Workplace Exposure Limits: How to Use EH40 in COSHH

Workplace exposure limits (WELs) are GB limits for concentrations of specified substances in workplace air over a defined period. They are a tool for checking inhalation exposure, not a complete COSHH assessment. The assessor must still identify the task, release routes, people exposed and controls, including routes that an air limit does not cover.

What does a WEL tell you?

The Health and Safety Executive (HSE) explains that WELs are approved GB occupational exposure limits and are listed in EH40. The list is legally binding under COSHH. A WEL is an airborne concentration averaged over a specified time, so the number only makes sense with its substance, units and averaging period.

An eight-hour time-weighted limit addresses exposure across a working day; a short-term limit addresses a shorter period where listed. A brief high release may matter even if a shift average appears low. The assessment should describe when and where peaks occur, such as during decanting, cleaning or maintenance. Check the current EH40 entry and any notes before comparing a result.

The existence of a limit does not mean exposure below it is harmless in all circumstances. HSE states that for substances classified as carcinogens, mutagens or asthmagens, exposure must be controlled to as low as is reasonably practicable. Skin contact and other routes may also matter. Use the WEL as one part of a broader control judgement.

Why should an SDS value be checked against EH40?

A supplier safety data sheet (SDS) may list exposure values from several countries or schemes in Section 8. The product may contain multiple substances with different limits. A number copied into an assessment without its jurisdiction, substance identity and time basis can mislead. HSE's SDS guidance says the sheet supplies information for the employer's assessment; it is not the assessment itself.

Confirm the ingredient or substance, relevant form and current GB WEL in EH40. Check whether the work creates a different hazardous substance from the supplied product, such as a process fume or dust. An SDS for a parent product may not describe the whole airborne mixture produced by heating, sanding or spraying it.

If no WEL is listed, do not mark the task “no limit, therefore safe”. HSE notes that only a limited number of substances have WELs. Apply the COSHH principles of preventing or adequately controlling exposure, using hazard information and competent advice where needed.

How can exposure be compared with a limit?

The monitoring question must be clear: which worker, task, substance and time period? HSE's exposure monitoring guide explains that personal air monitoring measures what a worker inhales over the sampling period, while screening instruments provide indicators. A valid comparison needs suitable sampling and analysis, representative conditions and the correct averaging period.

Use competent support for a monitoring strategy where required. A result below a WEL from one quiet shift does not necessarily describe a busy maintenance job. Record process conditions, ventilation status, worker role and uncertainty so the result can be interpreted. A result above a limit requires prompt action on exposure controls; a result below it still calls for checks that controls are maintained and other routes are addressed.

Sampling should test a control question, not simply produce a number for an audit. For example, did enclosing a transfer reduce vapour at the operator's breathing zone? If the result conflicts with visible dust or worker reports, investigate rather than choosing the reassuring evidence.

How does a WEL fit into the COSHH record?

Document the current source and date of the WEL, the substance identity, units, time basis, relevant task and how exposure is controlled. If monitoring has been done, record where the full report can be found and what action followed. HSE's assessment guide says workers must be made aware of monitoring results. Explain what the numbers mean for their work in plain language.

Review when EH40 changes, an SDS is revised, the material or process changes or controls show deterioration. The Safe Foundry feature overview shows how product and assessment records can be linked, while the measurement and interpretation need competent, task-specific evidence.

The sound conclusion is not “under the limit, job done”. It is “this is the relevant limit, these are the measured and unmeasured routes, and these controls are being maintained and checked”.

What would a WEL check look like in a workshop?

Imagine a workshop using a solvent-containing coating in two ways: occasional brush application and daily spray application. The product SDS lists several ingredient exposure values. The assessor first confirms the exact ingredients and current GB WELs in EH40, then maps where airborne release occurs. The brush and spray tasks may require different control and monitoring decisions even though they use the same can. The record should not attach one copied number to the product and assume it covers both activities.

For a relevant substance, define the question before sampling. Does the worker's normal shift exposure stay below the eight-hour limit, and are there short periods needing comparison with a short-term limit? Are maintenance and clean-up part of the worker's exposure? A competent monitoring plan selects people and periods that represent those questions. Document any condition that makes a sample unusual.

What can a number fail to show?

A result is limited by what was measured. An air sample for one ingredient may not capture another contaminant produced by the process. An average may hide a short peak. A worker's skin may contact liquid while the air result is low. A quiet sampling day may differ from a production peak. Record these limitations alongside the comparison so the conclusion remains proportionate.

Also distinguish a WEL from a desired operating target. The duty is to control exposure adequately, and for certain serious hazards to reduce it as low as reasonably practicable. A limit should not become a reason to ignore feasible source improvements. If extraction, enclosure or work practice can reduce release, assess those options even when a measured value is below the limit.

How should a changed EH40 entry be handled?

Identify tasks that involve the substance, not just every file that mentions its name. Review the existing control basis and any monitoring results against the current value and notes. Decide whether work methods, equipment or further measurement need changing, then tell affected workers what the new conclusion means. Keep the old evidence with its date so a future reviewer can understand why the earlier assessment differed.

This is one reason to link SDS, ingredient, task and monitoring records. The limit belongs to a substance and time basis; the control decision belongs to the work being done. Keeping those two levels distinct prevents a neat spreadsheet value from replacing the real assessment.

Give workers the result in terms of their task. Explain which substance was measured, during which activity, how the value was compared with the relevant WEL and what control action follows. Avoid presenting a single percentage as a permanent safety rating. If conditions change, the comparison may need to be revisited. A clear explanation also lets workers report when the sampled day did not resemble their normal work.

Keep the date and edition of EH40 used for the comparison so a later reviewer can trace the decision and reassess it if the limit changes.

The assessment workflow provides a structure for task records linked to source documents.