PLM EPA/600/R-93/116 (400 Point Count)

This is a comprehensive method outlining various techniques for determining the asbestos concentration in bulk building materials. While predominantly a Polarized Light Microscopy (PLM) method, other techniques such as X-Ray Diffraction (XRD) and Transmission electron microscopy (TEM) are discussed as well.

The PLM method outlines two quantification techniques.  The first, and most widely employed is the visual estimate.  This works well for most sample types.  The second type of quantification technique is the point count.  While more labor intensive it is somewhat less subjective than a visual estimate.  This can be important especially at low asbestos concentrations.  Both the accuracy and precision are improved with point counting.  And the more points analyzed the better the accuracy and precision of the method.

The 400 point count is used mostly to comply with NESHAP regulations which require that point counting be performed for better precision and accuracy on samples with low concentrations of asbestos.  

Sample retention time - 60 days

reporting limit to <0.25%