The evolution of major coal oxidation and resulting sponcom incidents are sudden and may result in catastrophic negative safety outcome or result in the withdrawal of persons and closure of longwall panels/mines. Historically, experiences of highly gassy longwall workings in Australian Goonyella Middle (GM) seam (late-1990's to mid-2020's), increasing trend in CO levels and associated coal oxidation and sponcom indicator gases and related incidents due to oxygen ingress on maingate side was the major safety issue. The original Australian active longwall goaf gas drainage system designs are based on the historic work of CSIRO, supported by the operational experiences.
Over two decades ago, active goaf gas drainage flow rates were moderate (2,000 l/s to 3,000 l/s) and the oxygen ingress on TG side was not a major concern. However, with increasing goaf gas drainages rates and manual or automated mode operation of goaf wells to extreme flow rates to address higher longwall goaf gas emissions, TG oxygen ingress and air wash zones became a major issue recently, necessitating the introduction of TG inertisation strategies now to address this emerging issue. Introduction of MG proactive inertisation strategy had ultimately reduced the number of high CO or intensive oxidation incidents over two decades. This paper provides practical safety benefits of longwall tail gate (TG) inertisation supported by the original computational fluid dynamics (CFD) modelling studies carried out by the CSIRO. The field verification with both MG and TG inertisation using proactive N2 injection during various phases of longwall production and stoppages in an active longwall provides reasonable technical and operational justifications on gas and sponcom management strategy for worker's safety.
