Measurement of airborne mineral fibres using a new differential light scattering device

A new light scattering instrument is described for the measurement of airborne mineral fibres. The measuring principle is based on the evaluation of the azimuthal light scattering pattern generated by single particles which are illuminated by circularly polarized laser light. The instrument uses eight different optical detectors placed at a polar angle of 55 degrees and in an azimuthal angular regime from 69 degrees to 90 degrees. The variability in the azimuthal light scattering pattern can be used to measure the fibre length whereas the fibre diameter can be derived from the intensity averaged over the corresponding values of the eight detectors. Detector responses are calculated on the basis of the boundary value method (van de Hulst solution) in order to show the theoretical resolving power of the instrument with respect to size and length. Measured data from polystyrene latex spheres (PSL), sodium chloride particles, quartz particles and glass fibres are presented. The differently shaped particle types were used to demonstrate the ability of the instrument in distinguishing between fibrous and nonfibrous particles. The evaluation of fibre diameter and length from measured values using calculated calibration data is shown for several samples.