The variability of exposure of coalminers to inspirable dust

The project sets out to provide information about the variability of exposure of coalminers to fractions of airborne dust containing particles that are coarser than those contained within the respirable subfraction. This is to enable progress to be made in epidemiological research studies relating exposure to various dust subfractions and the incidence of upper airways disease.The philosophy adopted for the choice of dust sampling instrument used for this investigation was that it should simulate the nature of human dust exposure for all relevant particle sizes. This includes sampling of ‘total’ airborne dust according to the definition of inspirable particles (i.e., those which may enter through the nose and/or mouth during breathing) and the subsequent selection of biologically-relevant subfractions representing deposition of particles in the various anatomical regions of the respiratory tract. The question arises: can a reliable measurement of the individual exposure of a coalminer to inspirable dust be obtained by using a static sampler, or should a properly-designed personal sampler be used? Also: what are the relationships between inspirable dust and the various subfractions referred to (e.g., thoracic, tracheobronchial, respirable)? The main objective of the project was to provide answers to these questions.Before any underground sampling could take place, appropriate sampling instrumentation – consistent with the above criteria – had to be obtained. To begin with, a static inspirable dust sampler was already available, based on previous work at the Institute of Occupational Medicine, and it was considered suitable for measurements in the general workplace atmosphere. As far as the more specific measurement of individual work exposure is concerned, the suitability of a number of existing instruments was examined. To this end, the sampling performances of three personal samplers commonly used in British industry workplaces for sampling ‘total’ dust were evaluated in the wind tunnel, to see if any of these would be suitable. The tests were carried out with the samplers mounted on a life-size mannequin to simulate the manner in which they would be used in reality. Since neither of the three samplers turned out to be satisfactory for the required task, the development of a new device was carried out. The result was a small personal sampler characterised by its 15 mm circular entry which, when worn on the lapel and operated at a sampling flowrate of 2 1/min, collects the inspirable fraction over a wide range of dust particle sizes and wind speeds relevant to coalmine conditions. In addition to this personal sampler for inspirable dust, a modified version was also developed which not only samples the inspirable fraction but also provides information about the particle aerodynamic size distribution of that fraction. From such information, it is possible to determine the size distribution of and mass contained within any subfraction that can be defined numerically (including those already referred to).In the underground trials, the static and personal samplers referred to were employed in three different collieries chosen to represent a range of current mining methods and conditions in British coalmines. The major feature of the design of the trials involved division of the workforce into occupational groups whose jobs,working sites and – perhaps – their dust exposures were similar. Repeatmeasurements were made of the exposures of the men within each occupational group to inspirable dust and the various dust subfractions. “”