Respiratory morbidity among processing and mill workers. A cross-sectional survey in three tire-manufacturing plants

Three hundred seventy workers in three tire-manufacturing plants were studied to determine the presence of respiratory morbidity among workers with relatively low current exposure to respirable dust (range, 0.04 to 0.70 mg/m3). Workers in the processing, milling, and less dusty areas of the plants were divided into three groups on the basis of their current and past exposure to respirable dust. Significantly more eye irritation (p less than .01) was found among workers in the milling areas. Workers in the milling areas who were current cigarette smokers had significantly (p less than .05) more chronic bronchitis and loose or productive objective cough than all other current cigarette smokers. The mean forced expiratory volume in 1 s (FEV1), when corrected for age and height, decreased significantly (p less than .01) with increasing duration of cigarette smoking. The mean FEV1 and the forced vital capacity (FVC), when corrected for age, height and cigarette smoking, were the lowest in the group with the lowest dust exposure and highest in the group with moderate dust exposure (the milling areas). The measurement of the difference in flow at 50% of FVC on air and on a helium-oxygen mixture is a sensitive test for small-airway obstruction in the laboratory. In the field, however, the helium-oxygen flow difference did not vary with duration of cigarette smoking as expected, and there was no significant variation by exposure category.