Abstract The paper deals with problematic of fire experiments connected to Flashover phenomena. Real 3D experiments in small-scale need to be preparated in sence of exactness by exact calculations. The thermocouples are installed in three layers horizontally, and in five layers vertically. The heat flux of 15 or 20 kW.m –2 need to be reached to reach the flashover condition. After that the 600 °C can be reached as a minimal temperature and open fire escapes through the open vents. The measurements by Almemo station are continuously made, than data are to be statistically interpreted and conclusions are made.