Which materials might PLM miss due to extremely narrow fibers?

• A. Drywall
• B. Nonfriable materials such as floor tile or plaster.
• C. Glass
• D. Wood

Answer: (B)

Polarized light microscopy can miss very fine asbestos fibers, especially when they’re embedded in a dense, nonfriable matrix. In materials like floor tile or plaster, asbestos fibers can be extremely narrow and tightly bound within the cementitious matrix, which makes them hard to see with PLM. Because PLM relies on visual detection of fibers in a prepared mount, those ultra-thin fibers may escape notice, requiring more sensitive techniques (like TEM) to confirm presence. Drywall, glass, and wood don’t pose this same combination of being nonfriable and containing such ultra-thin fibers in a way that makes PLM particularly prone to miss them, so the scenario points to nonfriable materials such as floor tile or plaster as the ones PLM might miss.