A method for measuring the potential alpha (working-level values) of airborne radioactivity in coalmines

Following findings that airborne radioactivity could reach potentially dangerous levels in metal mines a method has been developed and tested for measuring the hazard in working levels due to low airborne concentrations of mixed radon and thoron daughters in coalmines,, The measurement is made on a sample of respirable dust collected throughout a shift. The alpha-decay of the sample is measured for two periods, the second ending four hours after the end of sampling, and the working-level values of the two radioactive series are obtained. The method is sensitive to 1 mWL or less, and the figures are a reasonably accurate measure of the average exposure of the worker through the shift. The sampling equipment used is the MRE gravimetric sampler, which is electrically safe in a methane-air mixture. Field trials in a colliery over a period of eight months show:(1) no secular change of total working levels} (2) random variation withtime within 30% of the mean. (3) no difference between the working levels given by total and respirable dust samples; (4) little, if any, variation between different faces in the same seam; (5) little, if any,variation with barometric pressure; (6) an average face workings-levelvalue of about 25 mwL, about 70% of this being the radon compoment. The method is now being used to survey the airborne radioactivity hazard in British coalmines. “”