Polarized light microscopy (PLM) analysis is the most commonly accepted technique for analysing bulk samples for asbestos. Bulk material samples are typically collected during an asbestos survey as required by the Ontario Regulation 278/05. The PLM analysis is based on optical mineralogy and uses a phase contrast microscope equipped with polarizing filters. Identification of asbestos is based on the determination of optical properties displayed when the sample is treated with various dispersion staining liquids. Identification is further substantiated by fibre morphology and the effect of polarized light on the fibres. PLM analysis is specific to fibrous materials and allows for the determination of:

Presence and amount of asbestos in the sample, and

Type of asbestos (Chrysotile, Amosite, Crocidolite, other).

The limit of detection of the PLM is below 1% but not higher than 0.1% asbestos. Analytical method EPA 600, which is specified by Ontario Regulation 278 has detection limit of 0.5% asbestos.

Samples of non-friable organically bound (NOB) materials like vinyl asbestos floor tiles, mastics or roofing tars require additional pre-treatment with a solvent or preparation in a furnace.
The PLM requires approximately one gram of sample material, is fast and inexpensive. The disadvantages of PLM analysis include:

Asbestos is not detectable at low concentrations,

Very fine asbestos fibres, such as those in brake dusts may
not be detectable,

Analysis may not be representative for small heterogeneous

Accuracy of analysis is dependant on experience of analyst.

The PLM analysis is adequate for most asbestos analytical needs. Where necessary, alternative laboratory services are available. These include transmission electron microscopy (TEM) and scanning electron microscopy (SEM).

The procedures for sample analysis are fully described by the US Occupational Safety and Health Administration (OSHA) as analytical method ID-181 and by the US Environmental Protection Agency (EPA) as analytical method 600/R93-116, including NIOSH method 9002. EPA method 600 is referenced in Ontario Regulation 278 as analytical choice for analysis of samples of building materials for asbestos.

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Polarized Light Microscopy (PLM)

Analysis of Bulk Samples for Asbestos (EPA method 600)