Size classification of fibers and isometric particles keeping each fraction airborne

The hazardous properties of airborne fibers are generally thought to be related to size. The purpose of this study was to develop a technique for physically classifying airborne fibers on the basis of diameter, keeping the separated fractions in the suspended state. This would permit either fraction to be further classified, monitored by real-time instrumentation and/or used in size-related inhalation studies. Other fiber classification methods have involved deposition of fibers onto a substrate, which precludes these advantages. Diameter classification was achieved by the use of an opposing-jet aerosol classifier. With isometric aerosols, sharp diameter classification was achieved: D50/D16 = 1.1 for liquid particles, and D50/D16 = 1.3 for solid particles. Diameter classification of fibers was also achieved, but the sharpness of cut was much less; D50/D16 greater than 3. The decreased sharpness of cut for fibers is attributed to the more or less random bounce of fibers from the edge of the separation plate to either outlet flow of the classifier. The sharpness of cut is expected to be better in a classifier in which the thickness of the separation plate is smaller relative to the flow dimensions.