MEASUREMENT OF AIRBORNE MINERAL FIBERS 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 evalu ation of the azimuthal light scattering pattern generated by single pa rticles which are illuminated by circularly polarized laser light. The instrument uses eight different optical detectors placed at a polar a ngle of 55 degrees and in an azimuthal angular regime from 69 degrees to 90 degrees. The variability in the azimuthal light scattering patte rn can be used to measure the fibre length whereas the fibre diameter can be derived from the intensity averaged over the corresponding valu es of the eight detectors. Detector responses are calculated on the ba sis oi the boundary value method (van de Hulst solution) in order to s how the theoretical resolving power of the instrument with respect to size and length. Measured data from polystyrene latex spheres (PSL), s odium chloride particles, quartz particles and glass fibres are presen ted. The differently shaped particle types were used to demonstrate th e ability of the instrument in distinguishing between fibrous and nonf ibrous particles. The evaluation of fibre diameter and length from mea sured values using calculated calibration data is shown for several sa mples.