Phase Contrast Optical Microscopy (PCOM)
Definition
The WHO-recommended routine method for counting airborne asbestos fibres in occupational and environmental samples; counts fibres visible at 400-500x magnification, with confirmation of mineral identity requiring electron microscopy.
- Recommending body
- World Health Organization
- Application
- Airborne asbestos fibre counting
- Magnification
- 400 to 500x
- Limitation
- Cannot confirm mineral identity, needs electron microscopy
Common questions
Why can't PCOM identify whether counted fibres are actually asbestos?+
PCOM counts any fibre meeting the size criteria based on visible shape and dimension, but its resolution and contrast mechanism cannot distinguish asbestos minerals from other fibrous materials, so mineral confirmation requires electron microscopy with elemental analysis.
How is a PCOM fibre count actually used in practice?+
The count against a defined volume of sampled air gives a fibre concentration used to assess occupational or environmental exposure against regulatory limits, while separate electron microscopy analysis is reserved for cases needing confirmed mineral speciation.
Related terms
- Asbestos
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- Fly Ash
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- Geoforensic Location Indicator
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- Manufactured Mineral Fibre (MMF)
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- SEM-EDX
- Scanning electron microscopy with energy-dispersive X-ray spectroscopy. The electron beam excites characteristic X-rays from each element present in the target grain, giving...