Relationship Between Concentrations of Respirable Dust at Points 25 yards and 70 metres from the Coalface

Changes in the approval conditions for airborne dust which came into effect at April 1970 have resulted in the control sampling point for longwall faces in coalmines being removed further from the face to a point 70 m along the return roadway.As the research leading up to the present control limit of 8 mg/m3 was carried out at the former control point located at a distance of 25 yd from the face, it was necessary to examine and evaluate the effect of the change of sampling point on the measurement of dust concentrations. The 85 pairs of observations on 23 faces at 10 collieries covering a variety of environmental conditions show that the move to 70 m effectively reduces dust concentrations by, on average, 13 per cent.The reasons for the reduction in concentration are examined and the links with coal rank, ventilation velocity and roadway height are explored. Further work to establish the importance of other factors, such as size-distribution of the dust, is proposed.