Which method is used to determine the background level of filters in asbestos analysis?

The method used to determine the background level of filters in asbestos analysis is transmission electron microscopy (TEM). TEM is particularly effective in identifying and quantifying asbestos fibers due to its high resolution and ability to visualize materials at the nanometer scale. This allows for a clear assessment of the background level of fibers on filters, distinguishing between asbestos and non-asbestos materials effectively.

In the context of asbestos analysis, determining the background level is crucial because it helps to ensure that the results are reflective of the asbestos presence rather than contamination by environmental fibers. TEM provides the detail needed to ascertain these levels accurately, making it the preferred method in this scenario.

Other methods, while valuable in different contexts, do not provide the same level of specificity or detail that TEM does for evaluating asbestos fibers and determining background levels.