This paper summarises the approach taken in establishing and validating the stall zone of a main axial fan for an underground expansion project. The expansion of an operating underground bord and pillar mine required the use of a second fan in parallel at the start of the development project. To improve the level of confidence in the ventilation simulation model that incorporated an existing fan curve provided by the fan supplier necessitated an independent fan test. Therefore, performance and stall characteristics of the current fan and pressure-quantity (PQ) survey of the mine was conducted and the results were used to calibrate the ventilation simulation model. The main axial fan was tested through a range of operating points beyond the currently perceived pressure stall point of 2.1 kPa. A pitot traverse was conducted for two operating points and the remaining operating points were measured on fan instruments. This paper details the test procedures and instruments used to collect and analyse data, and the theory used in analysis and to calibrate fan differential pressure flow measurement instruments. The fan test study has validated the fan curves with different pitch setting for use in ventilation simulation studies with twin fan installations operating with the fan pitch set to 17.5º, which is to give a good operating safety margin from the stall zone of 2.6 kPa.