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The results of experimental study of wall-free non-stationary fire vortices are presented. The generation of vortical structures occurred by the burning of pellets of urotropine (hexamethylenetetramine) located on the underlying surface (sheet of aluminum). Unlike most previous research experiments the mechanical twisting devices and the shear air stream to get fire vortex structures were not used. It was assumed that the generation of fire whirls occurred due to the instability of the combustion process. Experimental data on the conditions of fire whirls generation (number of pellets, generation start time and thermal power) and their integral parameters (life time, height and diameter) have been received.