The measurement of air-borne ‘fly-dust’ in mines. Final report on CEC Contract 6253-21/8/068

Fly-dust has been defined as airborne coarse dust which can causo irritation on impact with the skin or the eyes. It is known to be a problem to underground workers at some locations in some coal mines. For example, one source of “”fly-dust”” at the coal face arises from the movement of powered roof supports.Laboratory experiments on human subjects, based on classical psychophysical methods, show that the threshold for a given level of sensation due to impacting dust on the facial skin of a given subject follows a unique relationship between dust (mass) concentration and Stokes number (for particle movement in the air about the head). This is consistent with a theory based on “”impaction pressure””.Experiments with human subjects exposed to “”fly-dust”” in coal mines showed that there is an upper limit on particle size entering the eye, governed by the protective blinking mechanism of the living eye and dependent on the mode of dust dispersal at source, its size distribution, concentration and Stokes number.The “”fly-dust”” problem thus functionally characterised, a device has been developed which can acquire the basic information required for its measurement in an appropriate functional form. The active element of this device is a bimorph piezoelectric transducer, onto which the “”fly-dust”” impacts. Ultimately this device can be incorporated into an electronic instrumentation package for “”fly-dust”” measurement, calibrating its response against the known responses of by appropriate processor design. “”