Rio Tinto Coal Australia (RTCA), Queensland Mines Rescue Service (QMRS) and Simtars conducted a partial inertisation of an underground coal mine using the GAG-3A engine in February 2014. This was an ACARP funded project No C23006. This project monitored the environmental conditions and the flow of inert GAG gases into and around the mine. Observations were made by a variety of remote sensing technologies and by direct measurements as well as observations made by mines rescue personnel in the inertised area. This paper documents methodology, observations and the outcomes including a review of previous inertisations. This project proved that the GAG is a reliable and effective inertisation system. It demonstrated the critical requirement for effective sealing of GAG docking points. It is not envisaged that the GAG could be deployed where there is an expectation that mine personnel could be in the vicinity as temperatures of 90°C were measured. Mine infrastructure and strata in zones close to the GAG docking station were detrimentally affected by prolonged exposure to the high humidity and temperature.