Asbestos – An overview with Philip Hibbs

Principal Consultant, Hibbs & Associates Pty Ltd

The health issues associated with exposure to asbestos fibres have been well publicised. However, many people do not realise that asbestos is a naturally occuring fibrous mineral. The asbestos minerals have a distinctive and almost unique combination of physical and chemical properties, which at one time gave them great commercial value and an almost indispensable place in industry. Its use spanned most of the last century, and millions of tonnes of asbestos have been mined and many thousands of everyday products have been produced that incorporate asbestos.
It is unfortunate that the very properties of the asbestos minerals that make them industrially useful, also contribute to their potential to cause diseases. The health effects is a result from the inhalation of fibres in the “respirable size” range. These fibres are too small to be seen by the unaided eye, but have the optimum aerodynamic characteristics for penetration deep into the small airways of the lungs where they cause damages.
Current scientific knowledge, from epidemiological studies, indicates that the asbestos related diseases exhibit a dose response relationship and a no effect threshold. These studies also indicate very clearly that the development of the asbestos related disease requires significant exposure to asbestos.
Although all forms of asbestos are hazardous and have been shown to cause asbestosis, lung cancer and mesothelioma (the situation is less clear for chrysotile and mesothelioma), there is accumulating evidence that the degree of hazard is intrinsically related to fibre type and fibre size distribution.

How are materials analysed to confirm asbestos content?

In Australia, the standard method to analyse materials for asbestos content is by optical microscopy as described in Australian Standard “AS 4964-2004 Method for the qualitative identification of asbestos in bulk samples”. This method is quick, cost effective, suffers from few interferences and is sensitive.
The samples are examined by stereo microscope and fibrous materials identified are extracted for analysis by polarised light microscopy supplemented with dispersion staining. This method examines the morphology and optical properties of the fibres, for those properties that are unique to the asbestos minerals. The optical properties examined include:

  • Colour and Pleochroism
  • Birefringence
  • Angle of Extinction
  • Sign of Elongation
  • Refractive Index by Dispersion Staining

The ZEISS petrological microscopes are particularly suited to this type of analysis, particularly the ease with which crossed polars and dark field illumination can be achieved.

How are airborne asbestos fibres measured?

The levels of airborne respirable asbestos fibres are assessed in accordance with the requirements of the Safe Work Australia Guidance Note on the Membrane Filter Method for Estimating Airborne Asbestos Fibres, 2nd Edition [NOHSC:3003(2005)]. The analysis of the slide samples requires counting of graticule fields on the membrane filter sample and can be quite tedious. The ease of operation and clarity of the field of view with ZEISS phase contrast microscopes greatly assists with the analytical process.

How long have you used ZEISS microscopes for your analysis?

I have worked as an Occupational Hygienist in the construction industry conducting asbestos assessments and testing for 30+ years. I trained on ZEISS microscopes and have used them ever since.

Why did you choose ZEISS?

I trained on ZEISS stereo and compound microscopes and they seemed the obvious choice. However, I have used other brands of microscopes, but in my opinion the design, functionality, and quality of the ZEISS instruments is superior. The mechanical components and optics of ZEISS mircroscopes are very typical of German high precission equipment, superbly designed and beautifully engineered.
We have a range of ZEISS upright polarised and Stereo microscopes. These have served us well over the last 25 – 30 years and are regularly transported between field laboratories. They are regularly serviced and maintained by ZEISS and are functioning just as well now as when they were new. A testimony to the quality of the engineering. We have recently purchased an additional 2 Stereo microscopes based on the quality, service and partnership we have received from ZEISS. This in turn will continue to allow us to provide our customers with quality analysis and longevity for our business.

Interviewer: Ms Susan Hart
Product Specialist
ZEISS Microscopy Australia