Fragmentation analysis for underwater ordnance disposal

Abstract

Explosive weapons may cause damage through both blast loading and fragmentation of their casings. Although air-detonated ordnance has been extensively studied, fragmentation hazards from underwater munitions remain underexplored, and therefore no standardised procedure exists to calculate safe standoff distances as a function of depth and charge mass in naval environments. This significantly hampers the safety planning process for underwater explosives ordnance disposal activities. Building on prior laboratory investigations of underwater fragmentation, this study extends the analysis toward full-scale applicability by estimating maximum fragmentation ranges and applying injury-criteria models to assess associated hazard limits. A series of well-controlled small-scale experiments compared cased explosive charges detonated in air and at varying submersion depths. Three casing configurations were tested to quantify the influence of depth and casing configuration type on fragment generation, in-flight behaviour, and size–velocity distributions. High-speed videography and in-situ witness panels were utilised to track fragmentation post-detonation and estimate velocities during flight and after impact. An in-house analysis code with optical and panel data was developed to compute fragment trajectories, maximum ranges, and soft-tissue penetration probabilities using established injury thresholds. Results indicate a pronounced reduction in fragment count, velocity and launch angle with increasing submersion depth, producing substantially shorter predicted penetration distances for all tested submerged charges. This paper outlines a practical methodology for scaling experimental observations toward larger charge masses and discusses implications for risk assessment and mitigation during underwater munitions clearance operations.