When might TEM be used as a double check in PLM analysis of asbestos samples?

When might TEM be used as a double check in PLM analysis of asbestos samples?

• A. Only for positive PLM results.
• B. When fibers are extremely narrow and PLM results are negative.
• C. TEM is never used as a check.
• D. TEM should replace PLM.

Answer: (B)

The main idea is that polarized light microscopy (PLM) has limited ability to detect and positively identify asbestos fibers when they are extremely small. Transmission electron microscopy (TEM) offers much higher magnification and resolution and can image submicron fibers, plus it can provide diffraction and elemental analysis to confirm asbestos type. Because of this, TEM is used as a confirmatory check when PLM results are negative but there is still suspicion of asbestos, especially if fibers are extremely narrow and may escape PLM detection. TEM complements PLM rather than replacing it; it’s not routine for positive PLM results, and it’s not used as a universal replacement for PLM.

The main idea is that polarized light microscopy (PLM) has limited ability to detect and positively identify asbestos fibers when they are extremely small. Transmission electron microscopy (TEM) offers much higher magnification and resolution and can image submicron fibers, plus it can provide diffraction and elemental analysis to confirm asbestos type. Because of this, TEM is used as a confirmatory check when PLM results are negative but there is still suspicion of asbestos, especially if fibers are extremely narrow and may escape PLM detection. TEM complements PLM rather than replacing it; it’s not routine for positive PLM results, and it’s not used as a universal replacement for PLM.