Abstract: A system and method for automated analysis of a membrane filter obtained from an air quality monitoring apparatus used for sampling airborne respirable fibres such as asbestos and synthetic mineral fibres is described. The system comprises capturing a macroscale image a membrane filter and analysing macroscale image using a computer vision method to determine a countable area of the membrane filter and one or more excluded regions within the countable area of the membrane filter. These excluded regions comprise membrane filter grid lines, air bubbles and large particulate matter. The slide is then placed on a robotic XY stage of a digital phase contrast microscope which is used to capture at least one magnified phase contrast image at each of 20 or more sample locations located across the filter member. The sample locations are selected such that a field of view at each sample location does not contain an excluded region.