Analysis of mine fire growth and spread is important for improving safe emergency egress for mine workers in fires. In fire engineering, a ‘design fire’ is the term that describes the characterisation of a fire in relation to its growth and decay. Defining the design fire is the starting point for managing the fire risk of a mine and is the basis for further analysis of emergency response. A current Minerals Industry Safety and Health Centre (MISHC) PhD project is researching methods of improving fire life safety and asset loss control in mining using Video Based Fire Detection (VBFD) in the context of fixed plant fires. Experiments were carried out at Safety in Mines Testing and Research Station (SIMTARS) facilities. This research was part of the MISHC project to better understand the detection capabilities of VBFD in relation to weak plumes from the early combustion of coal associated with fixed plant. This part of the research specifically deals with assessing the physical dimensions and shape of the low energy, non-flaming weak plumes formed from smouldering coal fires. It demonstrates how experimental methods were used to successfully validate the corresponding numerical simulation of the design fire so it can be used for further research.