To improve mine health and safety conditions, there is need for a portable instrument that mine inspectors can use routinely for rapidly checking concentrations of dust in mine atmospheres. The prime objective of this study was to build, calibrate, and deliver to the Bureau of Mines two prototype instruments based on a design previously developed. The emphasis was to be on providing instruments which would meet certain minimum standards of size, weight, response time, sensitivity, ruggedness, reproducibility, permissibility, and cost (ultimate); optimization of the design was to be considered only insofar as it would not significantly delay the development. One instrument was to be delivered after initial calibration of both instruments with coal dust pgh. The second instrument was to be used for further calibration with a number of other coal and rock dusts and for assessing other relevant performance characteristics. This report summarizes the results of this study.