Air monitoring techniques could be responsible for reported differences in the asbestos fibre levels found at Cwmcarn High School in Caerphilly, which was temporarily closed in October 2012 and all 900 pupils transferred to another school.

Following the discovery, a national audit of asbestos in Welsh schools was called upon and Education Minister, Leighton Andrews, asked for all schools to deliver reports on their asbestos levels. Previous surveys undertaken by the Health & Safety Executive (HSE) have found that there is still a lack of asbestos awareness by hundreds of schools to the existence of asbestos-containing materials and also a failure to comply with safety management procedures.

According to an initial survey, it was claimed that there was between 0.003 and 0.008 fibres per millilitre, or ‘ten times’ the accepted fibre level.

However, according to The Control of Asbestos at Work Regulations 2002, the control limits for asbestos exposure for white asbestos (chrysotile) are:

(a) 0.3 fibres per millilitre of air averaged over a continuous period of 4 hours.
(b) 0.9 fibres per millilitre of air averaged over a continuous period of 10 minutes.

(ii) For any other forms of asbestos, such as blue ( crocidolite) or brown (amosite) either separately or combined with any asbestos types:

(a) 0.2 fibres per millilitre of air averaged over a continuous period of 4 hours.
(b) 0.6 fibres per millilitre of air averaged over a continuous period of 10 minutes.

Subsequent HSE investigations carried out by the Health & Safety Laboratory indicate that the previous tests could “overestimate the levels of asbestos fibres as it does not distinguish between asbestos fibres and other fibres such as paper, clothing and skin cells”.

Conventional air monitoring techniques are designed to collect all airborne fibres above a minimum size from a known volume of air via a filtering method. While all airborne fibre levels might be established, they are ultimately an imprecise measure to determine the specific presence of asbestos fibres.

Whenever a release of airborne asbestos material is suspected, it is vital to carry out a technique known as ‘fibre discrimination’, which will precisely separate and quantify asbestos from non-asbestos fibres present.

Analysis of asbestos minerals includes identification of:
(i) Long fibre-forming bundles
(ii) Fibres split into finer strands
(iii) Chemical composition

The asbestos minerals can be identified using several methods. Previously, samples would need to be collected and sent to a laboratory to be analysed using, for example, transmission electron microscopy (TEM), X-ray diffraction (XRD) or infra-red spectroscopy (IRS).

However, it is now also possible for portable on-site evaluation to be undertaken using phase contrast polarized light microscopy (PLM). By this method, asbestos fibres can be identified by their refractive index as well as appearance and optical properties and ‘phase contrast’ microscopy for fibre counting.

Once asbestos fibres are inhaled, they can permanently embed in the linings of the lungs, which over a period of between 15 to 50 years can cause asbestosis disease or the incurable mesothelioma cancer.

The HSE estimate that there could be around four million properties in England and Wales still containing hidden asbestos material and some 1.8 million people, from builders and teachers to flat owners and housing estate tenants, can be exposed to asbestos every year in the UK.