Asbestos fibre Counting by
Phase Contrast Microscopy

Methodology for PCM Analysis: NIOSH 7400 & OSHA ID160
Phase contrast microscopy is the method that is primarily used for estimating asbestos concentrations of airborne fibres. This method is quick and can be performed on-site for a rapid determination of concentrations of asbestos fibres in the air. Phase contrast microscopy does not positively differentiate between asbestos and other fibres. Positive identification of asbestos fibre must be performed using PLM (Polarized Light Microscopy) or Electron Microscopy (Method 7402)

Required Microscope Equipment
Positive phase contrast microscope with 10X Brightfield and 40X Phase objectives, GIF (Green Interference Filter), Walton & Beckett reticle Type-22G and a stage micrometer with 0.01mm divisions.

Required Test Slide
The HSE/NPL Mark II Phase Shift Test Slide checks or standardizes the visual detection limits of the phase contrast microscope. The HSE/NPL Test Slide consists of a conventional glass microscope slide with seven sets of parallel line pairs of decreasing widths. The microscope must clearly resolve line pairs 1 thru 3. Line pairs 4 and 5 must be at least partially visible. Line pairs 6 and 7 must be invisible. A microscope which fails to meet these requirements is either too low or too high in resolution and cannot be used for asbestos detection.