In the event of fire, intumescent coatings experience several reactions that cause the foaming and swelling of the material. As a result, a cellular char with low thermal conductivity is formed. This material has been widely employed as a passive fire protection for steel elements in buildings and industrial platforms. Several studies suggest that the insulation performance of the final char is highly related to the pore morphology (e.g. porosity, pore size and shape distributions). Thereby, conducting a quantitative analysis of its internal structure can provide valuable insights into the performance of intumescent coatings.

Microscope images demonstrate the high interconnectivity among pores within intumescent coating chars. The challenge arises during the specification of the boundaries between these pores, where the definitions remain unclear. The watershed algorithm is a popular technique for partitioning the pore space. However, it tends to over-segmentate long elliptical pores, which are common in intumescent coating chars.

In this work, a refined algorithm has been designed to solve this challenge. It uses the watershed method combined with the simulation of intrusion techniques to effectively find the pores. The results show the method´s capability to measure pores ranging from 1 μm to 8 mm with different shapes, highlighting its versatility for applications in diverse porous materials. It emerges as a promising tool for investigating the intumescent char growth under various conditions or exploring potential modifications to its structure.