1950 laboratory testing for 4 times the planned sleep duration (up to a 28-day test for a 7-day field sleep time) and generally advises one week as the maximum without special precautions. Beyond one week, mines must perform additional risk assessments in collaboration with the explosive supplier, that may include extended lab tests. Sulphide minerals are almost ubiquitous through metal mines (D. Vaughan, 2017), and iron sulphides in particular are commonly co-located-located with coal worldwide (Swaine, 1984). However, reactive ground was identified in about 1 in 5 mines over the course of their operations. The level of reactivity can vary with geology both between sites or even between mining areas at a mine (Valenta, 2019) (M. Frenzel, 2023). Understanding the level of reactivity requires close cooperation with the geology teams to ensure targeted worst-case sampling. There are some mines or mining areas that won’t be suitable for long sleep times, for example if there are self-heating ores that could exceed the safe temperature over time or if the reactive samples fail the qualification test by overwhelming the inhibitor system in the product. New mining methods made possible by wireless blasting demand longer sleep times still. Orica’s analysis of WebGenTM-enabled mine plans identified the need to increase the bulk explosive sleep time up to around 90 days to deliver the full benefits of safety and productivity. Crucially, no standard test protocol or industry precedent existed to qualify explosives for such long sleep times in reactive ground. Two key gaps had to be addressed: (1) developing a reliable laboratory testing methodology to qualify an inhibited explosive to safely withstand ~3 months in reactive conditions, and (2) formulating an explosive with sufficient inhibitor to pass such a test while still meeting operational, cost and performance needs. Before this work, attempts to extend reactive-ground sleep times were limited and ad hoc. By 2020, Orica had introduced an extended sleep time test that qualified certain bulk products for up to 30 days in reactive ground. That approach used layered controls in an extended duration test with a large safety margin, moisture of the sample maintained within a narrow range and additional formulation controls. While it represented a step-change – going from 7-day to 30-day approvals – it was still constrained. Simply prolonging the conventional isothermal test further was considered impractical: for instance, attempting to qualify a 90-day sleep using the same 4× rule would entail a 360-day lab test, which is untenable for timely decision-making. Moreover, long static tests introduce problems like a large burden on testing facilities and changes in the sample matrix which can mask potential reactions. Clearly, a new methodology was needed that could predict long-term stability without having to wait for the full duration in the lab. This paper presents an innovative approach to qualifying explosives for extended sleep times (up to 90 days) in reactive ground, developed under Orica’s MarathonTM i range. The focus is on the reactive ground test program and its outcomes. The paper will detail how a combination of laboratory isothermal tests, Accelerating Rate Calorimetry (ARC), and thermal modelling was used to understand the chemical and thermal interactions possible between AN-based products and Reactive Ground over prolonged periods. A new extrapolation-based test protocol was developed based on the industry standard 28-day isothermal reactive ground test. In parallel, a compatible bulk explosive formulation was designed to meet the 90-day requirement. Together, these advances allow safe long-sleep time charging in reactive ground, unlocking the full value of wireless blasting while maintaining rigorous safety standards. Safety-endorsed hot and reactive ground sleep times have progressed incrementally over decades. summarises the historical evolution of Orica’s reactive ground sleep time limits and test methods, leading up to and including the present work.
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