The study focuses on investigating models for calculating the risks of fire spread from an industrial building to adjacent buildings. The basic parameters necessary to determine the risk of fire spread are the flame height and the incident heat flux. There is limited information found about flame heights from industrial buildings where the fire breaks through the ceiling. Calculation methods for flame heights and incident heat fluxes are discussed and compared to model-scale data and large-scale data. A series of model-scale tests with flames through openings in a building where flashover has occurred are presented and compared to flame height correlations. This paper provides new data and a better understanding of the necessary input for such calculations. The model-scale tests show a good correspondence between a simple method to calculate heat flux from a point source and experimental data.