National Institute for Occupational Safety and Health

“ Other fibers with optical properties similar to the asbestos minerals may give positive interferences. Optical properties of asbestos may be obscured by coating on the fibers. Fibers finer than the resolving power of the microscope (ca. 0.3 μm) will not be detected. Heat and acid treatment may alter the index of refraction of asbestos and change its color. ”

“ Prepare a slide in 1.700 RI liquid. Examine under plane-polarized light (uncrossed polars) ; check for morphology of crocidolite. Fibers will be straight, with rigid appearance, and may appear blue or purple-blue. Crocidolite is pleochroic, i.e., it will appear to change its color (blue or gray) as it is rotated through plane polarized light. Insert the dispersion staining objective. The central stop dispersion staining color are red magenta and blue magenta, however, these colors are sometimes difficult to impossible to see because of the opacity of the dark blue fibers. ”

“ Mix the fibers and particles on the slide so that they are as homogeneous as possible. NOTE: An even dispersion of sample should cover the entire area under the cover slip. some practice will be necessary to judge the right amount of material to place on the slide. Too little sample may not give sufficient information and too much sample cannot be easily analyzed. ”

“ If anisotropic fibers are found, rotate the stage to determine the angle of extinction. Except for tremolite-actinolite asbestos which has oblique extinction at 10-20E, the other forms of asbestos exhibit parallel extinction (Table 1) . Tremolite may show both parallel and oblique extinction. d. Insert the first order red compensator plate in the microscope and determine the sign of elongation. All forms of asbestos have a positive sign of elongation except for crocidolite. If the sign of elongation observed is negative, go to step "g." ”

“ Ventilated hood or negative-pressure glove box. 6. Mortar and pestle: agate or porcelain. 7. Stereomicroscope, ca. 10 to 45X. 8. Light source: incandescent or fluorescent. 9. Tweezers, dissecting needles, spatulas, probes, and scalpels. 10. ”