Laboratory Method for the Assessment of Respirable Asbestos Fibre Release
Traditional laboratory asbestos methods (including those recommended in the as yet unpublished SCA Blue Book method for Asbestos Quantification) provide a significant amount of data as to what is present within a soil, but are of limited use in determining how it will behave and therefore what risk it represents.
These existing methods can give a qualitative description of the asbestos present, both in terms of fibre type but also the nature of the fibres present (free fibres, fibre bundles, Asbestos containing material), along with a percentage content (by mass). In recent years, this has been taken slightly further with labs providing more detailed breakdowns of individual fibre/ACM types, and with the availability of Phase Contrast Optical Microscopy (PCOM) we can also provide details of individual fibres found, specifically focussing on those which would be respirable (of a specific length/width to pass into the terminal bronchioles of the lungs, potentially causing Asbestosis and Mesothelioma).
As good as this is, it is a “worst case” scenario, as all we know is that these high risk fibres are there and ‘could’ be an issue. What is needed is a way to determine under realistic conditions whether they actually ‘will’. One option is to monitor conditions on site, either using personal air sampling equipment equipped with filters intended to capture the asbestos, or by creating an enclosed space and agitating the ground and extracting the air again through a filter. Both approaches are followed by traditional fibre counting techniques on the filter. Either will give a good indication of the ‘fibre release’ but are very visible techniques on site and require the deployment of specific equipment and additional personnel.
The direction we have taken is to look at a laboratory method for producing this kind of ‘real’ site specific data using a standard soil submission for Asbestos screening. Taking an existing British Standard for dust generation (BS15051) we have modified the process to focus on testing soil samples for the generation of respirable asbestos fibres.
Using a rotating drum under constant air flow, dust (including the respirable fibres) is generated and captured using a series of foam and membrane filters, the latter then subject to fibre counting by PCOM to determine the number of respirable fibres released and the fibre concentration in air (fibres/cm3). The total mass of dust released is calculated gravimetrically and a dust concentration produced (mg/m3).
Having both the fibre and dust concentration allows for normalisation of the fibre/cm3 result based on particular dust levels, either from regulation/guidance or based on real dust monitoring carried out on site.
The process is infinitely variable, allowing the lab to tailor the analysis to provide data that is relevant to the questions being asked. Running the soil post-drying gives a conservative approach, as a dried soil is known to release fibre more easily. Running as received may give more detail on the soil as it would be in-situ, or artificially altering the moisture content could lead to conclusions over optimum conditions for inhibition of release. Recent investigations have also begun using this methodology for the potential for differing stabilisation agents to reduce fibre release from sites with known asbestos issues.
• Laboratory based determination of fibre release
• UKAS Accredited methodology
• Bespoke analytical solutions
• Filling the gap in risk assessment
Dr Claire Stone and Will Fardon
COMPANY NAME: i2 Analytical Ltd
PHONE: 01923 225 404