should not be considered a hard and fast line between safe and unsafe. It says the degree to which exposure is reduced below the WEL should be proportionate to the health risk. If the principles of good practice are applied correctly, exposure should be below any relevant WEL.
L5 guidance, paragraph 139Checking exposure against a WEL
The order a contractor works through when a job involves a substance with a WEL.
Find the limit
Read section 8 of the supplier’s safety data sheet for each product, and look up process dust and fume, such as silica or welding fume, in EH40 Table 1.
NoteEH40 lists many substances under other names. Quartz and cristobalite dust appear as respirable crystalline silica; xylol as xylene.
Decide whether to measure
The assessment decides whether monitoring is needed. It is not required where adequate control can be shown by another method of evaluation. The L5 Approved Code of Practice gives smoke tubes and air velocity measurements as examples.
NoteFor carcinogens, mutagens and asthmagens, the L5 Approved Code of Practice says a monitoring programme may be needed unless exposure is most unlikely ever to exceed the WEL.
Measure in the breathing zone
WELs relate to personal exposure, so samples are taken in the breathing zone of the worker doing the task. Many firms use an occupational hygiene consultant.
NoteHSE’s G409, Exposure measurement: air sampling, sets out what to expect from a competent consultant.
Work out the 8-hour average
Multiply each measured concentration by the hours it lasted, add the results for the 24-hour period, and divide by 8. Compare the result with the long-term limit.
NoteEH40’s own example: 0.12 mg/m³ for 7 hours 20 minutes and nothing for 40 minutes gives an 8-hour TWA of 0.11 mg/m³.
Check the short peaks
Compare the worst 15 minutes with the STEL. Where none is listed, EH40 recommends three times the long-term limit as a guideline. Cutting a kerb or mixing a two-pack coating can produce a sharp peak inside a modest daily average.
NoteEH40 says frequent short peaks that stay within both limits should still be controlled, unless the assessment shows no risk.
Add up mixed exposures
Check each substance against its own WEL first. Where the effects add together and the WELs rest on the same health effect, EH40 sums each concentration divided by its WEL, over the same reference period. A total above 1 exceeds the notional limit for the mixture.
NoteEH40 says the formula does not apply where the lead effect is cancer or asthma, and to get specialist advice in any doubt.
Act on the result
Review the assessment if the results call for it, improve the controls, and tell the operatives what was found. Keep the monitoring record for the period regulation 10 sets.
NoteFor a carcinogen, mutagen or asthmagen, a result below the WEL does not end the duty. Keep reducing exposure as low as is reasonably practicable.
Extraction is usually the control that brings a reading down. See local exhaust ventilation for how it is examined and tested.
When a substance has no WEL
Many thousands of substances are used at work and only about 500 have a WEL. The L5 Approved Code of Practice says the absence of a substance from the list does not mean it is safe.
Welding fume
Table 1 has no single WEL for welding fume, only for parts of it such as manganese and chromium (VI). HSE’s 2019 safety alert says all welding fume, including mild steel fume, can cause lung cancer. HSE no longer accepts any welding without suitable exposure controls, whatever the duration, “as there is no known level of safe exposure”. Indoors that means engineering controls, usually LEV, backed by RPE where extraction alone does not control the fume. Outdoors, RPE.
HSE safety alert STSU1 - 2019Diesel engine exhaust
HSE’s HSG187 says no WEL has been set for diesel engine exhaust emissions as a whole. Some of its gases, such as carbon monoxide and nitrogen dioxide, have their own WELs. HSE says to control exposure to the exhaust as a whole. On site, the usual sources are generators and plant run in enclosed or poorly ventilated areas.
HSE HSG187, Appendix 2White spirit and other hydrocarbon solvents
These blends have no single entry in Table 1. EH40 sets out a calculation suppliers can use to derive an in-house limit for a hydrocarbon solvent blend. If the supplier has set one, look for it in section 8 of the data sheet.
EH40 paragraphs 85 to 89Dust with no WEL of its own
Any dust counts as a substance hazardous to health at or above 10 mg/m³ inhalable or 4 mg/m³ respirable, as an 8-hour TWA. These are thresholds for COSHH to apply, not WELs. Where a dust contains a component with its own WEL, such as silica in stone, that limit applies too.
Regulation 2 and EH40 paragraphs 43 to 46Everything else
For substances with no WEL, the L5 Approved Code of Practice says to control exposure to a level nearly all workers could be exposed to, day after day, without adverse effects. Where no clear control approach exists, an in-house standard may help, with advice from suppliers or an occupational hygienist.
L5 ACOP paragraphs 147 and 148Every data sheet to hand,
tied to the job that uses it.
In Unibuild, each hazardous substance holds its safety data sheet and its supplier, linked to the jobs, materials and purchase orders that use it. Review dates are tracked, every version is kept, and the current one is the one out on site.
When an auditor or a principal contractor asks for the COSHH register, it is a search by name or supplier, not a spreadsheet somebody else kept.
- A data sheet for every substance held with its supplier
- Tied to the job through the materials and purchase orders that use it
- Review dates tracked and every version kept
- Searched by product name or supplier
Free COSHH templates
Free to use and reuse, no sign-upEH40 and workplace exposure limits: common questions
What is EH40?
What is the latest version of EH40?
Is EH40 a legal requirement?
What is the difference between a long-term and a short-term exposure limit?
What do Sk, Sen and Carc mean in EH40?
What is the WEL for silica dust?
What is the WEL for wood dust?
Do I have to measure exposure to prove I am below the WEL?
What if a substance is not in EH40?
How do you convert ppm to mg/m³?
The COSHH guide
Read in any orderSources
Great Britain law and HSE guidance, read on the dates above. Northern Ireland has its own COSHH Regulations.
- HSE, EH40/2005 Workplace exposure limits, fourth edition 2020 (PDF)
- HSE, EH40/2005 publication page
- HSE, Workplace exposure limits
- The Control of Substances Hazardous to Health Regulations 2002, regulation 7, legislation.gov.uk
- The Control of Substances Hazardous to Health Regulations 2002, regulation 2, legislation.gov.uk
- HSE L5, Control of substances hazardous to health, ACOP and guidance, sixth edition 2013
- HSE safety alert STSU1 - 2019, change in enforcement expectations for mild steel welding fume
- HSE HSG187, Control of diesel engine exhaust emissions in the workplace
The COSHH register,
tied to the job.
Unibuild keeps each substance’s data sheet and supplier against the jobs, materials and purchase orders that use it, with review dates tracked and every version kept.