 Five bulk building materials have been categorized by EPA that
are very difficult to analyze by polarized light microscopy (PLM).
EPA recommends these materials be analyzed by transmission
electron microscopy (TEM). (EPA 600/R-93/116 Appendix D)
“Analysis by TEM is capable of providing positive identification
of asbestos types and semi-quantitation of asbestos content.”
PLM Point Counting methodology is not recommended for these
materials.
False negative results for vinyl asbestos floor tile are
typically 20-30%.
New York State Department of Health requires tiles found negative
by PLM to be reanalyzed by TEM.
These materials are dominantly nonfriable and fall into the
following categories:
- Cementitious Products (pipe, sheeting, etc.)
- Viscous Matrix Products (adhesives, cements, coatings, etc.)
- Vinyl Material (vinyl floor tile, sheeting)
- Asphaltic Roofing Materials (shingles, roll roofing)
- Miscellaneous Products (paints, coatings, friction plates, gaskets, etc.)
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Note the obvious fiber bundles of chrysotile asbestos (Fig.1), the lack of fiber bundles in floor tile (Fig.2) and obvious fibers of chrysotile by TEM (Fig. 3). Over 20% of NVLAP laboratories reported this tile as negative (Figs. 2 & 3).
Figure 1
CH Asbestos
Scope Mag. 100x
Dispersion Staining
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Figure 2
Vinyl Asbestos Tile
PLM
Scope Mag. 100x
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Figure 3
Vinyl Asbestos Tile
TEM
Scope Mag. 13,000x
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