Abstract: Thermal radiation is the dominant mode of heat exchange in indoor fires, and it is of great significance for studying the flashover mechanism. By analyzing the radiant heat transfer processes of vertical flames, hot smoke layers and lining materials, a theoretical model of multi-surface radiant heat transfer in indoor fires was established, and the mathematical expression of the radiant heat flux received by combustibles at the floor center was derived. The influence of radiant heat transfer processes in indoor fires on flashover occurrence was explored, and the theoretical model was verified and modified through small-scale experiments. The results show that only 0.2% to 2.0% of the heat radiated by the flame located at the corner reaches the center of the floor, which is less than 0.7% in most cases, indicating that the radiation effect of vertical flames on combustibles horizontally placed on the floor is negligible. The prediction accuracy of the modified theoretical model can reach 80% before flashover occurs. Combined with the radiant heat flux criterion at flashover, the height of the smoke layer interface when flashover occurs can be predicted.

Key words: indoor fire, flashover, radiant heat transfer, flame, smoke layer