Follow the procedure in the Environmental Protection Agency (EPA) Silver Book, or “Measuring Airborne Asbestos Following an Abatement Action (EPA-600/4-85-049)” specifically outlined in Chapter 4, page 5. The volume required to reliably quantify fibers down to 0.01 f/cm3 may be calculated using the first formula on this page. Note that for the National Institute for Occupational Safety and Health (NIOSH) 7400, the minimum fiber loading is specified. Also, alert labs that the area of viewing for a field will vary between microscopes and that they must determine this value from their microscopes. You can obtain a copy of the EPA Silver Book by calling the TSCA Hotline at 202-554-1404.