Emission rates of respirable crystalline silica and dust from engineered stone fabrication

Engineered stone, a composite material containing high levels of crystalline silica, has led to a surge in silicosis among workers who perform cutting, grinding, and other finishing tasks. To improve our understanding of respirable crystalline silica (RCS) and respirable dust exposures and exposure determinants for these tasks, this study extracted data from previously published studies and (i) calculated the emission rate of respirable dust and RCS (mass per time) from experimental simulation studies, (ii) assessed whether control technology or task are determinants of emission rate, and (iii) applied a 2-zone mathematical model to estimate RCS exposures using the calculated emission rates and evaluated the model predictions against task-duration exposure measurements. Emission rates were calculated from 4 published experimental simulation studies, and regression analysis showed that emission rates of RCS were positively associated with slab crystalline silica content and negatively associated with the use of control technologies. Near-field RCS concentrations predicted by model tended to underestimate exposures, but the distribution overlapped with field-based exposure measurements. The model performance is reasonable, though further simulation studies or field-based studies with detailed exposure determinant data can be used to improve emission rate estimates and model performance. The emission rates calculated in this study can be used to reconstruct past exposures for epidemiologic and risk analyses, and assist with attribution of silicosis and lung cancer to work-related causes. A multifaceted approach is necessary to ensure that employers are providing workplaces that eliminate hazardous exposures to RCS and other components of engineered stone.