Asbestos - a journey of discovery

Kerry Taylor-Smith left Lab News Towers for sunny Somerset to investigate the world of asbestos analysis. Aided by her dad Andre and G&L Consultancy she embarked on a journey of discovery - not only about the analysis of this potentially deadly substance - but also the hidden talents of her dad.

When my dad first started reeling off terms like refractive index, birefringence and pleochroism I was suitably impressed – my GCSE chemistry had failed me and I couldn’t remember what half of these terms meant – but there he is with 20 years on me, memorising their definitions as revision for his BOHS P401 (British Occupational Hygiene Society) exam to become a fully-trained asbestos analyst.

Eighteen months later, and I got to spend a day shadowing him as he went about his work at G&L Consultancy in Creech St Michael, Somerset – and I was still impressed! My dad – never one to blow his own trumpet – has always maintained he was never very scientific at school: I think he steered clear of science after he almost set fire to his bedroom with his chemistry set when he was 10, but a job like this requires a high level of knowledge; you’ve got to know what you’re looking for, how to analyse it and dispose of it safely.

Asbestos is a deadly material – it can cause lung cancer and asbestosis if inhaled, but because of its flexibility, high tensile strength, incombustibility and low thermal conductivity it was used as insulation in buildings, in ceiling and floor tiles, even in toilet cisterns for many years. When the Twin Towers collapsed in September 2001, it is believed that over 1000 tonnes of asbestos was released into the atmosphere and could be responsible for the unusually high death rate among rescue workers involved in the operation.

Health and safety – and cleanliness – are of the utmost importance in the lab. For these reasons, each lab has to be accredited by the United Kingdom Accreditation Service (UKAS) to the ISO17025 standard before it can carry out bulk analysis of asbestos samples. Each year the whole company is audited by UKAS to ensure that the proper processes and procedures are being adhered to. Last year having just qualified, my dad was chosen as lab representative to undergo questioning.

“It’s quite nerve-wracking and because I was the newbie in the lab it was my turn,” he said, “But it’s important that the company is checked to ensure we’re doing everything properly.”

[caption id="attachment_36041" align="alignright" width="200"] 1a: Chrysotile under a stereo microscope x20 magnification 1b: Chrysotile under a polarised light microscope x150: looking for angle of elongation 1c: Chrysotile under polarised light microscope x150; looking at the dispersion staining[/caption]

When we first entered the lab – obviously once I had been introduced to everyone – my dad showed off his certificates on the wall, and then his workstation; a stereo microscope contained in a glove box, pestle and mortar, petri dish, tweezers etc. And then we set about to work. Even though the workstation was thoroughly cleaned the night before, my dad gave it another quick clean before finding his first sample of the day.

For safety reasons, each sample sent to the lab is double-bagged in sealed airtight bags. Each sample has a unique reference number, and comes with a Bulk Materials Analysis form and Sample Report which has to be filled out with details of what’s been found. Samples are only ever opened in the glove box, which is under negative pressure and has a HEPA filter to ensure any harmful fibres are not released into the lab. Once removed from the bag the sample is placed on the viewing dish, under the stereo microscope which is set at x20 magnification.

“Not all samples are positive, a great deal will contain no asbestos at all,” dad said, “In a positive sample we will see either straight or curly fibres. The curly fibres are chrysotile (white asbestos) – the straight fibres usually mean it’s another type of asbestos.”

The first sample we were looking at contained chrysotile – under the stereo microscope it did just look like a bunch of white fibres sticking out of a piece of cement (image1a). My dad carefully plucked a few fibres from the sample and arranged them on a slide in a cross. (You don’t need to put them in a cross shape, but it made it easier to see and to get good pictures!)

We moved across to the polarised light microscope to look for the sign of elongation, which depends on the fibre shape and its optical properties. A tint plate – a first order red compensator – is placed at 45° to the polariser, in a slow ray in the northwest to southeast direction.

Because asbestos is an anisotropic material, it has two main refractive indices which give two light ray speeds – fast and slow – which run along the length of the fibre or across it. Man made mineral fibres (MMMF) and vegetable fibres – don’t exhibit birefringence because they are isotropic and only have one refractive index and all light passes through at the same velocity.

[caption id="attachment_36047" align="alignleft" width="200"] 2a: Amosite under stereo microscope x20 magnification 2b: Amosite under a polarised light microscope x150: looking for angle of elongation 2c: Amosite under polarised light microscope x150; looking at the dispersion staining[/caption]

Peering down the microscope I saw orange-yellow fibres going top left to bottom right, and blue fibres going bottom left to top right, all on a bright pink background (image 1b).

“This is how most types of asbestos appear,” dad said, “They’re positive fibres, meaning the slow ray of light vibrates parallel with the length of the fibre and the slow ray of the tint plate.”

Only crocidolite (blue asbestos) has a negative sign of elongation, where the fast ray of the fibre vibrates parallel with the length of the fibre and the slow ray of the tint plate. If the fibres are negative, the fibres from northwest to southeast are blue, and northeast to southwest are orange-yellow.

