This paper concentrates on the characterization of the heat flow present during flame cutting of 60 mm thick steel (S355N) flanges, a typical size used in the fabrication of bridge girders. Experimental results are associated with a finite element analysis of the process. Temperature measurements around the flame and extensions of the fusion and heat affected zones are used to determine the input parameters of a 3-D thermal model of flame cutting. For the sake of simplicity, the volumetric heat input within the plate is modelled using only two parameters. The heat loss associated with the air gap that forms behind the flame is adjusted to reproduce the measured cooling curves. Such a thermal model is the first step in a better understanding of thermally induced stresses during flame cutting.