Airborne coalmine dust and chronic bronchitis.

The prevalence of chronic bronchitis was compared in a group of 970 coalminers and in 538 controls by means of a standardized questionnaire and of VC and FEV1 measurements. The coaldust present in the galleries had a low content of free silica and the dust levels were lower than the maximal permissible concentrations with reference to the US standards. The socio-economic characteristics, and mean height values were identical in both groups. The controls were somewhat older than concerning bronchitis symptoms were found in the non-smokers. The non-smokers exposed to coaldust showed higher prevalences of cough and FEV1 abnormalities than their matched controls. The unfavourable effect of exposure to coaldust on the bronchi was masked by cigarette smoking.