Quick answer
Workplace exposure limits are airborne concentrations averaged over specified reference periods, used within exposure assessment and control. Use the current applicable entry and competent measurement/interpretation. Being below a limit does not settle skin exposure, every health risk or additional duties for substances such as asthmagens; many substances have no listed limit.
Understand what the limit measures
HSE workplace-exposure-limit guidance explains the GB framework and current EH40 source. Limits are not product dilution ratios, food-residue limits or an individual diagnosis. Different substances, forms and averaging periods need the correct entry.
Check identity, units, notes and relevant long-term or short-term periods. Do not compare a brief spot reading with an eight-hour average as if the two answer the same question.
Use a limit within an evidence-based assessment
- Identify the exact substance/form and applicable jurisdiction.
- Find the current authoritative limit and relevant notes.
- Understand tasks, people, duration and control conditions.
- Use competent sampling/measurement appropriate to the question.
- Interpret results and uncertainty and decide necessary action.
Do not use an old supplier sheet or internet table as the only check of the current limit. A substance without a WEL can still require effective control.
Look beyond the numerical comparison
HSENI COSHH guidance explains Northern Ireland’s exposure-control framework and the need for additional reduction for specified serious hazards. Check the NI application and approved guidance rather than assuming every GB change automatically has identical effect.
Air monitoring does not measure every route. Skin contact, peaks, mixed exposures and sensitisation issues may require additional assessment. A result described as “under the limit” should not conceal an unresolved control failure.
Check the meaning of a result
| Situation | Question to resolve |
|---|---|
| Different averaging period | Does the result represent the period required by the relevant limit? |
| Area sample only | Does it represent the worker’s breathing exposure? |
| Changed production | Does historic evidence cover the new conditions? |
| No listed WEL | What evidence and control standard are needed instead? |
Obtain an occupational hygienist or other competent specialist where the measurement or interpretation is beyond internal capability. This guide does not prescribe a sampling strategy or universal acceptable concentration.
Use the findings to improve control
Retain the task, method, conditions, results and decision evidence. Communicate relevant findings appropriately and act promptly when evidence shows inadequate control. Review after changes or unexpected results.
Keep workplace exposure monitoring separate from health surveillance: one examines exposure conditions, while the other addresses work-related health effects through appropriate repeated checks. Both may inform control decisions without replacing prevention.
Next steps
- Use the current correct substance entry and period.
- Obtain representative competent exposure evidence.
- Assess other routes and additional control duties.
- Record, communicate and act on findings.
Read the official practical guidance — Use the current source alongside the procedures for your own business.