EPA Gravimetric Point Count

Gravimetric point counting is a technique that enhances quantification of asbestos in bulk building materials.

The sample is first dried and then weighed. It is then subjected to high temperature (between 300 deg C to 500 deg C) in a furnace for a period of approximately 6 hours. During this process organic material is oxidized (burned). After cooling the sample is re-weighed and the weight loss recorded.

Further treatment with dilute hydrochloric acid may be used to remove carbonates and other acid soluble substances in the sample. The remaining material is then washed with plain water, dried and weighed. This weight loss is also recorded. The residue is now examined and PLM point counting is performed to determine the concentration of asbestos fibers in the residue. Because we know the weight of the residue we can calculate the concentration of asbestos in the original sample.

Gravimetric point count improves the ability to detect asbestos fibers in the sample and also improves the quantification. This is so because the residue is very often granular particulates rather than a wide variety of materials with vastly different density and mass thereby making more representative slides and improving point counting statistics.