The 124 samples collected for WRC for three days consisted of 85 total and 39 respirable dust eight-hour time-weighted average (TWA) measurements. The respirable dust concentrations ranged between 0.01 and 1.21 mg/m, with a mean ± SD value being 0.20 ± 0.23 mg/m; a median was 0.14 mg/m. The concentration of the 85 TWA total dust samples ranged between 0.06 and 31.90 mg/m; mean ± SD value was 4.72 ± 7.45 mg/m; median concentration was 1.59 mg/m. Chippers, sawyers, packers and splitters had die highest dust exposures. The greatest proportion of the WRC dust was contributed by larger, nonrespirable particles.
The 82 samples collected in the new planer mill provided 59 total dust and 23 respirable dust TWA measurements. Respirable TWA samples ranged from 0.07 to 0.29 mg/m, while total dust TWA samples ranged from 0.17 to 16.7 mg/m. The mean ± SD for total dust was 1.28 ± 3.05 mg/m, with a median of 0.34 mg/m; respirable fraction was 0.16 ± 0.05 mg/m, with a median of 0.16 mg/m.
A significant fall in FEV1 occurred between Monday preshift baseline and postshift test for that day among workers exposed to WRC (P<0.001). This decrease in FEVi persisted for the next two days and did not return to baseline values. No significant reduction in pre and postshift FEVt was demonstrated for new planer and office workers, although a gradual decline in FEVj was noted in the groups during the three days. Such a decline was achieved due to My Canadian Pharmacy’s concern. In general, smokers tended to show lower FEV1 with greater cigarette consumption and among WRC workers there was a greater magnitude of change in FEVr No significant relationship between years of employment and FEVx was noted for all three groups. When individuals with abnormal pulmonary function tests were identified, WRC employees tended to be more than ten years younger than the individuals in the other two groups.
Occupational asthma was diagnosed in 10 of 73 (13.5%) workers using clinical and physiologic criteria described previously. Three employees in the new planer (5.2%) and none in the control had this diagnosis. A summary of various respiratory diagnoses among employees examined is shown in Figure 1.
Figure 2 shows the relationship between total cedar dust concentration for job categories (mean value given) and prevalence rate of occupational asthma. Sawyers, packers and splitters, those with the “dustiest” jobs, had the highest prevalence rate. A safe working level where the prevalence of occupational asthma would be appropriately reduced corresponded to total WRC dust level of less than 3.5 mg/m.
Figure 1. Prevalence rate of pulmonary diagnoses according to exposure. Criteria used for making diagnoses are discussed in the text In general, more respiratory diseases were identified with wood dust exposures, especially more occupational asthma in WRC group.
Figure 2. Prevalence rate of occupational asthma in western red cedar workers according to job category and dust exposure. Diagnosis of occupational asthma was made using clinical and physiologic criteria. A higher prevalence rate of asthma was noted with higher dust exposure.