THE MINERALOGY AND SIZE OF AIRBORNE CHRYSOTILE AND ROCK FRAGMENTS: RAMIFICATIONS OF USING THE NIOSH 7400 METHOD

Abstract

The length and width of chrysotile and rock fragments that were collected on nine air-monitoring filters in the mine and plant of the Lowell asbestos mine in Vermont have been measured by transmission electron microscopy (TEM). Selective area electron diffraction (SAED) and energy dispersive x-ray analysis (EDS) were used to identify particles longer than 5 µim with a length-to-width aspect ratio of at least 3:1 (federal fiber). All federal fibers were found to be chrysotile or serpentinite rock fragment; no tremolite or other amphiboles were detected. Magnifications of400× and 19 OOO× were used on five filters in an attempt to compare the size distributions of the federal fibers likely to be measured by using phase contrast optical microscopy (PCM) at 400× to those measured by TEM at higher magnification. The data from the mine show that (1) the size distribution of chrysotile determined at 19 OOO× differs substantially from that determined at 400× but the size distribution of rock fragment is nearly ind...