Developments in the RICE asbestos fibre counting scheme, 1992-2000. Regular Interlaboratory Counting Exchanges

Area of Science:

• Occupational Health
• Environmental Science
• Analytical Chemistry

Background:

• The UK's Regular Interlaboratory Counting Exchanges (RICE) scheme is crucial for proficiency testing in asbestos fibre counting.
• Historically, RICE used industrial samples and automated image analysis for reference values.
• Changes in sample types and reference value determination were implemented in 1992.

Purpose of the Study:

• To evaluate the reliability of new reference values introduced in 1992 compared to older methods.
• To analyze trends in asbestos fibre counting levels based on sample density.
• To assess the impact of sample density range on laboratory counting accuracy.

Main Methods:

• Analysis of extensive data from 28 rounds of RICE sample exchanges.
• Comparison of reference values derived from automated image analysis versus laboratory medians.
• Examination of asbestos fibre counting trends across different sample densities (low and high).

Main Results:

• New reference values (medians of laboratory determinations) are more reliable than old ones (automated counts).
• Asbestos fibre counting levels stabilized in low-density samples after initial increases.
• High-density samples showed a consistent decrease in counting levels of approximately 0.5% per round.

Conclusions:

• The shift to median-based reference values and wider sample density range enhances the reliability of asbestos fibre quantification.
• Observed counting trends suggest reduced bias and better reflection of routine laboratory practices.
• Findings have implications for evolving asbestos counting rules and occupational exposure assessments.