Asbestos testing: up in the air

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Asbestos is well established as the single biggest cause of work-related death in the UK. We now understand the management of asbestos better than ever, but do we always get the fundamentals right?

In July 1984 the Health and Safety Executive (HSE) published an update to guidance note EH10, Asbestos – Control Limits, measurement of airborne dust concentrations and the assessment of control measures, which introduced a limit value of 0.01 fibre/ml. The guidance stated that where this value was exceeded following asbestos removal works, remedial action should be taken before reoccupying the location. If there was less than this amount of asbestos in the air, then the environment was notionally safe. So was born the ‘clearance indicator’.

This value is still used today following asbestos removal works, albeit as part of an in-depth post-work assessment process called the four-stage clearance procedure. It is also used more generally, for example, to show that an asbestos enclosure is not leaking or simply to reassure anyone who may be concerned about their asbestos. Many employers and dutyholders will request a test to check that an area is ‘safe’. If the test result is less than 0.01 fibre/ml, it is considered so.

The value has stayed the same, although there have been modifications to the sampling and analytical technique; this value, now nearly 30 years old, is often misused and misunderstood. Employers and dutyholders often see it as a true indication of safety and/or that no asbestos is present. The value has taken on a magical significance as the holy grail of safety in asbestos, but is it really used correctly?

While 0.01 fibre/ml certainly looks a low figure, if it is scaled to fibres per cubic metre of air, the same value becomes 10,000 fibres/cubic metre. Tell an employer that the level is less than 10,000 and they may sit up and take notice. It is the limit allowed by the measurement technique, but certainly not a safe level.

So what is the safe level? There isn’t one. However, published studies tell us that buildings containing asbestos products in good condition have an airborne concentration up to about 0.0005 fibre/ml (or 500 fibre/cubic metre). Again, not a safe level, and such background levels are probably falling as we remove even the asbestos products in good condition. However, this is a better marker of safety than the 30-year- old clearance indicator of 0.01 fibre/ml.

So why do we still use it? For asbestos removal works it is simply a matter of what is practical. The standard method may take an hour to do, but measuring the background levels could take you all day to achieve this level of sensitivity. In some ways it does not matter, as a good asbestos removal project should ensure that once the enclosure is removed, the level in that area falls to background very quickly. It does so because the contractor (verified by the independent analyst) should have made sure all traces of asbestos have been removed as far as reasonably practicable. If there is no asbestos in the room, then anything left in the air (at <0.01 fibre/ml) will quickly dissipate.

For leak testing of asbestos enclosures and for general reassurance we can do better with well thought out sampling strategies. The analyst needs to think about the reason for the test and how best to interpret the findings. If an employer is worried about a location they should not simply put the pump on for an hour, but all day or night, and do not refer to the <0.01 fibre/ml limit, but maybe <0.001 fibre/ml or even <0.0005 fibre/ml. The dutyholder may not understand the numbers but the competent analyst should and should be looking to prove ‘safety’ as far as possible.

Photograph: BOHS

Such matters are for the competent asbestos analyst, consultant or occupational hygienist. Furthermore, air testing is not just about the test but about proper advice for the given situation. If an analyst passes an air test at <0.01 fibre/ml outside an asbestos enclosure but sees suspicious-looking fibres down the microscope, then the analyst should investigate; it is not simply about the test result.

If an employer is worried about a dusty environment, they should not do a disturbed air test to see if it is okay. First, they should seek to understand the environment and whether the dust could contain asbestos. If not, there’s no need for a test, but if it could contain asbestos and is likely to be contaminated, then a disturbed air test would be foolhardy. A non-disturbed air test would be pointless: the dust still needs to be cleaned up.

There are 1,001 situations the competent person may come across that cannot simply be resolved by taking a sample or switching a pump on. HSE guidance cannot answer all the questions, but the competent person should be able to and should be able to adapt the tests to the situation.

Why do surveyors or analysts take dust samples from surfaces and upon finding a single asbestos fibre condemn the environment as ‘contaminated’, only to find, following an ‘environmental clean’, that the room achieves an air test of <0.01 fibre/ml (remember that’s <10,000 fibres in every cubic metre of air)? A further dust sample may find a further fibre, so the air test is meaningless in such a case.

Competency does not come from simply being able to switch on a pump and analyse an air test, but it comes from being able to know how to investigate and resolve any given situation. It comes with experience, from encountering many different situations and learning from peers. It also comes from qualifications that set the trainee on the road to competency.

With such qualifications, candidates can, with experience, progress to a certificate of competency in asbestos. There are many situations that the competent person will come across and be required to advise on, whether it is telling an employer not to worry at all about asbestos-containing sink pads or how to investigate and understand a contaminated environment. Where competency is not achieved, the advice can be poor, dangerous and costly.

Some employers are told to annually inspect their asbestos-containing sink pads or roofing felts even though no meaningful risk exists. They do so along with their high-risk asbestos products. Why not ignore the sink pads and better inspect/manage the really important stuff? The consequence of poor advice can be poorly focused and costly asbestos management strategies.

A competent person risk assesses the situation and provides proper advice; those who are not competent sometimes test and test again, following guidelines in a robotic and uneducated way. Asbestos is a killer – but we must target our understanding and resources properly. We must risk assess and control the real risks properly.

Martin Stear is a chartered occupational hygienist and registrar of the Faculty of Occupational Hygiene, BOHS



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