A modification of the NIOSH Analytical Method P-and-CAM-239 for asbestos (1332214) fibers in air was presented. In the usual method, cellulose-acetate filters used for the collection of asbestos fibers were cleared by the hot acetone/triacetin method. The authors point out that this procedure requires several pieces of equipment including a hotplate and that there is a safety hazard associated with the heating of a liquid such as acetone. In the modified procedure, a filter was placed on a microscope slide, the edges weighted with a bacterial counting cell (Dunn Cell) to prevent curling, and the slide placed in a covered petri dish over a small amount of acetone. The acetone would clear the filter within 10 to 15 minutes, after which any curled edges could be trimmed and the cleared filter fixed with triacetin. In order to test if identical fiber counts were obtained with the modified and original procedures, a series of NIOSH Proficiency and Analytical Testing filters were counted after they had been cleared by the hot acetone vapor, cool acetone vapor, and standard clearing solution. A reasonably good agreement was found between the three methods. The authors conclude that the modified procedure reduces the safety hazard of using hot acetone, and they recommend it for use in the field.