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The Asbestos Air Monitoring Myth
Air testing is a regular part of the work carried out by UKAS accredited analytical companies. It is often employed to permit re-occupation of an area after licensed asbestos removal, or to provide reassurance that an area does not have dangerous airborne levels. In principal this sounds like a really useful tool for asbestos management. Most clients want comfort that their staff are safe and will not be exposed to harmful levels of asbestos.
There is one major problem though; the majority of air testing is a meaningless waste of money which does not actually answer the question that clients want answered:
"Is it safe?"
Well there lies a problem, what is safe? Although I have tried to keep this simple, I apologise if this gets overly technical.
Epidemiological studies such as Hodgson and Darnton (2000) suggest that 0.01 f/ml is not a safe level , it is estimated that up to 100 deaths per 100,000 may occur if exposed to crocidolite at 0.01f/ml yrs. This is 1,000 times over the HSE acceptable level of risk as set out in their policy document (R2P2).
The Supreme Court ruled in 2011 that any exposure over ambient levels carries a risk of harm. According to the MRC (1997), ambient levels of asbestos are typically 0.0001-0.000001 f/ml, and also state that buildings which contain asbestos in good condition, have typical asbestos fibre levels of 0.0005 f/ml.
Monitoring to prevent exposure to asbestos must be carried out according to EU Directive 2009/148/EC. The Directive states: "Taking account of the latest technical expertise, it is necessary to specify the sampling methodology to be used to measure the asbestos level in air and the method of counting fibres". The EU Directive on carcinogens 2004/37/EC, requires that employers reduce exposure to the lowest level technically possible. This is ignored by the HSE who use the term "lowest level reasonably practicable".
By law, analytical companies carrying out air monitoring for asbestos must be accredited to meet the requirements of ISO 17025 (UKAS accreditation). Analysts are bound by this to follow HSE guidance "The Analysts Guide" (HSG248) which sets out the methods to be used for sampling and analysis, this is based in part on the WHO 1997 guidelines, but omits some of the flexibility in the method which would allow analysts to achieve greater analytical sensitivity.
The problem is that analysts are normally limited in the sensitivity of their monitoring to the methods permitted under their UKAS accreditation, which is bound to HSE guidance HSG248. As such, analysts nearly always only monitor to a limit of detection of 0.01 fibres per ml of air. Often results reported to clients are deemed "satisfactory" if the concentration is somewhere below this level. So the client is happy that the environment is "safe".
Another weakness of the current method is that there is huge variation in the repeatability of results. A typical result of 0.01 f/ml (roughly 20 fibres) could actually when repeated, be a count of 37 fibres or as low as 10. A concentration could potentially be almost double that reported, if the count was repeated. If the threshold was limited to 10 fibres counted, then the highest 95% confidence limit would be 21 fibres counted, which is much more agreeable. Fundamentally this method represents bad science and is grossly misleading.
Achieving a resolution of 0.0005 f/ml and below is easily possible with the right methods. This can enable clients to demonstrate that their asbestos is in good condition in line with the MRC statement.
A variety of methods exist to provide greater sensitivity, electron microscopy can be used, or by using conventional microscopes, larger samples of air can be taken and a greater number of fields examined. Size selecting sampling heads, such as the impactor recently designed by Robin Howie will prevent problems of filter occlusion caused by non asbestos dust particles.
The reason why analysts are producing meaningless results, is because the rigid methods connected to their accreditation and limitations of HSE guidance prevent the application of good science. Analysts are also not taught to sample in any other way than that set out in HSG 248, and often refuse to sample to higher resolutions because they do not understand typical background fibre levels. I started in the asbestos industry in 2006. On my first day I was shown how to run a sampling pump and use a microscope. On my second day I was audited by an external UKAS assessor who passed me with flying colours. Looking back I understand fully why the standard of air testing is so poor.
In the UK we are falling short of our requirements to adequately measure and prevent exposure to asbestos in our workplaces and schools, and are falling behind many EU countries in this area. Until either clients request meaningful representative monitoring, or the HSE adjusts its guidance, we will be blindly exposing people to unknown risks, a lesson from the past - still not yet learnt.
If client's don't demand better analysis, it will never be provided.
by Marcus Hill