Introduction The quantification of the number of workers that are exposed to dangerous substances is a key element for evidence based policy decisions, particularly in the area of occupational safety and health legislation and regulation of chemicals in general. In the past three decades a lot of scientific efforts were made to quantify the number of exposed workers at national, at EU and at international level. The methodological difficulties can be categorised in three major topics:

• The availability of reliable and representative exposure data

• The availability of substance and sector specific production and usage data

• The availability of detailed statistics on sectoral employment, occupations and major working tasks.

Methods The EU-OSHA approach is characterised by a combination of production and usage data from PRODCOM, SPIN and ECHA with survey data from the European Working Conditions Survey (EWCS), the Labour Force Survey (LFS) and the European Survey on New and Emerging Risks (ESENER). Moreover, these data are combined with structural business data of EUROSTAT. In a second step the findings are correlated with national datasets, e.g. from follow-up projects of CAREX or national cancer registers. Still the results of this correlation have to be justified by sector experts’ assessment. Further datasets at European level (the planned EU OSH Info-System) or specific surveys on certain substances will improve the reliability and comprehensiveness.

Results Improved reliability and precision of quantitative assessment of the occurrence of exposure to substances in certain sectors and occupations, and the best possible estimate of the number workers exposed to these substances.

Discussion Public data on chemical substances is constantly increasing and providing more precision. It will be possible to update and improve the figures from previous estimation approach.