OFFICIAL Figure 9:summarises the results from the ARC iso-aging test commenced at 45 °C where no heat was lost from the sample and the isothermal test where the temperature was maintained at 55 oC until a reaction was detected. It is clear from Figure 5 that when heat is not dissipated from the system, self-heating reduces the time to thermal runaway. Although blastholes are not perfectly adiabatic, typical reactive ores and bulk explosive products have low thermal conductivity, which limits the capacity to dissipate heat (Rumball, 1991). In practical terms most blast holes will be somewhere between the high thermal conductivity environment of the isothermal test and the adiabatic conditions in the ARC. Given the high potential consequences of unplanned detonation, adiabatic results provide a credible worst-case model. However, adiabatic testing is not widely available and there are decades of isothermal reactive ground testing data that has proved simple and effective in identifying reactive ground and qualifying suitable products. The isothermal test has been effective because of the safety buffers built in with respect to test temperatures and durations. The innovation of the current approach is quantifying the impact of the inhibiter to allow the inhibitor budget to be used as an additional factor of safety. The proposed protocol prioritised using existing global testing networks and expertise while having a reasonable turnaround time and robust factors of safety. It was decided that the standard 28-day test was a suitable starting point. A two-stage process was adopted, an initial screen to rank reactive samples as high risk or low risk. Low risk results qualify Orica’s Marathon i TM product range for the 90-day sleep time. High risk samples are tested further against a range of inhibitor levels and the full dataset of the specific sample used to extrapolate to a safe inhibitor level at 90 days. Significant
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