Characterizing the initiation capacity of low-density granular explosives

Abstract. In the context of an improvised explosive threat, certain "dual use" substances are of particular concern. According to international storage and transportation standards, these substances are not considered explosives because they are too insensitive [1]. While this approach is relevant to transportation and storage safety, it does not address the potential misuse of these substances. Some substances, typically classified as oxidizers, could therefore be misused in explosive devices. One well-known example is the adduct of urea and hydrogen peroxide (UHP) [2-6]. The threat level of these substances is assessed based on their critical diameter and the type of booster required. The threat level is significantly higher if these substances can be detonated with a booster made of homemade explosives, such as TATP (triacetone triperoxide). Such substances are often encountered in granular explosives with low densities, typically below 1 g/cm³. Thus, threat assessments of "dual-use" explosive substances require descriptions of the initiation capabilities of homemade granular explosives. Current detonation research focuses heavily on high-density military explosives. In contrast, low-density granular explosives (typically <1 g/cm³) are poorly understood. Existing literature often focuses on their blast wave effects rather than their ability to act as boosters for secondary main charges [7-8]. This study establishes experimental methodologies to characterize the initiation capacity of these materials. Using advanced diagnostics, including photonic Doppler velocimetry (PDV), streak cameras, and witness plate indentation, we compare various granular explosives of different particle sizes and densities against a high-density military reference. The experiments revealed that some low-density granular charges exhibit behavior related to their granular nature that may be associated with particle jetting and granular bed compaction. These findings provide new insights into the detonation mechanisms and initiation capabilities of granular substances. [1]United Nations Economic Commission of Europe, Classification procedures, test methods and criteria relating to explosives of class (Test methods and criteria 2023). [2]A. K. Hussein et al., Chin. J. Explos. Propellants 2016, 39, 22-27. [3]R. Matyas et al., Propellants Explos. Pyrotech. 2017, 42, 198-203. [4]F. Halleux et al., Propellants Explos. Pyrotech. 2022, 47, e202100250. [5]F. Halleux et al., Propellants Explos. Pyrotech. 2023, 48, e202300011. [6]F. Halleux et al., Propellants Explos. Pyrotech. 2023, 48, e202300116. [7]S. Zeman et al., J. Hazardous Mater. 2008, 154, 192-198. [8]J. Pachman et al., Shock Waves 2014, 24, 439-445.