Safety Papers
New assessment

COSHH

Workplace exposure limits (WELs)

A workplace exposure limit is the highest concentration of a hazardous substance allowed in the air a worker breathes, averaged over a set time. In Great Britain the limits are approved by HSE and listed in EH40/2005, each as a long-term limit over 8 hours, a short-term limit over 15 minutes, or both.

See the limits for common substancesStart a COSHH assessment

Figures from HSE EH40/2005, fourth edition 2020, Table 1. Follows the COSHH Regulations 2002, regulations 7 and 10.

Last reviewed 20 October 2026

The two limits

EH40 sets limits over two reference periods. Each is a time-weighted average: the concentration averaged over the period, not the highest reading at any moment.

  • Long-term limit, 8 hour TWA. The average over a working day. It protects against harm that builds up with repeated exposure, such as lung disease from dust or damage to organs from solvents.
  • Short-term limit, 15 minutes. The average over any 15 minute period. It protects against effects that come on within minutes, such as eye and airway irritation. Where EH40 lists no short-term limit, it says a figure three times the long-term limit should be used.

Limits are given in parts per million (ppm) for gases and vapours and in milligrams per cubic metre (mg/m³) for all substances. Dusts are given in mg/m³ only, as an inhalable or a respirable fraction. Respirable dust is the fine part that reaches deep into the lungs, which is why the limits for silica are so much lower than for general dust.

What the notations mean

  • Sk (skin). The substance can be absorbed through the skin and cause harm in the body. Skin contact adds to the dose, so a splash on the hands counts even when the air is well below the limit. Gloves and overalls are part of the control, not an extra.
  • Sen (sensitiser). The substance can cause occupational asthma. Exposure must be reduced as low as is reasonably practicable, not just kept under the limit.
  • Carc (carcinogen). The substance can cause cancer or heritable genetic damage. As with Sen, being under the limit is not enough: exposure must be reduced as low as is reasonably practicable, and the stricter COSHH duties for carcinogens apply.

WELs for common workplace substances

The limits for the substances on this site, taken from EH40 Table 1 and checked against it on the date shown on each data sheet. Each name opens the data sheet page; the template has the limit already filled in. For anything else, use EH40 itself.

SubstanceLong-term (8 hour TWA)Short-term (15 minute)NotationsTemplate
Acetone500 ppm, 1210 mg/m³1500 ppm, 3620 mg/m³NoneAcetone template
CementInhalable dust. The respirable fraction is 4 mg/m³. Portland cement is listed by name in EH40 Table 1 at these values.10 mg/m³None listed; use 3 × long-termNoneCement template
Ethanol1000 ppm, 1920 mg/m³None listed; use 3 × long-termNoneEthanol template
Formaldehyde2 ppm, 2.5 mg/m³2 ppm, 2.5 mg/m³NoneFormaldehyde template
Hydrogen peroxide1 ppm, 1.4 mg/m³2 ppm, 2.8 mg/m³NoneHydrogen peroxide template
Isopropanol400 ppm, 999 mg/m³500 ppm, 1250 mg/m³NoneIsopropyl alcohol template
Respirable crystalline silicaRespirable fraction. The Carc notation applies where the silica is generated by a work process.0.1 mg/m³None listed; use 3 × long-termCarc (carcinogen)Silica dust template
Sodium hydroxideNone listed2 mg/m³NoneCaustic soda template
Toluene50 ppm, 191 mg/m³100 ppm, 384 mg/m³Sk (skin)Toluene template
Wood dustHardwood dust, and any mixture containing hardwood, inhalable. Pure softwood dust is 5 mg/m³. Both carry a sensitiser notation (Sen); hardwood also carries Carc.3 mg/m³None listed; use 3 × long-termSen (sensitiser), Carc (carcinogen)Wood dust template

No WEL in EH40: Diesel, Petrol, Sodium hypochlorite, Welding fume. They are still hazardous substances under COSHH; the data sheet pages explain how exposure is controlled without a limit.

What a WEL means for your COSHH assessment

COSHH regulation 7 says control of exposure is adequate only when three things are true: the principles of good control practice are applied, any WEL is not exceeded, and exposure to carcinogens, mutagens and asthmagens is reduced as low as is reasonably practicable. A WEL is a ceiling, not a target. An assessment that says only “exposure is below the WEL” has missed the first and third tests.

In practice the assessment should say which substances on the task have a WEL, whether the work could reach it, and what keeps exposure down: substitution, local exhaust ventilation, enclosure, wet cutting, then respiratory protection. Where the substance carries Sk, the assessment should also cover skin contact. The COSHH assessment generator fills in the limits and notations from EH40 for any substance on the site, and the templates by substance open with them in place.

Substances with no WEL

Only about 500 substances have a WEL. EH40 is clear that the absence of a limit does not mean a substance is safe: exposure should be kept to a level that nearly everyone could work at, day after day, without harm. Most branded products have no WEL of their own. Look at section 8 of the safety data sheet, which lists the limits for the ingredients, and assess against those.

Checking exposure

COSHH regulation 10 requires exposure to be monitored where that is needed to show control is being maintained or to protect health. Monitoring means measuring the substance in the air a worker breathes while doing the task, usually with a sampler worn near the mouth and nose. For dusts such as silica and wood, and for solvent work in confined spaces, this is how you know the controls work. HSE's guide G409, Exposure measurement: air sampling sets out what to expect from a competent consultant.

Sources

Common questions

What does WEL stand for?
Workplace exposure limit. It is the British occupational exposure limit for a hazardous substance in the air a worker breathes, approved by HSE and published in EH40/2005.
What is EH40?
EH40/2005 Workplace exposure limits is the HSE publication that lists every approved WEL in Great Britain, in Table 1, with the notations and the methods for calculating exposure. The current edition is the fourth, published in 2020. It is free to download from HSE.
Are workplace exposure limits a legal requirement?
Yes. Under COSHH regulation 7, control of exposure is adequate only if any WEL is not exceeded, the principles of good control practice are applied, and exposure to carcinogens, mutagens and asthmagens is reduced as low as is reasonably practicable. Staying under the WEL is necessary but not on its own enough.
What if a substance has no short-term limit?
EH40 says that where no specific short-term exposure limit is listed, a figure three times the long-term limit should be used for the 15 minute period.
Does no WEL mean a substance is safe?
No. EH40 says the absence of a substance from the list does not indicate that it is safe. Exposure must still be controlled to a level nearly everyone could work at, day after day, without harm. Most products have no WEL of their own; check the ingredients in section 8 of the safety data sheet.
Where do I find the WEL for a product?
Section 8 of the safety data sheet, exposure controls and personal protection, lists the exposure limits for the ingredients. For a single substance, EH40 Table 1 is the source. The data sheet pages on this site show the EH40 figures with the date they were checked.