Polarized Light Microscopy (PLM) is the most common method used to analyze bulk materials for asbestos. ETL, Inc. follows EPA 600/R-93/116 Test Method: Method for the Determination of Asbestos in Bulk Building Materials as well as EPA-600/M4-82-020 Test Method: Interim Method for the Determination of Asbestos in Bulk Insulation Samples.

Results are reported pertaining to what kind of asbestos is found and the percentage of asbestos, as determined by visual estimation. Samples that are found not to contain asbestos or less than 10%, should be point counted as recommended by the EPA.

  1. Point Counting Method

    This method involves a more accurate counting of fibers located within the viewing area. The analyst reads a minimum of 400 points over eight mounted slides using an eye piece with 25 points. The numerical count of asbestos is then subjected to a mathematical formula which determines the area percentage of asbestos much more accurately. ETL performs EPA and New York methods.

  2. Gravimetric Matrix Reduction Method

    This method involves removing as much organic material (such as cellulose or vinyl) as possible in a 4-6 hour ashing period and subsequently removing bicarbonate material (such as gypsum or calcite) in an acid dissolution process. These processes leave behind inorganic material that of which is largely asbestos. This provides a very high resolution and accuracy because the asbestos can be measured by both how much weight was removed as well as area percentage observed through the microscope. ETL performs EPA and New York methods.

  3. PLM Equipment

    We utilize several Olympus, Nikon, Leitz, and Unitron polarized-light microscopes that are accredited by NVLAP to analyze asbestos. We also have ventilated and HEPA-filtered hoods from the McCrone Research Institute as well as chemical and biological hoods.


Asbestos Phase Contrast Microscopy (PCM) gives the fiber concentration of an air cassette filter, following the NIOSH 7400 Method.

NIOSH 7400 Method

  • This method is used for measuring fibrous dust greater than 3 microns in diameter and greater than 5 microns in length. ETL uses the analysis data provided by the client to give a final result in fibers per cubic centimeter.
  • ETL utilizes Olympus CH2 microscopes to perform phase contrast microscopy. We come well equipped with proper calibration of equipment and preparation of samples.


Send us a message requesting an Asbestos Analysis or Mold Analysis quote and an ETL technician will contact you for additional details.

  • 1 + 26 =