Phase contrast microscopy is the standard method used for the sampling and counting of fibres in the air. The basic process entails air being drawn at a known flow rate through a filter for a measured time, which results in the collection of airborne particles.
This is followed by the filter being mounted on a glass slide and rendered transparent, thereby enabling microscopy examination. PCM of at least 500x magnification is used to examine a known fraction of the filtered deposit. This enables the counting of all fibres seen in a known number of microscope graticule areas.
Then, it will be time for the fibre concentration to be determined, in terms of fibres per millilitre of air. This is done by dividing the total number of fibres collected on the filter’s exposed area by the volume of sampled air.