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Asbestos Check conducts air sampling to identify asbestos concentration

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Asbestos Check  offers asbestos air sampling services over a range of commercial and domestic properties.

The method of asbestos air sampling is conducted by the process outlined by the National Occupational Health & Safety Commission. This involves sampling a known quantity of air though a filter, fibres impact on the filter, whereby analysis of the filter can determine the number of fibres identified and compared against the exposure standard.

Air pumps used should be pulsation free and be able to maintain a constant flow when the filter is loaded with particulates such as dust. The flow rate should be set to achieve a total of between 500 - 1000 litres over the sample duration, however, should high fibre levels be anticipated, a lower volume of 100 litres will prevent overloading of the filter.

The sampling head consists of a filter holder which is of a metal or conductive cowl (to reduce potential static electricity) measuring 50mm long. The filter comprises a 25mm diameter gridded membrane filer usually of a cellulose material with a 0.8 micrometer pore size.

The pumps with sampling train attached are then set at the required flow to read within 5 percent of true and maintain the flow within 10 percent. At the completion of the monitoring the pumps with sampling train attached are then checked to ensure that a drop of no more than 10 percent has occurred.

With the end caps in place, the filters are transported to the lab and mounted on a microscope slide. Acetone vapour is then applied to dissolve the cellulose filter which then becomes transparent. Glycerol triacetate is then applied and the slide warmed at about 50 degrees for approximately two minutes, clearing the filter so that analysis can begin.

The filter is analysed by a phase contrast microscope using Koehler illumination with a total magnification of approximately 400x (times). The filters are then viewed using a Walton-Beckett circular eyepiece, known as the graticule to provide templates and assist in the fibre counting process.

Fibres with a specific geometry or counting criteria are recorded and 100 difference areas of the slide are viewed to determine the total number of fibres per 100 fields of graticule view. The concentration is fibres within the air is expressed in Fibres per millilitre of air (fibres/mL).

When assessing asbestos control monitoring levels at the boundary below 0.01 fibres/mL, the removal work may continue with control measures, between 0.01 - 0.02. For concentrations above 0.02 the removal work shall stop until the cause for the high concentration are identified and controlled.

In consideration of exposure monitoring, Safe Work Australia’s Hazardous Substances Information Search lists the time weighted exposure (TWA) standard for all asbestos types to be 0.1 fibres/mL.

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