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An optical particle counter has been calibrated for size distribution measurement of airborne coal dust particles. A differential electrical mobility analyzer was used with a fluidized bed dust feeder to produce uniform coal dust particles of a known size for calibration for particles <2.4 μm. For larger particles, the optical counter was calibrated with a microscopic technique. The output pulse height of the optical counter was found to be significantly lower for coal particles than for spherical oil drops of the same particle size. The geometrical standard deviation, σg, of the output pulse height distribution of the optical counter for monodisperse aerosols was found to increase from about 1.1 for spherical oil particles to about 1.8 for the irregularly shaped coal particles. Although this broadening effect reduced the ability of the counter to resolve small particle size differences, a numerical inversion procedure was developed which allowed the original size distribution to be recovered.

A system for sampling aerosols in the facepiece of a powered air purifying respirator has been described. The system consists of a sampling inlet mounted on the respirator facepiece, a filter cassette and a personal sampling pump. The theoretical and practical considerations leading to the design of the sampling inlet have been discussed and experimental data presented showing the efficiency of the inlet as a function of particle size and sampling flow rate. The in-mask sampling system has been designed for powered air purifying respirators.