However if a laboratory is accredited for ACM or fibre quantification they can assign a limit of detection or quantification to the previous procedures if no material or fibres were detected.
ASBESTOS IDENTIFICATION IN BULK SAMPLES The suspected bulk ACM is examined under a stereo- microscope, in a dust control cabinet, by a qualified Asbestos Analyst. Any fibres found are removed and mounted for Polarised Light Microscopy (PLM) according to the guidance in HSG248 Asbestos: The analysts guide for sampling, analysis and clearance procedures, HSE, 2005.
Asbestos is reported as Not Detected, Trace (if only one or two fibres are found) or Detected and the asbestos type/s present are reported in a format complying with the HSE guidance.
SEMI- QUANTITATIVE % OF ACM IN SOIL This method allows for the percentage on a dry weight basis of the amount of asbestos in ACM recovered from a soil sample to be reported after identification for assessment against regulations for the disposal of hazardous/special wastes.
The method has a limit of detection of <0.1% for sample weights of typically between 200g and 1kg, and samples will be reported as either <0.1% (ie not detected) or >0.1%. It is now however becoming a requirement that if no ACM is found a fibre screen must be undertaken to ensure that the trigger level of 0.1% is not exceeded by gross fibre contamination.
FIBRE QUANTIFICATION If quantification of asbestos fibres in the soil is required this is currently only available at a few laboratories. This method is often referenced as HSE REPORT No. 83/1996 Method 5. If a screened sample contains fibres a sub-sample is suspended in water and aliquots are removed and filtered. the filter is examined under phase contrast microscope and the fibres are counted and sized. The mass is estimated based upon the density of the material.
The limit of quantification is typically 0.001% with reported limit of detections of 0.0001%
With an appreciation of the services available pricing work and scheduling testing should be quite straightforward. However the possibility of tiered options with dependent options do not necessarily assist in this.
Expectations vary enormously, many projects are priced on rates and there is no regulated guidance on soil guideline values that would define the tests in a way that could be universally accepted. As an industry it must be acknowledged that the level of skill and time required in looking for lumps of ACM, compared to quantifying fibres to <0.001%, is significant and this impacts upon cost and turnaround.
Going forward consistent specifications of the testing requirements will enable laboratories to plan and develop the services required. However that will not tackle the old nut of what is the risk and how do you sample for it?
A number of groups are currently working to assign soil guidance values and good working practice for soils containing asbestos. However it should be recognised that there is already a range of expectations and published information. Therefore any further recommendations should add clarity so as to ensure that all involved will have risk derived limits and robust accredited data with which to make decisions.
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