Limit Values United Kingdom - WEL

UK laws and standards to secure the health, safety and welfare of people at work and the public are formally proposed by the Health and Safety Executive (HSE) Board which is a tripartite body of ten members comprising employer, employee and independent interests. The Board appoints advisory committees for various industry sectors and topics.

Workplace Exposure Limits (WELs) and Biological Monitoring Guidance Values (BMGVs) are recommended to the Board following agreement by the tripartite Advisory Committee on Toxic Substances (ACTS). ACTS may seek the advice of its technical sub-committee the Working Group on Action to Control Chemicals (WATCH) during the limit-setting process. After a period of public consultation the Board formally approves legally binding limit values (BMGVs are not legally binding.) A WEL is the maximum concentration of an airborne substance, averaged over a reference period, of 8 hours (time-weighted average) or 15 minutes (short-term exposure).

The majority of new WELs are derived from limits set by the European Commission under the Chemical Agents Directive (98/24/EC) and the Carcinogens and Mutagens Directive (2004/37/EC). Exceptionally, WELs can be set on a national basis for substances with particular concerns for UK workplaces where it is not possible to obtain a limit through the EU process within the required timescale.

For WELs set by the national process, the first stage is identical to the EU process. The exposure-response relationship is identified using as key reference points the No-Observed Adverse Effect Level (NOAEL) and the Lowest-Observed Adverse Effect Level (LOAEL) when practicable. For some substances it is not currently possible to identify the threshold NOAEL directly. If a NOAEL or LOAEL can be identified, then this value is taken as a starting point for estimating the highest level of exposure at which no adverse effects would be expected to occur in workers or their progeny following exposure over a working lifetime. Given that NOAELs/LOAELs are often obtained from animal studies, numerical uncertainty factors are applied to account for species differences and human variability.

Having determined or predicted the NOAEL, consideration is given to whether either current or improved workplace controls would achieve the NOAEL. If ACTS considers that this level of exposure is reasonably practicable then the WEL will be proposed at this level. However, there are some categories of substance for which it is not possible to derive a WEL based on NOAEL/LOAEL concepts, namely genotoxic carcinogens, asthmagens, mixtures of variable composition and substances with inadequate toxicity data sets. In such cases the WEL would be based at a level corresponding to good control, taking into account the severity of the likely health hazards and the costs and efficacy of control solutions. Wherever possible the WEL would not be set at a level where there is positive evidence of adverse effects on human health.

The technical bases for WELs and BMGVs are published in the series Summary Criteria for Occupational Exposure Limits, Environmental Hygiene Guidance Note, EH64, ISBN 071762569. Non-binding BMGVs are set where they are likely to be of practical value, suitable monitoring methods exist and sufficient data are available. When a health-based European Indicative Occupational Limit Value (IOELV) is proposed for implementation, the findings of the European Commission’s Scientific Committee for Occupational Exposure limits (SCOEL) are normally transposed into the EH64 summary document. Numerical values of WELs and BMGVs are listed in Table 1 and Table 2 of the guidance document EH40/2005¹ “Workplace exposure limits”. Additionally, Table 1 includes binding limits derived from the Carcinogens and Mutagens Directive. The current Tables of WELs and BMGVs can be accessed and ordered from the HSE website
(Book 1: List of approved workplace exposure limits and
Book 2: Biological monitoring guidance values; this is updated annually).

There is no fixed timetable for the publication of public consultation documents on new or revised WELs or BMGVs. WELs are implemented in law either by publication of a new edition of EH40 Workplace Exposure Limits, or by the issue of a supplementary revised list of WELs and BMGVs. It should be noted that in the UK the emphasis is on the application of good occupational hygiene practice as defined in Schedule 2A of the Control of Substances Hazardous to Health (COSHH) Regulations.

¹ EH40/2005, Workplace exposure limits, ISBN 0717629775

August 2013