Radon and thoron daughter working levels in British coalmines

Underground radon and thoron daughter activity levels have been determined at 11 collieries. The method used was that previously developed by the Institute of Occupational Medicine to measure the activities of daughter products attached to coalmine dust particles collected with the intrinsically safe MRE Gravimetric Sampler, Type 113A.Activity levels in the collieries investigated are low compared with those typical for uranium mines. At ten of the collieries total measured activities were below 20 mWL per shift. At the other colliery rather higher activities were observed, the values ranging from about 13 to 40 mWL on the coalface, though higher values (c. 65 mWL) occurred at the furthermost point in the ventilation stream.The effects of several factors on radioactivity levels were examined. These included weight and particle size range of dust, atmospheric pressure, coal rank and ventilation distance. It is concluded that, of these factors, only ventilation distance has an important influence on the activity levels.The limited data available from this study on the temporal and spatial variations in activity levels are presented and discussed :in relation to environmental factors.