PLM by EPA 600/M4-82-020
In 1979, under contract to EPA and to support the "Asbestos-in-Schools" program, Research Triangle Institute(RTI) assembled a group of analysts to discuss and develop protocols for analyzing asbestos in bulk insulation. These discussions led to the development of a formal protocol using polarized light microscopy (PLM) and x-ray powder diffraction (XRD) analytical techniques. The protocol was drafted and evaluated by RTI in a multi-laboratory round-robin study using control samples. This effort resulted in the publication Interim Method for the Determination of Asbestos in Bulk Insulation Samples, EPA -600/M4-82-020 (1982).
In this method, the laboratories are called to use Polarized Light Microscopy as the means of testing, and it outlines the clear procedures for sample preparation, sample analysis, results determination and quantization.
The method recommends using forceps at different locations of a sample to make sub samples. Samples are then immersed in refractive index liquid on microscope slides, teased apart, homogenized and covered with cover slips. At times, interference to the sample should be eliminated. For size reduction of the sample, a mortar and pestle are recommended. Contamination issue is dressed and special techniques for prepare amphiboles and vermiculite.
The first step is to determine whether fibers are isotropic or anisotropic. If the fiber is anisotropic, which asbestos are, determine its extinction patterns. If the extinction is negative, mount the fiber in 1.700 RI to determine whether it is Crocidolite. Otherwise follow steps to identify fibers among the other types of asbestos.
If fibers are not present, the method calls to prepare two more slides to confirm the absence of fibers, hence asbestos.