Objectives A cross sectional study was performed to determine the applicability and accuracy of expert judgment in occupational exposure assessment. The roles of educational session and determining factors were also realised.

Method Thirteen occupational hygienists were divided into two groups based on their field experience. They asked to evaluate exposure intensity in seven operating units in a tile factory before and after exposure training session. Participant’s judgments were compared to actual air sampling data in the factory; and relative errors were calculated. Inter-class correlation coefficients were calculated and relative errors compared according to participants characteristics. Stepwise regressions were performed to investigate the defining variables.

Results In all situations there were almost perfect agreement (ICC >0.80) among raters. Correlations between estimated mean exposure and relative percentage error of participants before and after training were significant at 0.01 (correlation coefficients were -0.462 and -0.443 respectively). Results showed that actual concentration and experience resulted in 22.4% prediction variance for expert error as an independent variable.

Conclusions Correctness of exposure ratings by hygienists was susceptible to error from several sources. It seems that experienced subjects had better ability to predict the exposures. In general, in lower concentrations, the rating error increased significantly. Leading causes of judgment error should be taken into account in epidemiological exposure assessment studies.