The object of this study is coals of different stages of metamorphism and the volatile products of their thermal decomposition. Currently, based on the basic genetic signs of metamorphism, there is no reliable regulatory framework for determining the hazardous properties of mine plastics, including the propensity of coal for spontaneous combustion. Difficulties in systematization consist in the absence of at least one classification parameter, which determines the need for an additional analysis of the physicochemical properties of coals of different stages of metamorphism and the volatile products of their thermal decomposition as an object of study. Thanks to the obtained functional dependences characterizing the elemental composition of fossil fuels in the entire range of a series of metamorphism, it is possible to evaluate the classification indices of fossil fuels. The result shows that changes in the properties of coal as a result of transformations of the internal structure can take maximum or minimum values. It is impossible to judge the change in the properties of coals from the elemental content of these components by the monotonous and one-sided changes in the components С0, О0, and N0. The nature of the dependence of Н0 on Vdaf and specific gravity (Kd) suggests that coals acquire new properties after Vdaf decreases by less than 30–25 %, and specific gravity at Kd> 1.3 It is noted that coals with the same properties can in some cases be characterized by different values of the classification indicators (Vdaf Cdaf, Kd), in others–- coals with different values of the classification indicators have the same properties. The changes in the physicomechanical and calorific value of coal from Vdaf and Сdaf are complex and ambiguous. This is indirect evidence of changes in the internal structure of coals in the process of their geological transformation. The restructuring of the internal structure of coal led to a change in their electromagnetic characteristics. It is proposed, when establishing the propensity of coal for spontaneous combustion by genetic and technological parameters, to use modern knowledge in the field of geology, historical geology and paleontology, physics, chemistry, thermodynamics, as well as experience in the industrial use of coal.