[Air concentration of asbestos fibers at work sites]

The paper presents a method for measuring the concentration of asbestos fibres at workplaces. This method consists in sampling the dusted air onto membrane filters, making the filters transparent and counting asbestos fibres under an optical microscope with a positive phase contrast. Errors in counting asbestos fibres, sampling and precision of the method were discussed (total error of the method). Measurements of the concentration of asbestos fibres in the air at workplaces were made at plants producing asbestos textile products, seal plates, packings and frictional goods. 0.1 fibre/cm3 was the lowest concentration (sensitiveness of the method).