The invisible threat: fibres below 0.2 µm
Standard asbestos exposure assessments rely on Phase Contrast Microscopy (PCM), which can only resolve fibres with a diameter of approximately 0.2 µm or greater. This means that a significant fraction of airborne asbestos fibres — those thinner than 0.2 µm — are systematically excluded from fibre counts, even though they are present in the air and can be inhaled deep into the lungs.
The RIVM literature review, commissioned by the Dutch Ministry of Social Affairs and Employment, found clear evidence that these ultrafine fibres contribute to asbestos’s harmfulness. However, the authors note that it is not yet possible to precisely quantify the additional risk they pose, due to limitations in existing epidemiological and toxicological data.
Why TEM matters: the only technology that sees everything
Transmission Electron Microscopy (TEM) operates at magnifications and resolutions far beyond what optical microscopy can achieve. While PCM has a practical detection limit around 0.2 µm diameter, TEM can resolve fibres down to the nanometre scale — making it the only analytical method capable of detecting the full spectrum of asbestos fibres present in an air sample.
Beyond detection, TEM also enables definitive identification of fibre type through Selected Area Electron Diffraction (SAED) and Energy Dispersive X-ray Spectroscopy (EDS). This means TEM can not only find ultrafine fibres that PCM misses, but also confirm whether they are chrysotile, amosite, crocidolite, or other regulated asbestos types.
PCM vs TEM at a glance
PCM counts fibres by visible light and cannot detect anything thinner than ~0.2 µm. TEM uses an electron beam and can resolve fibres down to the nanometre scale, while also identifying fibre mineralogy. The RIVM findings confirm that PCM-based assessments systematically undercount asbestos exposure.
Find a laboratory with TEM capability near you
If you need asbestos analysis that goes beyond PCM — especially for projects involving sprayed coatings, insulation boards, or severely degraded fibre cement — TEM analysis is the only method that can detect the full range of asbestos fibres, including those below 0.2 µm.