A B-RISK produces modelling outputs in a format that fire engineers will be able to compare against probabilistic statements of building performance. The Design Fire Generator is one of the modules within the overall B-RISK model, which creates a unique probabilistic design fire. The design fires generated for an open plan single workstation and for multiple workstations in compartment are compared with NIST experimental results. The design fire inputs are created in the form of heat release rate (HRR) time histories that are generated by the DFG. This paper compares the HRR of commercial scale occupancies; item-to-item fire spread sequences and its time line of DFG output of B-RISK modelling with experimental results.