Investigations into the distribution of dust concentrations in the face area

The distribution of dust concentrations in the face area has been studied at the ten PFR collieries to provide background information relevant to a review of the interim gravimetric dust standards and the strategy of dust surveillance in British coal mines. Preliminary experience with the Simpeds personal sampler in comparison with the MRE hand-carried sampling instrument is also reported.The principal findings were as follows :-(i) The previously observed factor of 1.4 – used in deriving the interim standard of 8 mg/m3 – between dust concentrations at the control point in the return roadway and the colliery mean coalface concentration (which had in turn been related to the pneumoconiosis risk) remains valid on average for the ten PFR collieries. It has not been tested outside those collieries, but they were chosen to be representative and have been found so in various other respects.(ii) There are substantial departures from this average ratio at individual collieries, and even greater departures on individual faces. It is not yet known to what extent these differences are random and will tend to average-out in the long term,/ term, but some factors which consistently bias the ratio have been noted, e.g. homotropal ventilation.(iii) Overall, there has been little change in the collierymean coalface concentrations at the 10 retained PFR collieries from 1967 to 1971.(iv) Overlapping measurements by Production Department and PFR at face return control points in the PFR collieries differ on average by 12 per cent. There are larger differences in individual cases.(v) There is a loss of dust between the 25 yd and 70 m control sampling points in return roadways, but the change in sampling position does not appear to have affected the mean control point/face concentration ratio because of the effects of other procedural changes. Concentrations near the roof or side of the return roadways are generally lower than at the centre. It is recommended that control samples should be taken near the centre of the roadway.(vi) Dust concentrations at the 70 m control point are often exceeded (in the long term average as well as on individual shifts) elsewhere on the face, particularly in return stable holes.(vii) Side by side trials of early prototype models of the SIMPEDS personal sampler and MRS samplers showed that the ratio of the measured dust concentrations varied from colliery to colliery. Further studies are recommended when the design of the SIMPEDS has been finalised and production models are available.(viii) A comparison of concentrations measured by worn SIMPEDS and by a similar instrument carried by the same workman and placed statically near his place of work (in the way that MRE samplers are used in the ordinary PFR studies) showed reasonable agreement on average but substantial differences in individual cases. “”