In the Emanation Thermal Analysis the release of inert gas atoms previously incorporated in the sample is measured. Results
of the statistical modelling of the inert gas release during thermal decomposition of solids are presented. The updated model
supposing three components in the solid-state reaction system including the formation of an intermediate metastable component
on the surface of the newly formed component was proposed for the modelling of the ETA curves. The release of inert gas atoms
previously incorporated into the sample is used as a probe of microstructure changes. The random nucleation mechanism was
considered in the modelling. The model can be used in modelling ETA curves of solid-solid, solid-gas and solid-liquid interactions
where the existence of metastable intermediate component is supposed.