Phase contrast microscopy (PCM) analysis (NIOSH method 7400) is a technique used for determinations of airborne particulate aerosols like dust characterizations, enumeration of airborne asbestos fibres or fungal spores and airborne mould fragments. An air sample for PCM analysis is collected on a filter medium which is dissolved during sample preparation so that the collected particulate can than be viewed under the microscope.
The PCM analysis is fast and inexpensive and can be performed on site during asbestos removal operations for fast turnaround. Inability to distinguish between the asbestos and non-asbestos fibres is the main disadvantage of PCM. Therefore all fibres that meet the counting criteria are counted as asbestos fibres. Where precise determining of airborne asbestos fibres is needed transmission electron microscopy (TEM) should be used. Air sampling for the determination of airborne asbestos and phase contrast microscopy analysis is fully described in the US NIOSH analytical method 7400.
