A comparative assessment of dust surveillance procedures including the use of personal and fixed position sampling instruments. Final report on CEC Contract 6253-21/8/015. on CEC Contract 6253-21/8/015.

A comparative assessment of dust surveillance procedures on longwall coalfaces was carried out by the environmental field staff of the Institute of Occupational Medicine. The object of the research was to provide the essential data on which future dust surveillance schemes might be founded rather than the propounding of a particular system.The basic data for the research included routine dust measurements made by the Pneumoconiosis Field Research in their underground investigations at ten British collieries for the purpose of providing exposure records to compare with pneumoconiosis risk. These measurements were made usually for the whole time underground, including travel, by workmen carrying “”fixed point”” gravimetric samplers to their working locations but additional measurements were made at the 70m statutory control sampling point (UK collieries) during the face working period only, so that the effectiveness of locating the control point in the return roadway could be examined. Personal samplers were also distributed on occasions to members of working groups so that the relationship between “”personal”” and “”fixed point”” samples could be established. Personal samplers also provided information on local variability of dust conditions.Fixed point sampling showed consistent differences in mean dustiness between collieries; variability was of similar order of magnitude (coefficient of variation c 30 per cent) to that between faces within a colliery. The general pattern of dustiness established was of relatively low concentrations at intake ends of coalfaces approximately doubling in transit to the return. Face-line samples gave a good estimate of man-weighted face mean concentrations. A number of factors were found to modify this general pattern.The numerical value of the ratio of control point to coalface mean concentrations, 1.4 was found not to have altered greatly since 1970, although the location of the control point had been moved from 25yd to 70m along the return roadway since the ratio was first evaluated. Evidence now suggests that the present location is the optimum for the return roadway control point. The factor most likely to alter this ratio was found to be homotropal ventilation. On average, 16 per cent of concentrations recorded on the coalface exceeded those at control points which suggests a need for the type of investigation provided by personal samplers at special points on the coalface. When comparing personal and static sampler concentrations, there was little to choose between the instruments, both showing similarly representative concentrations.Although personal samplers gave concentrations on average about 10 per cent higher than static samplers the validity of the rationale behind the control level in UK mines, based on static sampling, is not in question. There were indications that static samplers had underestimated concentrations at the intake ends of faces in the past by approximately 40 per cent and this could alter the accepted pattern of face concentrations.Personal samplers were also used to examine the homogeneity of exposures experienced by individuals in working groups. Variability between members of a group was only high when the group was spread along the face-line; within these groups there was no indication that machine operators might be more at risk than proppers or conveyor movers.Temporal variations in dust concentration were studied. Short-term, variability increased directly with concentration suggesting the need to concentrate sampling effort near the return end of the face where concentrations are highest. There also appeared to be some bias related to day of the week, on which the sample was taken concentrations being lowest on Mondays and Fridays. In the longer term, variability appeared to be higher at the control point than on the face. The optimum interval between groups of samples for the purpose of dust control appeared to be of the order of one month, but for the purpose of estimating exposures some type of running mean appeared preferable.Variations in individual dust exposure were examined and were found to be influenced by local patterns of working and attendance. It was found that there were few “”pure”” faceworkers since almost all had spent some time on non-coalface operations. There was little evidence of exposures being averaged through movement between intake and return ends of faces; some individuals appeared to be specifically associated with the dusty areas.Colliery face concentrations did not reflect accurately individual exposure levels which were lower than expected. Some past exposure levels may have been overestimated. “”