Abstract
Nine steel workers participated in controlled exposures to sulphur dioxide alone and sulphur dioxide plus carbon dust (5 ppm and 10 mg/m3, respectively). All were experiencing work related respiratory difficulties. Bronchial clearance was measured using radioaerosol inhalations and external detection. Results were variable and no statistically significant changes were observed. One asthmatic showed a complete cessation of clearance during exposure to sulphur dioxide and carbon dust. Bronchial reactivity was found to be significantly raised after exposure to sulphur dioxide but equivocal results were found after exposure to sulphur dioxide and carbon dust. Pronounced changes in pulmonary function were seen only in the two asthmatic subjects. They could not tolerate the levels, indicating that these threshold limit values are too high, at least for these individuals who showed much greater sensitivity to the pollutants than the others.