Interpreting Your Asbestos Results

You’ve heard that asbestos may be present in your cement cladding, or vinyl flooring, or textured ceiling, or virtually any other building material used before the 1990s. You’ve had the material tested and you’ve got the laboratory results back with the dreaded words ‘Asbestos Detected’. Or maybe you have had some air monitoring done and the lab tells you that asbestos is ‘below trace level’ or ‘less than 0.01f/ml’.

Without understanding a little bit about how the testing works, understanding exactly what your results mean can be difficult or misleading. Digging a bit deeper can help you interpret your results, and could save you a lot of money!

Bulk Sampling

This is what we call testing a building material to establish its asbestos content. The testing will tell you whether or not asbestos is present in the bag that was sent to the lab. Here are some things that you need to remember

  • The testing is what is known as a ‘qualitative’. This means that the lab can only tell you whether asbestos is present or not. It does not tell you anything about how much asbestos is present, or how ‘friable’ the material is. Friability and the percentage of asbestos in the material are directly related to how dangerous the product could be if damaged or otherwise disturbed.
  • The laboratory testing process is very sensitive, and the lab will analyse everything in the bag. If the tools used to take the sample have also been used to work on asbestos materials in the past, and have not subsequently been carefully cleaned, or if you have stuffed a whole load dirt, grime and dirty odds and ends in the sample bag along with the material you are getting tested, there is a good chance a few asbestos fibres may have snuck in there. And if they have, the lab will find them! Remember, asbestos is extremely common in urban environments where older buildings are present.

Swab Sampling

Also known as swab testing, this usually involves using tape or a wipe to collect dust or debris from hard surfaces. There are a couple of reasons why this type of testing can be particularly misleading.

  • As with bulk sampling above, this is a qualitative test only, and the analysis process is very sensitive. If there are just one or two loose asbestos fibres collected by the wipe, these will be detected by the laboratory. You might have a large number of swab tests done, with many returning a positive result, but the actual amount of asbestos present could be less than you would find in a thumbnail-sized piece of asbestos cement.
  • If your results are accompanied by a survey report, you may also be given a ‘material assessment’ for each item sampled. This assessment is meant to simplify the results to make them easier to understand and gives each material a high, medium, low or very low-risk rating depending on the material type, condition, surface treatment and asbestos type present. The material assessment algorithm is designed to present the risk posed by bulk materials in an easy to understand way. It is not designed to assess the risk posed by trace quantities of asbestos. The material assessment will almost always classify a positive surface sample as ‘high’ risk, and this can be misleading. It is important to put results like this in context by looking at the bigger picture. Where has the asbestos that has been detected come from, and how much of it there is likely to be?

Air Monitoring

The most common air monitoring method used is the membrane filter method. This involves running an air pump that passes a known volume of air through a filter paper. The filter is then mounted on a glass slide and examined under a microscope. The number of respirable particles is then counted, and an equation used to work out what the concentration of respirable particles was in the room or area when the sampling took place. The membrane filter method is used world-wide as it is simple and cost-effective.

  • Although this is the most common method used, the technique is not specific to asbestos fibre. Any fibre or particle that fits the counting criteria will be included in the count, regardless of whether it is asbestos or not. It is therefore important to be cautious when interpreting results of air monitoring conducted in areas where airborne fibre or particles of other types could be present.

  • The technique has several other limitations, which we won’t go into in detail here. The analysis method has a limit of detection equal to 0.01 fibres/millilitre air. This means that the laboratory could count several fibres on the filter or none at all, and they must still report as ‘less than 0.01f/ml’ as there is no way to tell if there is a difference between these two results. In general, you should only worry if the results show airborne fibre above 0.01 f/ml.

This all sounds complicated...

…And yes, it can be. As with any technical process, it is extremely important to understand the limitations of the techniques used. Asbestos is also a very emotive subject, and it is easy to get carried away, with the many horror stories about asbestos-related diseases.

It is certainly important to take the risk posed by asbestos seriously, however it is well worth talking to a qualified and impartial consultant – to undertake sampling for you or help with interpretation if you already have results – before calling the asbestos removal contractors in. Ask them to talk you through the results and what your options are. A good consultant will care about how the samples were taken, and take a holistic approach to assess risk. For the more technically minded, the following references and additional reading materials provide more detail about how asbestos testing and risk assessment is undertaken. All are freely available online.

Technical References & Further Reading

HSG264: Asbestos, The Survey Guide – This guide for conducting asbestos surveys was created by the Health & Safety Executive (HSE) in the UK. It describes, amongst other things, the commonly used material assessment algorithm mentioned in this article, and is the industry standard.

HSG248: The Analysts Guide for Sampling, Analysis and Clearance Procedures – Another HSE document, this guide has a section detailing the bulk analysis technique. The Australian technique commonly used in New Zealand uses the same principles but is not available for free so has not been included here.

[NOHSC:3003(2005)] Guidance Note on the Membrane Filter Method for Estimating Airborne Asbestos Fibres – This is the standard method used to undertake air monitoring in Australia and New Zealand.

Fibresafe NZ is a fully qualified and accredited asbestos management company based in New Zealand. We pride ourselves on our expertise in asbestos-related matters, as well as our quality of service delivery. We aim to help the nation better their understanding of asbestos and find solutions to sort their asbestos-containing materials until they can be removed in a fair and pragmatic approach.

We’re proud to be accredited by IANZ, to the conformance standard ISO/IEC 17020:2012 for surveying and sampling

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