1963 Figure 123: Cross section of blast hole loaded with ANFO bulk product showing the temperature gradient at 0, 8 and 16 hours Figure 122 and Figure 123 show the impact of loading bulk products into a blast-hole on the system’s ability to dissipate the heat. Even at a relatively modest heat flux of 45 W/m2 reported for coal selfheating (Guo, 2024), the wall temperature has exceeded the starting condition of 70 oC after 16 hours. It was also evident that the emulsion blend was slightly better at conducting heat than the ANFO product, as evidenced by the greater wall temperature of the ANFO product and lower core temperature due to the poor heat transfer properties, though neither product could dissipate heat better than convective air in an open hole. Given reactive ground reactions start at the interface of the product with the blast-hole wall or cuttings, the wall temperature is most relevant to the safety of the system. The reduced heat transfer and potential for the product / wall boundary to increase in temperature over time was a key consideration for excluding areas with evidence of self-heating from consideration for long sleep times. 4. DISCUSSION The results of the time-to-reaction studies using both isothermal and ARC testing have been applied to develop a feasible path to extend reactive ground sleep times to 90 days, supported by scientific evidence and within practical timeframes for testing. This represents a significant advancement in blasting safety. Previously, the industry had little quantitative insight into how inhibitor levels correlate with safe sleep times beyond a 7-day horizon. It has long been known that increased inhibitor levels increased the potential sleep time, but the previous data was inconsistent and difficult to fit to correlate to a mathematical model with a good fit. It should be emphasized that the conclusions apply to ambient temperature reactive ground, i.e. rock that is stable, not self-heating and less than 55 °C. High-temperature ground introduces additional thermal energy that accelerates reactions regardless of inhibitor; managing hot and reactive ground is a separate challenge. One of the basis-of-safety assumptions was that ground temperature was in the normal range for the duration of the 90-day sleep time. In mines with hot ground (>55 °C) or where there is evidence of selfheating (even if the temperatures are below 55 °C), the allowable sleep time will still be limited to hours, because further self-heating after loading is likely and even at low rates the effect will be significant over several days. The parallel product development stream of the project resulted in a new bulk emulsion explosive range, called MarathonTM i . This inhibited product was formulated to meet the target of 90-day sleep time in reactive ground, supported by the test protocol reported here. SubtekTM MarathonTM i has been manufactured at production scale and is undergoing field trials at several sites.
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