The sustainment of military training ranges is a major concern for the Department of Defense. Research conducted under several SERDP projects (ER-1155, ER-1481, and ER-2219) found that the greatest and most readily-available sources of energetic compounds on training ranges are low-order (LO) detonations. Comprehensive characterization of residual energetic particles from LO detonations are needed to understand range environmental impacts and to refine fate and transport models that estimate sustainment risks. Until recently, there has been no reliable method of quantifying energetic residues from different detonation scenarios or of realistically simulating a LO detonation. Under SERDP project ER-2219, a method was developed for controlling detonation order using a command detonation system and recovering intact post-detonation explosive particles.

The primary objective of this project was to validate and demonstrate a method of command LO detonation, residue sampling, and laboratory analyses for mortar munitions filled with conventional and insensitive high explosives. The secondary objective was to transfer collected comprehensive data on LO detonation particle characteristics to fate and transport models.

The technology utilizes sampling and analysis techniques developed through multiple SERDP and ESTCP projects. The major techniques demonstrated during this project include: 1) LO detonation sampling and analysis with insensitive and conventional munitions and 2) laser diffraction particle size analysis of post-detonation energetic particles. The ability to conduct LO command detonation testing starts with the Cold Regions Research and Engineering Laboratory fuze simulator (CFS), which consists of a center-drilled aluminum plug with a booster well at the threaded base. The booster well can be loaded with Composition-C4 (C4) explosive to simulate the booster pellet in a normal fuze. The fuze simulator is threaded into the body of an artillery projectile and initiated using a standard military blasting cap. The field-adjustable C4 booster is what drives the versatility of this system and allows it to be used for both high-order command detonations as well as LO detonations demonstrated here. The particles released from LO detonations can then be recovered when tests are conducted on ice. Ice provides an ideal testing surface because it isolates the test area from previous activities and allows for both large (>1 cm) and small (1 cm – 10 nm) post-detonation particles to be clearly visible for cataloguing by distance from the point of detonation. The smooth surface of the ice allows for incremental distance areas to be swept clean, ensuring that the majority of material ejected is recovered for characterization. These particles can then be isolated from any incorporated snow and ice by freeze drying in the lab. Following laboratory isolation, the particles can then be characterized by Laser Diffraction Particle Size Analysis, morphology by Scanning Electron Microscope and Micro Computed Tomography, and particle compositional analyses by High Performance Liquid Chromatography.

Critical Findings

The following critical findings were developed:

• The methodology provides realistic energetic particle characteristics for size, distribution, chemical composition, and morphology to fate and transport models, rather than assuming inputs.
• Energetic purity analysis and scaling can assess potential preferential consumption and/or deposition of energetics.
• Data from Laser Diffraction Particle Size Analysis (LD-PSA) is more highly resolved than previous sieve stack methods.
• The methodology is best suited for munitions nearing approval or already approved for use on training ranges.
• LD-PSA was validated for use on both insensitive and conventional energetic particles with estimation of refractive indices and successful replicate runs.
• LD-PSA agreed well with sieve-stack analysis through comparing cumulative volume and mass percent, respectively, and provided a more highly resolved dataset.
• Testing and sampling on a frozen ice surface provides best setup for particle sampling.
• Dedicated testing space with ice maintenance in between testing events is ideal.
• Fuze simulator or modification of standard issue fuze is required to achieve consistent consumption outcomes.

The main issues when implementing LO command detonation testing and sampling are the ability to consistently achieve LO detonation functioning, as currently defined, and building/maintaining a suitable testing site. More precise bounds on variability of LO detonation particle characteristics within a given munition would require an increased number of replicate detonations and accompanying increased numbers of samples and analyses. Implementation of this technology would be considered successful if it were to be adopted into use when performing a Life Cycle Environmental Assessment (LCEA) of a new munition. Following this, subject matter experts in the fate and transport of energetic materials within the environment could utilize the data from the LCEA to better refine their models and therefore predictions of relative impact of LO detonations. (Project Completion - 2022)