PLM Bulk Testing
Asbestos PLM bulk sampling is usually done on mud, tape, duct wrap, etc., to prove asbestos is not present. This reduces or eliminates removal and disposal fees.
The AHERA regulation requires that all bulk samples be analyzed by Polarized Light Microscopy (PLM). This method uses a light microscope that is equipped with polarizing filters. Asbestos is identified by various visual properties that show up when the sample is treated with dispersion staining fluids. Further identification of asbestos in the sample is based on structural characteristics. Additional information can be obtained about the asbestos content of the sample by the use of X-ray diffraction (XRD). This additional method is usually only used if the percentae of suspected asbestos is 3% or more but the microscopist has some trouble positively identifying the fibers as asbestos.
PLM is relatively inexpensive. AHERA requires and EPA suggests for all non-school buildings that laboratories performing Polarized Light Microscopy of bulk samples participate in an accreditation program provided by the National Institute of Standards and Technology (NIST) called the national Voluntary Lab Accredition program (NVLAP). This program is to ensure standardization of laboratory qualifications and performance when analyzing bulk samples.
The AHERA regulation states that in order to prove that a homogeneous area of suspect ACBM is not an asbestos-containing material, the results of ALL SAMPLES REQUIRED TO BE COLLECTED indicated asbestos in amounts equal to or less than 1% asbestos. For example, a homogeneous area of surfacing material covering 6000 square feet was sampled according the AHERA protocol. Seven samples were collected in a random manner. EACH of these samples must be analyzed and obtain a reasult of <1% for the area to be declared a non-ACM material.
A homogeneous areas of suspect ACBM is considered to be an asbestos-containing material if at least ONE of the required number of samples is greater than 1%.
NESHAP regulations require that if an analytical result is less than 10%, the owner or operator of a demolition/renovation project must reanalyze the sample by a method of PLM called point counting. Alternatively, the owner or operator can merely assume the material is asbestos-containing without conducting point counting. indirectly, the EPA is saying that normal PLM microscopy is suspect in terms of accuracy at levels below 10%. However, the limit of detection for PLM is considered to be 1% by area.
