How does PLM accuracy compare to point counting at low asbestos concentrations?

How does PLM accuracy compare to point counting at low asbestos concentrations?

• A. Normal visual estimation is less accurate at low concentrations; point counting is more accurate.
• B. Visual estimation is more accurate than point counting.
• C. Point counting is less accurate than visual estimation.
• D. PLM accuracy is not affected by concentration.

Answer: (A)

When asbestos fibers are present at very low levels, relying on visual estimation tends to be unreliable because fibers are few and easy to miss or misidentify under polarized light. A counting approach, where fibers are tallied in a defined set of fields or on a grid, uses a systematic method that reduces random error and provides a quantitative result with a known sampling error. This makes point counting more accurate at low concentrations. So the best interpretation is that normal visual estimation is less accurate at low concentrations, while point counting is more accurate.

When asbestos fibers are present at very low levels, relying on visual estimation tends to be unreliable because fibers are few and easy to miss or misidentify under polarized light. A counting approach, where fibers are tallied in a defined set of fields or on a grid, uses a systematic method that reduces random error and provides a quantitative result with a known sampling error. This makes point counting more accurate at low concentrations. So the best interpretation is that normal visual estimation is less accurate at low concentrations, while point counting is more accurate.