Construction of a portable fiber monitor measuring the differential light scattering from aligned fibers

Abstract

This report describes experimental work in which three separate physical techniques have been combined to produce a portable monitor for airborne fibers. Air containing the fibers to be monitored is drawn through a rectangular, slotted inlet into the instrument at 4 L/min using a battery pump. The flow acceleration at this inlet aligns the fibers. Corona charging then enables the fibers to be precipitated onto a standard microscope slide while retaining their alignment. The difference in light scattering along and at right angles to this deposit is used to determine the concentration of fibers. Calibration of the instrument is achieved by counting the fibers on the slide by phase-contrast optical microscopy for a range of concentrations. A backup filter traps any fibers that escape the corona charging and precipitation region, and this filter can be analyzed by electron microscopy so that the fibers can be identified. Performance data are presented for fibers and compact particles sampled from a laboratory dust box, and for the angular dependence of light scattering from these deposits, measured directly from the slide, to demonstrate optimum detector geometry. © 1992 Elseiver Science Publishing Co., Inc.