The number of organic compounds exceeded 40 million and increases each year by 300 thousand. To ensure the fire safety and technological calculations of processes of production, for storage and transportation materials there are needed data rates fire and explosion hazard substances. Therefore, development of a method of forecasting fire danger indicators and thermodynamic properties of substances, based on the minimum amount of experimental data, is an important task. Solution of this problem is connected with an establishment of the relationship between the molecular characteristics and thermodynamic properties of substances in the homologous series. The available methods for calculating the properties of multi component systems are also based on the properties of the constituent components. An essential drawback thermodynamic value of standardization methods is that the obtained values of the thermodynamic functions are only indirectly related to the intermolecular interaction that determines the properties of liquids. It is known that the laws of thermodynamics do not contain the concept of interaction. These concepts are introduced from other areas of science. The interaction energy of the molecules is defined as the work of their division into an infinite state. However, another possible solution to the problem - isolation of molecules from interacting with each other, while maintaining the distance between them. If the energies of the “isolated” and “separated” molecules are equal, off the intermolecular interactions in the two cases, require the same work. Contribution of intermolecular interactions in the thermodynamic function is determined by the difference between the values of this function for the standard and the actual systems. As a standard system without intermolecular interaction was taken ideal gas at the temperature and volume of liquid. As objects of research are chosen substances of the homologous series of n-alkyl amines. The analysis determined that values of the thermodynamic functions of substances additively depend on the molar weight of n-alkyl amine in the homologous series. Similar dependence was observed for the flash point n-alkyl amines. Taking into account the general tendency in the change of flash point values and the Helmholtz energy of molar weight substances in the homologous series, it seems appropriate to establish their interrelation. The corresponding equations were obtained. Earlier similar dependence was observed for the homologous series of substances: n-alkyl etanoats, aliphatic ketones and alcohols. The established regularities and obtained based on these equations allow us to predict the properties of homologous series of substances with the necessary accuracy for practical purposes.