Field Technique for Clearing Cellulose Ester Filters Used in Asbestos Sampling

Abstract

Abstract A field procedure to clear cellulose ester filters used for fiber counting, without the need for boiling or heating acetone as prescribed in the National Institute for Occupational Safety and Health's Method #7400, is presented. The method is simple and requires only that the analyst place the filter wedges/halves on the microscope slide, weight the edges of the filter to prevent curling, place the preparation in a covered dish containing acetone, and allow the filter to clear at room temperature. Filters from previous Proficiency and Analytical Testing (PAT) samples were cleared utilizing the cold acetone clearing technique. Results obtained with the new technique were in good agreement with the reference values and well within the performance limits of the round. Filter clearing time varies, with a suitable result usually obtainable in approximately fifteen minutes. We believe this clearing technique can be substituted for the hot acetone clearing method, when necessary, without degrading analy...