Asbestos analysis methods: PLM, SEM-EDS, TEM and XRD

Asbestos analysis methods combine a microscope that makes the fibres visible with a measurement that reveals the mineral's chemical composition or crystal structure. The most common methods are polarised light microscopy (PLM), scanning electron microscopy with elemental analysis (SEM-EDS), transmission electron microscopy (TEM) and X-ray diffraction (XRD). For building material samples, PLM and SEM-EDS are the most common. Onelab analyses material samples with a JEOL SEM-EDS electron microscope in accordance with ISO 22262-1.

This article compares the methods at a general level: what each one sees, what it is used for and where its limits lie. An overview of what an asbestos analysis is can be found in the article what is an asbestos analysis, and Onelab's instrument is described in more detail on the page asbestos sample analysis.

What does an analysis method need to establish?

Identifying asbestos is a chain of three questions. The methods differ in which of them they can answer.

1. Are there fibres in the sample? Finding fibres requires enough magnification and resolution.
2. Are the fibres asbestos? Fibrous particles also occur in asbestos-free materials, so shape alone is not enough. Information on composition or crystal structure is needed.
3. Which type of asbestos? The six asbestos types differ in chemistry and structure. They are described in the article serpentine and amphibole.

Examining a material sample is also different from examining an air sample. A material sample shows whether a building material contains asbestos. An air sample is used to count how many fibres there are in the air.

Polarised light microscopy (PLM)

A polarised light microscope is a light microscope in which the sample is examined in polarised light. Minerals are identified by their optical properties, such as shape, refractive index, birefringence and extinction. Dispersion staining is often used as well: the fibres are immersed in a liquid of known refractive index and the mineral is identified from the coloured fringes around them.

• Use: the traditional core method for asbestos analysis of building materials. The main method in ISO 22262-1 is polarised light microscopy with dispersion staining. The standard also allows identification by SEM or TEM electron microscope with elemental analysis, and an electron microscope may be needed when the fibres are too thin for a light microscope or the binder clings to them too tightly.
• Strengths: an established and widely used method that allows the whole sample to be scanned quickly.
• Limits: the resolution of light limits the detection of very thin fibres. Bitumen, plastic and other binders can hide the fibres, in which case the sample must be pre-treated. Identification relies on optical observations, so the analyst's experience matters a great deal.

Phase contrast microscopy (PCM)

A phase contrast microscope is a light microscope that has been used to count fibres in air samples. The fibres counted on the filter are those that meet the WHO fibre definition: longer than 5 micrometres, thinner than 3 micrometres and with a length-to-width ratio greater than 3:1.

• Use: fibre counting in air samples.
• Limits: the method does not distinguish asbestos fibres from other fibres and cannot see the thinnest fibres. That is why fibres in air samples must be counted with an electron microscope from 21 December 2026. Read more on the page the 2026 asbestos law change.

SEM-EDS: scanning electron microscope and elemental analysis

A scanning electron microscope (SEM) images the sample with an electron beam instead of light. The image shows the shape and proportions of a fibre even when the fibres are too thin for a light microscope. An energy-dispersive spectrometer (EDS) attached to the instrument measures the X-rays generated in the fibre, which give its elemental composition.

• Use: both material and air samples.
• Strengths: shape and chemical composition are obtained from the same fibre. Based on the composition, asbestos is distinguished from other fibres and the six asbestos types from each other.

TEM: transmission electron microscope

In a transmission electron microscope (TEM), the electron beam passes through a very thin specimen. The instrument can see even the very thinnest fibres. Electron diffraction reveals the fibre's crystal structure, and an attached EDS gives its composition.

• Use: mainly air samples, dust samples and specialist investigations.
• Strengths: the highest resolution, with crystal structure and composition obtained from the same fibre.
• Limits: sample preparation is more laborious than in the other methods, and TEM is less common in routine analysis of building materials.

XRD: X-ray diffraction

In X-ray diffraction (XRD), a ground-up sample is exposed to X-rays, and the crystal structure of crystalline minerals is identified from the diffraction pattern they produce.

• Use: determining mineral composition, for example when examining aggregates and industrial minerals.
• Limits: XRD does not show particle shape, so it cannot tell a mineral's fibrous asbestos form from its non-fibrous form. Small amounts can be hard to detect among other minerals. XRD is therefore a supplementary method and not sufficient on its own for asbestos analysis of building materials.

Why does Onelab use a JEOL SEM-EDS electron microscope?

Onelab analyses all material samples with a JEOL SEM-EDS electron microscope. The reasons are practical:

• The instrument shows thin fibres that are hard to make out with a light microscope.
• Elemental analysis distinguishes asbestos from other fibres and identifies all six asbestos types.
• The same instrument is suitable for both material samples and air samples.
• The analysis follows ISO 22262-1, and the result is sent by email, typically on the day the sample arrives.

Onelab is a laboratory that analyses samples customers take themselves and send in by post. On-site asbestos surveys are handled by our sister brand AsbestiPro.

A method cannot fix a poor sample

Even the most accurate method cannot find asbestos that is not in the sample. The sample must represent the material you plan to remove or work on, and it must include every layer.

When sampling, wear disposable gloves and a respirator of at least class FFP3, mist the spot, remove a piece of about 2–5 centimetres through all the layers, pack it in two zip-lock bags and mark the bag with the sample location. Finally, cover the spot with tape and wipe the area with a damp cloth.

More detailed instructions are in the article how to take an asbestos sample, and choosing the number of samples is covered in the article how many asbestos samples you need. Reading the result is explained in the article interpreting an asbestos result.

How much does an asbestos analysis cost?

The analysis costs €39.90 + VAT per sample, and the price is the same for 1–100 samples. Orders of more than 100 samples can be priced separately. Postage is not included. You can order the analysis online and send the sample to the laboratory by post.