Before ECHA started to support DG EMPL in providing scientific recommendations on OELs, the work was carried out by the Scientific Committee on Occupational Exposure Limits (SCOEL).

Since 2019, the scientific evaluation of the relationship between the health effects of hazardous chemical agents and the level of occupational exposure is conducted by ECHA and its Committee for Risk Assessment (RAC).

The Scientific Committee on Occupational Exposure Limits (SCOEL)

The Scientific Committee on Occupational Exposure Limits (SCOEL) was set up by the Commission in 1995 to evaluate the potential health effects of occupational exposure to chemicals. Its functioning was aligned with the Commission's rules on experts groups by the Commission Decision 2014/113/EU of the 3 March 2014.

The Committee was composed of 21 highly qualified, specialised, independent experts, selected on the basis of objective criteria to ensure that the Commission's proposals, decisions and policies relating to the protection of workers' health and safety from chemical agents at work were based on sound scientific evidence.

From 1995 to 2018, the Committee assisted the Commission, in particular, in evaluating the latest available scientific data and in providing recommendations or opinions on any matters relating to the toxicological evaluation of chemicals for their effects on the health of workers. This procedure included stakeholder consultations to allow interested parties to submit comments and further data.

The health-based scientific recommendations were used to underpin the regulatory initiatives on occupational exposure limit values for the protection of workers from chemical risks, to be set at Union level under the Chemical Agents Directive and the Carcinogens and Mutagens Directive (now called the Carcinogens, Mutagens or  Reprotoxic substances Directive (CMRD)).

Joint ECHA/RAC–SCOEL task force (2015-2017)

On 6 July 2015, the European Commission requested ECHA and SCOEL to establish a joint task force composed of members from ECHA's RAC and SCOEL, as well as representatives from the secretariats. Setting up this joint task force was also a follow up from the REACH Review to improve the interface between REACH and occupational health and safety legislation.

The aim of this joint task force was to improve the mutual understanding of different approaches and to work towards agreed common scientific approaches including further developing existing and new concepts in relation to workers' exposure to chemicals, as deemed necessary.

Improving the protection of workers' health has been one of the objectives of REACH, the Chemical Agents Directive (98/24/EC) and the Carcinogens, Mutagens or Reprotoxic substances Directive (2004/37/EC). A key means of achieving this objective is to enhance the quality of scientific evaluations related to human health and exposure to chemical substances, to support relevant policies to be delivered and to improve standards of worker protection in Europe.

The specific mandated tasks of the joint task force were to make a comparative critical assessment of ECHA and SCOEL methodologies in relation to “non-threshold” substances as well as a comparative assessment of methodologies related to derived no-effect levels (DNELs) and OELs and to dermal DNELs and skin notation.

RAC and SCOEL reached substantial agreement on these specific methodologies and produced two joint reports:

• In February 2017, on the comparative assessment of methodologies related to DNELs and OELs and to dermal DNELs and skin notation.
• In December 2017, on the comparative critical assessment of ECHA and SCOEL methodologies in relation to “non-threshold” substances.

The alignment of the methodologies and the key conclusions of these reports are embedded in ECHA's Guidance for preparing OEL reports.

ECHA's pilot project for five OELs (2017–2018)

In early 2017, the European Commission requested ECHA to make a scientific assessment on the OELs of five carcinogenic substances.

The substances in this pilot project were:

• 4,4'-methylene-bis-[2-chloroaniline] (MOCA);
• arsenic acid and its inorganic salts;
• benzene;
• nickel and its compounds; and
• acrylonitrile.

The assessment was based on the most recent literature, and a type of exposure limit and a concentration value, if possible, were subsequently suggested.

RAC delivered its last opinions on this project in March 2018.

As a result, OELs were adopted and published on ECHA website in:

• June 2019, for 4,4'-methylene-bis-[2-chloroaniline] (MOCA), and arsenic acid and its inorganic salts (Directive (EU) 2019/983).
• March 2022, for benzene, nickel and its compounds and acrylonitrile (Directive (EU) 2022/431).