Dust formation in relation to mining and geological factors. Final report on CEC Contract 6253-46/8/017

An investigation of mining and geological factors likely to influence dust production and dispersion was carried out at a number of British coalmines by investigators from the Institute of Occupational Medicine along with their routine environmental measurements on coal faces for the Pneunoconiosis Field Research.The measurement indices used in the study were dust concentration (quantity of respirable dust in unit volume of ventilation air), dust production (quantity of respirable dust liberated in unit time) and dust dispersion (quantity of respirable dust liberated per tonne of coal cut).One of the noteworthy points in the investigation was the great variability of the measurement indices which made difficult the controlled examination of parameters affecting dust production and dispersion. Observations revealed that the amount of dust arising from mining operations was greatly influenced by geological irregularities such as faulting of the coal seam and, in thinner seams, through excursions by the cutting machine into the surrounding strata, particularly the floor; this was a practice not always necessary or justified. On the other hand, cutting dirt bands which is unavoidable had relatively little effect on dust production and it was thought that the scraping action of the pick at floor and roof level as compared with the deeper penetration at mid-seam was an important factor in making dust. For these reasons dust production was frequently related inversely to the amount of coal produced.A high proportion of coal from British mines is now produced by shearer. Work carried out in 1964 had shown dust dispersion by this type of machine to be related inversely to haulage speed but directly to the frequency of pick attack. At the time particle counts formed the basis of the measurement indices so it was of interest that the earlier findings should be confirmed by the present study, using mainly gravimetric measurements. However, these variants of machine dust production may have been, simply, further cianifestations of the effect of difficult mining conditions. Possibly also of significance in shearer operation were the observations that dust production increased when the drum was not fully buried in the coal and that re-cycling of previously cut material led to higher dust dispersion.The pattern of dust production was markedly different in the high rank coals which are normally thicker and where cutting was, thus, almost entirely within the coal itself; one very special feature was the generation of relatively high dust concentrations through releasing crushed roof coal during chock moving. Dust raised by the machine was considerably coarser than in the lower rank coals and contained much less non-coal.Cutting non-coal mineral produced finer dust and relatively more than did cutting coal (approximately 50 and 1000 times as much for cutting floor and fault respectively) with consequent influence en the dust cloud; for example, the brea!:-up of coarse quartz grains while cutting sandstones led to high quartz representation. Such observations relating to the quality of the dust were unavoidably limited anil leave scope for further vrork on this aspect of dust production.One of the factors not directly connected with the cutting machine but nevertheless affecting dust dispersion was ventilation. It v:as found that increasing both quantity and velocity apparently reduced dispersion. Other non-mechanical factors which might influence dust production and dispersion such as coal rank, inherent moisture of the coal and dust suppression water all require closer examination in better controlled conditions than could be provided by a programme of routine dust measurement.Other face operations besides coal cutting, such as those at roadheads, ‘contribute appreciably to dust production and merit special investigation.The need for a short-period gravimetric dust sampler for use in future investigations of this nature is noted.