Monte Carlo simulations of image generating stray processes in SEM measurements of fibres

  • Project number: F 2469
  • Institution: Federal Institute for Occupational Safety and Health (BAuA)
  • Status: Completed Project


Even so-called inert dusts that do not pose a direct chemical hazard can endanger the health of employees. Of particular concern are thin and long fibres which, when inhaled, can accumulate in the lung tissue and cause chronic inflammation. Limit values have been set to protect employees from such risks. To monitor these limits, it is necessary to be able to measure the diameter of fibres sampled from the workplace air with high accuracy.

German testing laboratories use electron microscopes for such measurements. The dimensions of a fibre are determined from brightness contrasts of its electron microscope image. The software developed in the project can simulate the physical scattering processes that govern the generation of images with an electron beam directed at a sample in the microscope (Monte Carlo method). By systematically comparing real and simulated electron microscope images of fibres of different thicknesses, it is possible to determine the measurement accuracy as a function of diameter and composition.

This provides a solid physical basis for investigations to monitor occupational exposure limits or to justify regulatory decisions based on particle and fibre dimensions.

The project was carried out in collaboration with the German National Metrology Institute PTB (Physikalisch-Technische Bundesanstalt) in the field of length metrology using microscopic methods.

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