± 1.6 × × × × × 10 -2 mg/m 3 respectively, which belonged to the exposure of the workers of hammer drill process. The prevalence of skin and respiratory symptoms were higher in hammer drill workers, however, respiratory symptoms showed no significant prevalence. Regarding the average age of workers (31.6 ± 1.9 yr) and average of their work history (3.8 ± 1.0 yr), these results were predictable.