Introduction & Objective: Determination of free silica to calculate threshold limit value is necessary. The purpose of this research was study of free silica in particulate emission in ambient air of stone crushing workshops in Azandarian area.

Materials & Methods: 40 samples of respirable dust from workplace air were obtained in breathing zone of workers in different job stations. Samples were taken with personal samples pumps attach to cyclones and analyzed by a gravitmetric method and X –Ray Diffraction.

Results: The results were showed that mean concentration of respirable dust and quartz in workshops (type 2) was equal to 1.17-1.24 mg/m3 and 0.94-1.03 mg/m3 respectively, and also in workshops (type 1) was equal to 0.81-1.07mg/m3 and 0.79-1.05 mg/m3 respectively. Free silica rate in ambient air of workshops type1 and type2 was 97.5% and 81.3% respectively. Difference of free silica rate in two types of workshops was statistically significant (p=0.0001).

Conclusion: The comparison of time weighted average of respirable dust concentration with threshold limit value showed concentration of respirable particles was less than threshold limit value.