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TEM in Asbestos Identification and Quantitative Analysis by Ronan Tartivel & Michael Shepherd


Caroline Langley
(@caroline-langley)
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Joined: 2 years ago
Posts: 5
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The webinar will shortly be available on the FAMANZ website (members side). It generated a lot of discussion amongst participants. A few of the questions & comments by participants (edited) are below. Please feel free to continue the discussion:

Frank Ehrenfeld: 120 hour training course condensed into 25 minutes. Good general information. I have many questions and comments too many for chat function.

Derek Miller: How important do you think we move towards use of TEM in Aus & NZ, and should it become the prominent method? Response from Shelley Rowlett: Not until we have a standard we agree to use for the results.

Frank Ehrenfeld: Can you speak to prep challenges for TEM filters such as filter collapsing, plasma etcher calibrations and impact of too aggressive etching, loss of fibers during prep and (yes, possible) the 'creation' of fibers during prep.

Philip Hibbs: In relation to the use of TEM for airborne fibre samples, how do you compare the TEM results to the relevant airborne fibre guidelines which are based on PCM and therefore a different resolution to TEM?

de021 (identity unknown): For zero tolerance regulations sample representation remains a significant issue. Such a small amount taken from a large bulk. What are the systems in place other than possibly doing a 1000 takes?

Frank Ehrenfeld: For edification - the six regulated asbestos mineral EDS patterns are the same elemental spectra for dozens of silicates and/or polymorphs, TEM thus requires SAED and morphology to be declarative. Costs of TEM laboratory - assuming all new prep equipment and instruments (NOT counting staffing)...

Laurie Glossop: SEM provides good 3D images whereas TEM is only 2D images and does not allow to show shape. SEM is also better for seeing whether a fibre is asbestos/asbestos bundle or cleavage fragments. You really need to be a mineralogist to assess the EDS from SEM problem that epidemiology is based on PCM.

Laurie Glossop: In mining it is important to determine if the fibres are asbestos or cleavage fragments

Frank Ehrenfeld: HEPA hoods, furnace, filtration, pumps, vibration free and controlled electrical field environment, LTA, high vacuum carbon evaporator, double tilt and cryo specimen holders, LN2, EDS, digital camera, reference materials, etc. It can become quite expensive. Yet, many decent quality used TEMs are on market.

Frank Ehrenfeld: Many studies showing SEM reports false positives and false negatives. Laurie Glossop responded to Frank by PM.

Linda Apthorpe: good point Michael re analyst experience and expertise, and also re a combination of methods and data/information collected to unequivocally ID the fibres, and even then, it is very difficult for some fibre types, particularly NOA!

Laurie Glossop: The definition of tremolite or actinolite is not well defined and arbitrary.....percentage of Fe defines to some degree......if more that 3% Fe actinolite

Carl Strautins: IMA define as 0.9 ratio of Mg/(Mg+Fe) ratio for differentiation between actinolite and tremolite

Laurie Glossop: Counting and speciation on SEM you need to allow about 30 minutes for a typical sample by a skilled analyst

Linda Apthorpe: Consider these points re prep and analysis time re cost - TEM is awesome, but not for everyday samples!

Frank Ehrenfeld: Over last 40 years of TEM analytical method development across the globe is starting to be focused more on 'counting' everything and then recording mineral structure dimensions, chemistry, crystal structure and the indexing the results by the end-user for different purposes (ex. exposure assessment, risk assessment, etc.)


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Caroline Langley
(@caroline-langley)
Member Admin
Joined: 2 years ago
Posts: 5
Topic starter  

Question from Dr Jimmy Bester:

"The webinar highlighted the numerous weaknesses of the century old PLM-DS analytical technique – which is still the preferred technique in the 16-year-old (unchanged) AS 4964 Standard. Would be interesting to compare the TEM technique (2 hrs sample prep + 2 hrs scanning) against the portable near-infrared spectrometer (PNIRS) that can accurately identify all 6 the Regulated asbestos types, on-site, within 6 seconds, with an accuracy of around 98% - and keeping asbestos and disposal site workers safe?"  

Kind regards Jimmy


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