Samples are collected as prescribed by the CNESST. Sampling of materials likely to contain asbestos (MSCA) is done by “area presenting similar works” (ZPSO). By MSCA we mean a component of the building (eg ceiling), If the component is not uniform (eg If the plaster is different in several places, they will be part of different ZPSOs). In order to have a representative sampling and to be sure beyond any reasonable doubt that an MSCA does not contain asbestos, a total of 9 samples per ZPSO is necessary. As for vermiculite, sampling will be done at 3 different locations to obtain a representative sample.
The IRSST MA244 laboratory analysis technique allows the identification of asbestos fibers or other natural and artificial mineral fibers. It allows a semi-quantitative determination of fiber content in bulk samples, expressed as a percentage (V/V). The analysis is done first by separating the different layers of the sample. Each layer is homogenized to do the analysis well. Layer by layer, there is an inspection under the stereomicroscope to verify the presence of fibers of one of the six types of asbestos (Actinolite, Amosite, Anthophyllite, Chrysotile, Crocidolite and Tremolite). If detection is possible with a stereomicroscope, the analysis continues with a polarized light microscope (MLP) to characterize the type of asbestos. Non-friable materials such as floor tiles should be analyzed by transmission electron microscopy (TEM), since if there is asbestos, the fibers are too fine to be detected by MLP.
Each layer of each sample will be presented according to asbestos concentrations. Concentrations range from no fiber to a concentration greater than 90%. If the sample contains more than 0.1% asbestos, it is considered contaminated according to the safety code for construction work in Quebec.
Daily or final samples are taken according to a rate and time that will allow obtaining a fiber density per square millimeter between 100 and 1300, which is the detection limit according to the IRSST method MA243. There is always a field blank that is included in each analysis, since it serves as a negative control during the analysis. Typically, daily sample collection takes 20 minutes, while a final test takes 4 hours.
The IRSST's MA243 laboratory analysis technique makes it possible to calculate the number of fibers, without distinguishing whether they are asbestos fibers or not, per cubic centimeter. The analysis is done by phase contrast microscopy by counting the fibers on a number of fields. The density is then calculated in order to be able to use this density and calculate the result according to the volume taken. There is always a blank which serves as a negative control by subtracting the density of the blank from the field samples.
For preventive measures, if a sample taken during the asbestos removal work does not comply with the requirements and has a concentration higher than 0.01 fibres/cm3, it will be necessary to increase the suction at the source and/or to increase the humidification of the materials in order to reduce the emission of dust during the works.
If a sample taken following the asbestos removal work does not comply with the requirements and has a concentration higher than 0.01 fibres/cm3, it will be necessary to continue air filtration with a HEPA-certified filter combined with suction. of all surfaces in the work area.
It is sometimes recommended, when a test is not compliant, to continue with a TEM transmission electron microscopy analysis according to the NIOSH 7402 technique in order to check whether the presence of fibers in the air corresponds to asbestos or not. .
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