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IDENTIFICATION OF ASBESTOS
To examine whether asbestos is present in a material sample, light microscopy is used. The appearance and the light refraction are used to distinguish between asbestos and other fibers, and to identify the type of asbestos in the sample. Asbestos in dust and air samples is analysed with scanning electron microscopy (SEM).
MATERIAL SAMPLES
During demolition work, it is often important to ascertain whether asbestos is present in the construction materials or not. Asbestos may be found in insulation, floor tiles, adhesives etc. Material samples that are sent to the laboratory are first examined using a stereo microscope. Sometimes it is possible to detect potential asbestos fibers at this first stage. They can then be hand-picked for examination with a microscope. Most often, however, a subsample is ground for homogenization, diluted with acetone and ultrasonicated. One or two drops of the suspension are then added to an object glass. After drying, refraction oil is added and a cover glass applied. The sample is then ready for examination with a microscope.
Examination under the microscope allows the presence of asbestos to be verified and provides a rough estimate of the amount. By mixing the sample with different refraction oils until the refraction is the same in the fiber as in the oil, it is possible to identify the fiber type. The fiber types include chrysotile, anthophyllite, tremolite, amosite (asbestos gruenerite) and crocidolite.
ASBESTOS FIBERS IN AIR
For detection of airborne asbestos fibers, which often are thinner than fibers from material samples, higher magnification is needed than can be achieved with light microscopy. Asbestos in dust or from air samples is therefore examined using scanning electron microscopy (SEM) with a magnification of up to several thousand times.
Dust samples are analyzed for asbestos when contamination from asbestos removal or from other asbestos sources is suspected.
To be able to distinguish airborne asbestos fibers from other fibers, a special sampling technique is used. Air is being pumped through a polycarbonate filter, which is then examined using SEM. Asbestos fibers are very small (often <0,0005 mm in diameter). In order to quantify the asbestos concentration, the sample has to be studied at 1000–2000 times magnification. The microscope is equipped with an energy dispersive sector, which allows the chemical compostion of the fibers to be determined. Thereby, the different types of asbestos fibers can be separated.
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FIBER COUNTING
The concentration of asbestos fibers in air can be determined by sampling on a filter (filter for total dust or polycarbonate filter). The filter for total dust is analyzed using light microscopy. All fibers with thicknesses between 1and 3 µm are counted, regardless of fiber type. Given the volume of sampled air, the fiber concentration expressed as numbers per ml can be calculated.
SOLVENTS
To measure levels of organic solvents in air, samplers with organic carbon, either carbon tubes or diffusion samplers, are used. The solvents are adsorbed by the carbon, i.e., the solvents attach to the surfaces of the carbon, and are then analyzed by gas chromatography (GC). Since no pumping is required when the diffusion samplers are used, the method is referred to as passive sampling. The small samplers are attached to clothing close to a person's breathing zone. Almost all organic solvents can be sampled, e.g., benzene, styrene, xylene, ethylbenzene and toluene.
Please contact the laboratory for a discussion about sampling and to order diffusion samplers.
TENAX TUBES
Carbon tubes contain active carbon that adsorb various compounds from the air. Tenax tubes instead contain a porous polymer as adsorbant. Depending on the compounds to be measured, either tube is chosen.
The main advantage with using a Tenax tube is that they enable longer sampling periods. The initial extraction of the adsorbant (vätskeeluering), necessary for the analysis of carbon tubes, is not needed when Tenax tubes are used. The Tenax tube is instead inserted directly into the analytical instrument and heated in an inert gas flow to release the adsorbed compounds. This process is referred to as thermic eluation(?). Furthermore, Tenax tubes are recyclable. After the thermal eluation, all compounds have been released and the tube is clean again. |
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