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Evaluation of the phase contrast microscopy method for the detection of fibrous and other elongated mineral particulates by comparison with a stem technique.

Snyder JG; Virta RL; Segreti JM
Am Ind Hyg Assoc J 1987 May; 48(5):471-477
The efficiency of the phase contrast microscopy (PCM) method for the detection of mineral particulates was investigated by comparing it to a technique employing scanning transmission electron microscopy (STEM), which has a typical resolution of less than 5 angstroms. Seventeen personal air monitor filters from workers with possible asbestos (1332214) exposures were obtained and characterized initially by STEM with the use of energy dispersive X-ray analysis on a particle by particle basis. In the analysis of total fibers, PCM did not detect all mineral fibers adequately. STEM/PCM particle count ratios indicated that a significant number of particles were missed by PCM in each sample, particularly in samples containing chrysotile (12001295). For amphibole cleavage fragment samples from mining sites, the PCM was adequate since no regulatory particles (length of 5 microns or greater and aspect ratio of 3:1) were below the resolution of the optical microscope. For amosite (12172735) and chrysotile samples from occupational sites and chrysotile samples from mining sites, approximately one third of the regulatory particles were below the resolution of the optical microscope. Exceptions were found for air monitor samples containing many thin particles. The authors note that many chrysotile particles observed by PCM are comprised of hundreds of individual fibrils when observed by STEM or TEM. Therefore regulation of chrysotile should include analysis by STEM or TEM. They also recommend a direct transfer technique for sample preparation so that the original particle concentration and size distribution is not altered. Multiplication factors of 1.5 for chrysotile and amosite and 1 for amphibole are suggested for use with PCM counts in order to obtain a more accurate assessment of particle counts.
Mining-industry; Air-sampling-equipment; Air-quality-monitoring; Air-filters; Particulate-dust; Particulate-sampling-methods; Microscopic-analysis; Mineral-dusts; Airborne-dusts; Asbestos-fibers; Airborne-particles; Air-monitoring; Analytical-methods; Asbestos-dust
12172-73-5; 1332-21-4; 12001-29-5
Publication Date
Document Type
Journal Article
Fiscal Year
Identifying No.
OP 30-89
Issue of Publication
NIOSH Division
Source Name
American Industrial Hygiene Association Journal
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division