by Tom


by Tom


We are often asked what is safe.  The official answer is that a fibre concentration of 0.01 fibres per ml of air is considered safe.  This comes from HSE guidance, first introduced to guidance in the 1980’s (EH10) and it has been carried on ever since.  The guidance specified that where 0.01 f/ml was exceeded following asbestos removal works that remedial action should be taken before reoccupation.  Below this level then the environment was considered safe.  This is now known as the “clearance indicator”.

The Clearance Indicator is still used today following asbestos removal work, and is normally part of a more in-depth clearance known as a four-stage clearance.  It is also used more generally, and often misused and misunderstood.

Employers and Duty Holders often see it as an absolute indicator of safety or that there are no asbestos fibres present.

While 0.01 fibres/ml sounds very low.  But if we scale this up to cubic meters it equates to 10,000 fibres.  All of a sudden it doesn’t sound so safe, especially while asbestos training companies are still telling people that one fibre can kill.

Despite 0.01 f/ml being the allowed limit, it does not necessarily constitute a safe level.  If you are now wondering what the safe level is then you will be disappointed to find there isn’t one.

What is considered a safe level is for the competent asbestos analyst or consultant to decide.  Air testing is not limited to “the test” but also about proper advice for a given situation.  If an analyst passes an air test based on fibre concentration but sees suspicious-looking fibres down the microscope then they should investigate further – the test result is not the end.

Asbestos is present in the natural environment – to get a full picture then ideally a background test needs to be carried out and compared to the work area / enclosure.  This isn’t commercially viable so will rarely be carried out.

Failing air tests and four-stage clearances is also not commercially viable, since the analysts are more often employed by the company they are testing, and no asbestos removal company is going to keep booking an analyst that is too thorough.  For this reason we always recommend resisting the simplicity of letting the asbestos removal contractor “deal with it all for you” and employing your own analyst who is working with you and with your interests in mind.

HSE guidance cannot provide all the answers about what is a safe level, but the competent person/analyst/consultant should be able to and should be able to adapt the tests to the situation.

One last, but important, fact about air testing is that air testing is not limited to asbestos.  All respirable fibres within a certain size range are counted in each sample of air.  This can include carbon, dust, fibreglass and much more.  Anything that is >5 µm long, <3 µm wide and a length to width (aspect ratio) of >3:1 will be counted, and the UKAS accredited analyst cannot report on fibre types even though if they are experienced enough they will recognise and be able to identify the fibres.  It is an air quality test, that coincidentally is used as a benchmark for asbestos removal projects.

While on the subject of safe levels we can discuss the scaremongering which is becoming a regular theme in our industry.  This is also sometimes called “dust swabbing” and is when a surveyor takes a dust sample and sends it to a lab who will quite often find asbestos fibres in it.

The reason asbestos fibres are quite often found is that, as above, asbestos is in the air naturally and can settle anywhere.  Buildings that contain asbestos are more common, and if you take an asbestos removal project as an example and think about the safe levels you could find in a standard lounge of 4m x 4m x 2m (32 SQM) you could well find 32,000 fibres that are “safely just there”.  This can lead to misguided advice in the form of recommending environmental cleans etc.

I will write another post about “dust swabbing”, but generally it can be useful sometimes but on the whole it is not used properly and with so many companies interlinked these days there can be some serious conflicts of interest.  We are in the minority of not being owned by or linked to any asbestos removal companies so we like to think our advice can be trusted.  When we require the assistance of an analyst for our surveys we do not stick with one company – we purposely distance ourselves and use different companies irregularly as we want results and facts not favours.

So to summarise, a pass on an air test may not always be an indicator of safety but also the fibres counted may not always be asbestos so in that respect a fail may also not always be unsafe with regards to asbestos.

Hire your own analyst!


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