Dust formation by impact machines, roof supports and shotfiring and its relationship to mining and geological factors. Final report on CEC Contract 7253-46/8/087

An investigation into the influence on coalface dust dispersion of chock-moving, shotfiring and impact ripping was carried out at a number of British coalmines by investigators from the Institute of Occupational Medicine. This was a sequel to an earlier investigation by the same group into dust formation and dispersion by the main coal-winning machines.The faces used in the exercise, many with specific problems to be tackled during the investigation, were from the full range of coal seams and mining conditions. The measuring techniques required the use of the SIMSLIN Ib light scattering instrument in addition to the customary measuring instrument in UK mines, the MRE Gravimetric Sampler, Type 113A. An instrument was constructed specially for the collection of dusts for size and compositional analysis to help in determining the origin of some dusts.The observations revealed that there was a considerable contribution to face dust from both chock-moving and shotfiring. Although dust produced locally by chocking was generally coarse and regarded as “”nuisance”” its contribution to the 70 m control point respirable concentration could be, in certain conditions, up to 30 per cent. Higher dust concentrations were found during chock-moving under coal roofs (compared with stone roofs) and in the thicker seams. Moreover the face workforce was more likely to be exposed to this dust than to that from coal-cutting which tended to plume down the face-track.Although produced in bursts of short duration, shotfiring dust also contributed considerably, up to 2 mg/m on occasions, to the control point (70m) concentration. There was a clear relationship between explosive utilisation and dust produced by shotfiring, except when firing in solid strata because, in these conditions, the debris and shotfiring dust were not exposed to the full ventilation stream.Impact rippers were found to produce less dust than rotary rippers, which tend to be used in harder strata, or conventional methods which involve shotfiring. “”