A pre-flashover fire is very different from a post-flashover fire. The main difference is that in a pre-flashover fire the gas temperature and the radiation temperature differ. One thing that makes it a lot different is that the thermal exposure induced by a pre-flashover fire is largely affected by the smoke gas layer. These smoke gases can be very hot and therefore they emit heat radiation to their surroundings. The theory used, to calculate the thermal exposure of a pre-flashover fire, in this thesis relies on using thermal resistances to describe the heat transfer from the smoke gases. By doing so it is possible to calculate the temperatures of the smoke gases and the surfaces in touch with the smoke gases. Another approach is to use CFD software to numerically calculate the temperatures and in this thesis the two-zone model are compared to FDS, a CFD software. The two-zone model are also compared to a reduced-scale test. The comparisons gave good results, the two-zone model produced similar results compared to re reduced-scale test and FDS. This method of calculating thermal exposure can thereby be used to evaluate evacuation safety and save a lot of calculation time compared to calculating the thermal exposure with CFD software such as FDS.