Investigation of the dependence of physico-chemical and fire hazard properties from the chemical structure of alkanals are carried out. Forecasting the boiling temperature, the flash point, the temperature and concentration flammability limits o, the heats of combustion and vaporization is performed by the rules of the carbon chain. For the convenience of practical application of the rules of the carbon chain, the following empirical equations for the calculation of physico-chemical and fire hazard indices from the conventional carbon chain and from the number of carbon atoms are proposed. A comparative analysis of the proposed methods for calculating the flash point and the methods of GOST 12.1.044-89, Mendeleev and ACD/Lab 2014 is carried out. It is shown that the new methods basically give more accurate calculation results than the comparison design procedures.