COMPUTER SIMULATION OF PARTICLE OVERLAP IN FIBER COUNT SAMPLES
Resource
AIHAJ v.62 n.3 pp.281-287
Journal
AIHAJ
Journal Volume
v.62
Journal Issue
n.3
Pages
281-287
Date Issued
2001
Date
2001
Author(s)
CHEN, CHIH-CHIEH
Abstract
Fibrous aerosols are of great importance to industrial
hygienists because of the severe health risks that may be
associated with inhaling such particles. Previous studies on
measurement error due to overloading of fibers and
nonfibrous particles on the collected sample indicate that a
100-1300 fiber/mm(2) filter area is the best filter loading
density to reduce bias in fiber counts. The present study
investigated the upper fiber and particle concentration
limits for reliable counting and identification and the
possibility of a procedure for correcting observed fiber
counts to account for fiber masking due to overlapping
particles or fibers. A computer-generated grid was used to
simulate the light microscope graticule field. The
resolution of 2000 x 2000 was found to accurately represent
the shape of the fibers and nonfibrous particles. Bivariate
lognormal distributions were used to describe the length and
width distributions of the fibers. The capability of
distinguishing particle-overlapped fibers (defined as the
resolution index), the coverage of the graticule field, the
filter surface loading density, size distributions of fibers
and particles, and the fiber-to-particle concentration
ratio were the primary parameters in this study. The
counting efficiency was found to consistently decrease with
increasing filter surface loading density and decreasing
resolution index. The recommended upper limit of filter
surface fiber density depended not only on the number
concentration ratio but also on the filter surface loading
densities and size distributions of fibers and particles.
The advantage of using a thoracic preseparator on counting
efficiency was calculated and found to improve counting
efficiency significantly when the count median diameter of
nonfibrous particles was close to or larger than the
thoracic 50% cutoff point of 10 mum.
Subjects
fiber counting
fibrous aerosols
thoracic preseparator
SDGs
Type
journal article