Asbestos Analysis – Is it time to switch to FM?

 

Generally speaking, in the United Kingdom if you want to establish the concentration of asbestos fibres in the air from an air test or monitor someone’s exposure to airborne asbestos fibres, we use a method called Phase Contrast Microscopy (PCM). In essence, it involves pulling air through a filter and then using PCM to count and then calculate how many fibres there are for each millilitre of air over the sampling period. 

 

However, this method has its limitations. Many of the fibres counted using PCM may not be asbestos as the method is counting all “fibres” with size parameters as defined in the test method (The WHO Method – ISBN 92 4154496 1), not necessarily “asbestos fibres” as this method is unable to distinguish fibre types. Added to this, the microscope specified in the test method is normally unable to visualise fibres with widths <0.2 micrometres which some authorities maintain can be the most dangerous. Both limitations can have worrying implications, either resulting in unnecessary resources being spent to reduce airborne fibres which aren’t dangerous, or more worryingly, areas being declared fit to be re-occupied while still containing many thousands of airborne asbestos fibres. (BRETT – at 0.009 f/ml the area would pass but still contains hundreds of thousands of fibres in any event) 

 

Despite this PCM is still the recommended and primary method used. The reasons for this are complicated and to a large degree are based on the fact that this has been the method used for decades and has produced the scientific basis for the correlation between asbestos exposure and asbestos disease producing benchmark figures for legislation and compliance. 

 

To move away from this method would be challenging but is it time to look to a better method? 

 

While SEM (scanning electron microscopy) and TEM (transmission electron microscopy) are becoming more prominent, particularly in establishing either more accurate or lower exposures, they generally require samples to be sent away to a laboratory resulting in a protracted time before results are available, whereas PCM gives results within the hour, which often proves crucial. 

 

 

A method of detection called fluorescence microscopy (FM) has recently been used in the detection of airborne asbestos fibres. Interestingly this involves using a protein derived from a bacterium – E. coli to bind to chrysotile asbestos. Similar techniques are also used to identify amphibole asbestos. Once that has been accomplished it enables much more accurate and sensitive counting of airborne asbestos fibres than PCM. In fact, the US National Institute of Health felt that the FM analytical method was “approaching the sensitivity of SEM” while enabling much more rapid results to be produced. 

 

One of the problems for the HSE and HSL to consider is the level of accuracy of FM. FM can identify fibres at a much greater accuracy than PCM and this may mean that the Control Limit (0.1f/ml) or the Clearance Indicator (0.01f/ml) have to be altered or become either more difficult or easier to achieve depending on the circumstances. However, some would argue that more accuracy can only mean progress, and there are few other methods of analysis that have remained unchanged for so many decades. 

 

One further interesting feature of FM is that this method lends itself to Automated Fibre Counting using image processing software. Although not fully developed yet much work is taking place on software that will be able to use a portable fluorescence microscope, on-site, to establish asbestos fibre levels and much greater accuracy than PCM. It’s this potential which might well be the factor in eventually moving asbestos air-borne fibre counting to FM..