Measurement of respirable crystalline silica concentration by X-ray diffraction: Evaluation of metrological performances

Worker exposure to Respirable Crystalline Silica (RCS) is related with increased risk for lung cancer, so it is important to correctly assess it, through measurements of RCS. There are several methods for the uncertainty evaluation of the concentration of RCS measured by X-ray diffraction, however, none involves the calculation of the sensitivity coefficients of the mathematical measurement model. Hence, the aim of this research work is to propose an improved method, in which the sensitivity coefficients are calculated as partial derivatives of the model. The method was applied to four measurements campaigns in a factory, and the results seem to be comparable with those published in literature. It arose that for low concentrations the major contribution of uncertainty is due to the X-ray diffraction calibration line. This may mean that the minimum number of six calibration test filters, as suggested by the standards, is not sufficient, especially for low concentrations.