Next we looked at the dispersion staining of the sample – this is how you can really tell what type of asbestos you’re dealing with. While preparing the slide and before adding any fibres, it was dotted with a Cargille liquid.

“To make sure you’ve got the asbestos you think you have, you put the sample in a Cargille liquid with a similar refractive index to what you’re expecting – in this case -1.550, which corresponds to chrysotile,” dad explained, “The RI of the liquid matches the RI of the fibres, so when you look at it under the polarised light microscope you get certain colours depending on the asbestos. If it’s in the wrong liquid you won’t get the correct colours.”

Chrysotile has a distinctive dispersion staining, with fibres parallel to the tint plate appearing purple, and perpendicular fibres appearing blue (image 1c). This type of asbestos is usually found in reinforced composite materials like vinyl floor tiles and window sills; corrugated cement roof sheets; asbestos textiles and insulation boards; and textured coatings like artex ceilings. The sample was then re-bagged and the viewing dish and tools thoroughly cleaned to avoid cross contamination of samples.

The next sample we looked at was from an asbestos insulation board. We placed it in the viewing dish and it was clear we had a different type of asbestos – this time amosite (brown asbestos). These fibres are straight and are quite easily spotted in the sample under the stereo microscope (image 2a).

When placed under the polarised light microscope, and checking the sign of elongation, these fibres appear the same as the chrysotile – blue and orange-yellow fibres in the same orientation on the same pink background. But under dispersion staining, we saw something completely different – the fibres from northeast to southwest were yellow, and northwest to southwest the fibres appeared purple/red.

“We used a different Cargille liquid this time,” dad explained, “We needed to use one which most closely matches the refractive index of amosite – around -1.670 – to ensure we got the right colours.”

As well as being found in insulation board, amosite is found in composite materials like toilet seats and cisterns – like the big black ones we all used to have at school.

The next sample we looked at contained crocidolite – a particularly nasty type of asbestos that is easily identifiable under the stereo microscope because of its blue fibres (image 3a). Crocidolite is the only commonly-used asbestos which exhibits pleochroism – a change in the colour of the fibre with orientation relative to the vibration of polarised light. When parallel to the plane, the fibre appears blue, but when perpendicular it appears blue-grey. Actinolite also shows pleochroism (green/grey) but this was not so widely used.

[caption id="attachment_36049" align="alignright" width="200"] 3a: Crocidolite under stereo microscope x20 magnification 3b: Crocidolite under a polarised light microscope x150: looking for angle of elongation 3c: Crodidolite under polarised light microscope x150; looking at the dispersion staining[/caption]

Crocidolite has a fast or negative sign of elongation, so when l looked under the microscope I saw blue fibres going top left to bottom right, and dull orange fibres going bottom left to top right, all on the familiar bright pink background (image 3b). With dispersion staining – using a Cargille liquid of the value -1.700 – I saw light blue from bottom left to top right and a darker blue from top left to bottom right.

Crocidolite is often found in composite materials used in toilets, and asbestos insulation boards and cement. There are also three other types of asbestos; tremolite, anthrophyllite and actinolite. These were much less widely used, and although I didn’t get to spot any on the day, they’re really only likely to have been used in asbestos insulation or coatings. The samples we looked at were all dry, and it was relatively easy to pick out the asbestos fibres under the microscope – but it’s not always that easy. Sometimes the samples have to be ground with a pestle and mortar to release the fibres, and even dissolved in 1M hydrochloric acid to remove the matrix holding the fibres. The sample then needs to be dried out before analysing.

A lot of the samples the lab receives are from council housing stock around the county, but they’ve also had samples from university buildings, ship yards, farms, clients doing housing surveys and even concerned residents worried that their houses might contain asbestos.

Bulk sample analysis is just one part of the asbestos analysis services offered by G&L Consultancy. They also provide surveys and asbestos management – after all, if you’ve found asbestos in a building, you have to take precautions by either encapsulating or removing the offending areas to ensure no-one is exposed to the dangerous material. This involves various assessments to gauge the risk presented by the asbestos, writing an asbestos management plan and providing staff training.

They also offer air monitoring – drawing a known volume of air through a filter to monitor for asbestos fibres in the air. The filter can be analysed under a microscope to check for the presence of fibres. A proportion of the filter is analysed and the number of fibres counted, when compared to the sample’s volume of air, the fibre concentration can be calculated.

Asbestos has been used in many applications – more than you might think – and it’s important to remove and dispose of the mineral safely. Just testing for asbestos in the lab is a highly involved and complex job and I was really impressed that my dad was working in this highly scientific environment – especially since he told me he was never any good at science!

See videos of chrysotile under the polarised light micrscope looking for the sign of elongation and dispersion staining recorded by Kerry and Andre under Lab News Recomments at www.youtube.com/labnews. Images in this feature can be found on www.flickr.com/laboratorynews