PCM cannot detect fibers smaller than what size?

Phase Contrast Microscopy (PCM) is a widely used method for counting asbestos fibers in bulk samples and air samples. A key limitation of PCM is its ability to detect fibers of a certain size; specifically, it is unable to reliably identify fibers smaller than 0.25 microns in diameter.

Fibers that are below this size threshold may not be counted accurately due to the resolution limits of the microscopy technique employed. As a result, PCM is not suitable for detecting ultrafine asbestos fibers that can pose health risks, particularly since these smaller fibers can be more easily inhaled and retained in the lung tissue.

Larger fibers, such as those 0.5 microns and above, are within the detection capabilities of PCM. Thus, knowing this threshold is critical for professionals involved in asbestos monitoring and site surveillance, ensuring they choose appropriate testing methods based on the types of fibers that need to be detected.