Van Orden, D.R., J.M. Wilmoth and M. Sanchez, “Effect of Size Reduction Processes on the Apparent Fiber Content of Rock Samples”, The Microscope, Vol. 60(1), 2012.
Natural occurrences of asbestos and potential exposure to such materials have drawn significant public and regulatory interest in recent years. Revisions to a published analytical method, CARB 435, that incorporate inappropriate sample comminution strategies have been examined. Tests demonstrating the effects of grinding and preparation of asbestos minerals have been conducted. Sample preparation procedures used by some laboratories in apparent compliance with CARB 435 destroy the characteristics of asbestos, thereby potentially biasing the results. The authors are proposing that the grinding be done in stages, removing the fines at each stage, in order to minimize the effects of grinding. These tests also show that when non-asbestos amphibole particles are crushed, elongated particles are created that could be confused with asbestos fibers (false positives in various analyses). The effects of sample comminution must be considered when creating or revising asbestos analytical procedures.