Tier 1 assessment tools are used frequently to provide exposure estimates as part of the substance registration process under Regulation (EC) No 1907/2006 (REACH). Using only a limited number of basic input parameters, these generic tools are designed to provide conservative exposure predictions for a wide range of exposure scenarios. This study aimed to validate tools recommended for use in REACH through comparison with inhalation and dermal exposure measurement data from a variety of sources. Restrictions on the type and sampling methods for the dermal data collected prevented their use in the validation, thus only inhalation exposure was addressed. Individual and summarised aggregated personal exposure measurements and associated contextual descriptions were obtained from several European providers and one US source. Exposure scientists from the Institute of Occupational Medicine coded the exposure scenario information using the parameter for each tool and exposure estimates were generated according to these inputs. A number of comparisons were carried out to examine the level of conservatism, including determination of the proportion of measurement values which exceeded the tool estimations and calculation of the ratio of the measurement value to the tool estimate. "High", "medium" and "low" levels of conservatism were defined as where ≤10%; 11≤25% and >25% of the measurements exceeded the tool estimate, respectively. The impacts of various tool-implemented exposure determinants on the percentage of exceedances were investigated.

The Results suggested that across all of the physical forms and emission generation processes (collectively "exposure categories"), the tools appeared to be conservative, but with varying levels of conservatism observed. The tools appeared least conservative when estimating exposures during activities involving non-volatile liquids, which were evaluated only for the MEASE and STOFFENMANAGER tools and metal abrasion (ECETOC TRAv2 and v3 tools). The EMKG-EXPO-TOOL appeared to be sufficiently conservative for volatile liquids but less conservative for powders than the other tools. Differences in the level of conservatism for all of the tools were observed between data providers, PROC codes, domain, and the presence/ absence of local exhaust ventilation (LEV). The observed impact of domain and LEV on the level of conservatism suggests that these two aspects of tool operation require review, in particular, the assumptions made regarding the initial domain-specific estimates and the modifiers applied for LEV implementation should be re-evaluated. Correlations between the measurement results and tool predictions were generally stronger for powders and non-volatile liquids than for the other exposure categories. The comparator dataset was limited in some respects: relatively few comparator measurements were available for exposure to non-volatile liquids, metal dust and metal fume. The study results provide useful information both for tool developers and for users, particularly in terms of applications where the tools should perhaps be used with extra caution.