Effects of Long-Term Occupational Silica Exposure on Pulmonary Function Tests in Fire Brick Workers


1 Department of Pulmonary Medicine, Isfahan University of Medical Sciences,

2 Department of Internal Medicine, Shahrekord University of Medical Sciences, ISFAHAN-IRAN


Background: Pulmonary function decreases by advancing age in adults. Its results decrease in volume and airflow in spirometry. This decrement accentuates with cigarette smoking and occupational exposure to noxious materials including silica. Silica is known for its fibrosing effect on lung, but its effect on airways is questionable. Materials and Methods: Seventy six of the 151 total workers of a fire brick factory with mild silica exposure were followed for six years by repeating pulmonary function tests each two years. Spirometric parameters including: forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), forced expiratory flow at 75% of expiration (FEF75), and forced midexpiratory flow (FEF25-75) were recorded in each follow-up. The data were analyzed using paired sample t-test. The differences between each succeeding measurement and the original first one were calculated. Results: The subjects age ranged from 28 to 60 years, (mean±SD=39.9±7.71), and mean time of their employment was 13.7±5.23. Only 23.6% of them were smokers. During the study period the measured values for spirometric parameters were steadily decreasing. Mean annual decrements for FVC, FEV1, FEF75, and FEF25-75 were 49.84, 61.95, 31.5 and 148.8 ml, respectively. All of these values were much more than normal limits. Conclusion: Exposure to silica dust amounts is insufficient to produce pulmonary fibrosis, but it can result in chronic obstructive pulmonary disease as reflected in aggravated reduction of expiratory flow rates in workers participated in this study. (Tanaffos 2003; 2(5): 23-28)