The analysis of the dynamics of the corrosion processes of the lining and concrete trunk of the chimney, depending on the operating conditions and climatic conditions, reveals the conditions for the formation of initial cracks in the lining, the dynamics of their growth, it is shown that, with a density of hair cracks of 10 pieces on an area of 0.5 m2, so permeable that the rates of local corrosion processes of lining and concrete materials create an excessive risk of destruction of the chimney. Especially quickly the degradation processes the chimney is exposed at a point about one-third of the top at gas velocities below 10 and above 20 m/s. Excessive permeability of the lining as an additional critical defect is suggested to be taken into account in the composition of critical defects in the traditional classification of their hazards, and its identification is to be based on the results of recognition of defects in photographs obtained by monitoring the chimney with an autonomous device — by the parameter “exceeding the density of cracks by opening width 1 mm and more than 10 pieces on an area of 0.5 m2. At the same time, in the analysis of the risk of destruction of the chimney, the event tree is complemented by the fourth branch, which means the emergence of a critical defect — excessive permeability of gases through the lining. In addition, the lengths of cracks in the lining and concrete trunk are referred to the diameter of the pipe, which makes the classification more universal.