This standard specifies the membrane filter method for determining the concentration of airborne asbestos fibres in a work environment. It details the procedure for collecting air samples, preparing the sample for analysis, and counting fibres using phase-contrast light microscopy. The method is crucial for monitoring occupational exposure to asbestos and ensuring regulatory compliance.
Method for Determination of Airborne Asbestos Fibre Concentration in Work Environment by Light Microscopy (Membrane Filter Method)
Quick Reference Values
Countable fibre length> 5 µm
Countable fibre width< 3 µm
Countable fibre aspect ratio (L:W)> 3:1
Microscope magnification for counting400x to 500x
Membrane filter nominal pore size0.8 to 1.2 µm
Recommended sampling flow rate0.5 to 2.5 litres/min
Key Formulas
C = (A / a) * (n / V) — Formula for calculating fibre concentration in air, where C is concentration, A is effective filter area, a is graticule area, n is mean fibre count, and V is volume of air sampled.
Practical Notes
This method is not specific to asbestos; it counts all inorganic and organic fibres that meet the dimensional criteria. For positive identification of asbestos, more advanced techniques like Transmission Electron Microscopy (TEM) are required.
The accuracy of the result is highly dependent on the skill and experience of the analyst performing the fibre count. Regular training and inter-laboratory checks are essential.
Proper calibration of the air sampling pump's flow rate before and after sampling is critical for an accurate calculation of the total air volume and final fibre concentration.