AbstractThe purpose of this work was to examine the phenomena which determine the possibility of flashover occurrence and progress in compartment fires. A number of experimental fire tests were performed aimed at simplifying the phenomenon in successive tests by eliminating the factors influencing the main mechanisms which determine the occurrence of flashover in compartment fires. A physical model has been proposed as well as mathematical description of the flashover, including a simplified first stage of fire development. A new method for mathematical description of chemical mechanisms of combustion in gas mixture was employed according to which the experiments were considered to be simplified kinetic tests permitting the derivation of a substitute formula for chemical change. A computer program was developed enabling computation of the dynamics of the pre‐flashover fire phase. By means of this program, extensive theoretical analysis was performed of the influence on fire development of a number of compartment factors, including fire load, ventilation and potential fire siz