The 198.4 method is New York State's Transmission Electron Microscopy (TEM) method for the analysis of asbestos in Non-friable Organically Bound building materials. It typically follows a 198.1 (PLM) analysis as both are required in order to classify a material as a Non Asbestos Containing Material (non ACM).
Samples such as floor tiles and roofing materials are not condusive to asbestos analysis. This is because the asbestos (if present) is usually tightly bound to the matrix material and therefore not easily isolated and detected by microscopy.
These types of materials are classified as Non-friable Organically Bound (NOB). Some examples of NOB materials include:
- Floor tiles (vinyl and asphalt)
- Roofing Materials
PLM cannot detect asbestos fibers less than 0.2 microns in diameter. Because asbestos fibers found in NOB materials are often less than 0.1 microns in diameter this method can sometimes yield low estimates or even false negative results. Conversely, TEM analysis, performed at a much higher magnification can sometimes miss extremely large amphibole asbestos fibers. It is for this reason that both PLM NOB and TEM NOB analyses must be performed before a material can be classified as Non Asbestos Containing Material (non ACM)
Sample retention time - 60 days