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3 Thermobaric Explosives CURRENT FOCUS Of the topics assigned to the committee to review, only the area known as thermobarics has received national attention in the open media and throughout the DoD/DOE/Defense Threat Reduction Agency (DTRA) community. The committee heard extensive presentations by speakers from Sandia National Laboratories (SNL), Lawrence Livermore National Laboratory, agencies from the United Kingdom and Canada, and DoD agencies.- While the focus of these groups varies significantly, each of the presentations began with reference to weapons of the former Soviet Union (FSUy, fielded in the 1980s, that were deployed by the FSU in Chechnya and which reportedly exhibited highly unusual effects in confined environments. The interest in these reported effects has grown exponentially. BACKGROUND AND CURRENT RESEARCH The Russian military uses the term "thermobaric" to describe a class of munitions that the FSU investigated beginning in the 1960s; fielded FSU systems of this type appeared in the 1980s. This new class of energetic material, closely related to metallized fuel-air explosives, has received extensive attention in recent months. Indeed, the use of a "thermobaric" weapon by the U.S. military in Afghanistan was widely reported by the news media. The extensive reporting surrounding these events has led to a lack of specificity in the use of the term "thermobaric." Early reports claimed that these energetic materials provide vastly increased performance relative to conventional high explosives. These claims appear to be based on anecdotal evidence from selected tests rather than on scientifically rigorous data. 3 R.J. Bartlett, Universityof Florida. 2002. Presentation to the committee. April 18. M. Baer, SNL. 2001. Presentation to the committee. December 13. J. Walton, CIA. 2001. Presentation to the committee. December 13. 4 A. Kuhl, LLNL. 2001. Presentation to the committee. October 25. 5 K. Kim, DTRA. 2001. Presentationto the committee. December 13. 6 A. Kesby, UK DERA. 2001. Presentation to the committee. December 13. 16
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THERMOBARIC EXPLOSIVES 17 While the Russian military identifies its weapons systems as thermobarics, the Russian scientific community refers to these materials as low-density explosives, or metallized volumetric explosives. Studies of thermobaric systems in the West date to about 1988 and were driven primarily by interest from the intelligence communities and by efforts to exploit foreign technology. A working definition of the term evolved, defining the thermobaric weapon as a single-cycle, fuel-rich explosive system that has a long-duration thermal pulse accompanying and supporting shock output. The term "thermobaric" now appears to be synonymous with fuel-rich or enhanced-blast explosives. Current thermobaric munitions have been purported to exploit secondary combustion as a source of lethal energy and as effectively providing increased internal blast energy when deployed against soft targets such as buildings and against personnel and equipment inside confined targets, including tunnels and caves. Whether or not the extra combustion energy enhances the lethality of a munition depends on how the extra energy couples with the target. Energy that does not contribute to the detonation (shock) regime may still prove lethal if it can add to the total impulse within 10s of milliseconds inside a building or up to a second within a tunnel.7 Further, the addition of materials that increase the density of the fireball may improve the coupling between it and the target, which can provide additional effectiveness. While extensive modeling studies are currently under way, few if any of these phenomena are well understood in the context of a thermobaric explosive application. Careful trade-off studies that examine the contributions of these effects are necessary for their successful implementation. The committee's assessment of the present state of thermobarics research and testing in the United States is that it is relatively immature and not particularly well structured.s As discussed further below, the committee believes that this is a result of the following: The speed with which the United States attempted to field a thermobaric munition clone for use in Afghanistan; The inability and reluctance of the services to field new materials (hence, the redefinition of thermobarics to include Indian Head Explosive 135 fIH-13511; · The unclear definition of terms; The lack of careful analysis and experimentation; Inadequate diagnostics that have perpetuated the reliance on anecdotal evidence as opposed to data; and Testing against varied types of targets and unclear scale effects. An advanced concept technology demonstration (ACTD) effort was initiated by the Defense Threat Reduction Agency in 2001. It was to be a 3-year program. Driven by media reports from Chechnya and in the aftermath of September 11, 2001, the DoD and DTRA diverged from the original plan and embarked on an ambitious, 60-day ACTD program to demonstrate a thermobaric weapon in Afghanistan. The materials studied were conventional high explosives that included some of the features seen in Russian thermobaric systems, which utilized fuel-rich, heavily metallized, minimally confined explosive fills. In contrast to the recent U.S. effort, much of the work done on thermobarics by others outside the United States focused on direct experimentation, some of which was quite sophisticated and dealt directly, although empirically, with the difficulty in measuring the performance of particular explosive devices. In the aforementioned presentations to the committee, evidence showed that the performance of this type of thermobaric explosive is 7 H. Shechter, OSU. 2001. Synthesis of 1,2,3,4-Tetrazines Di-N-Oxides, Pentazole Derivatives, and Pentazine Poly-N-Oxides. Presentation to the committee. December 13. K. Kim, DTRA. 2001. Presentation to the committee. July 31.
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18 ADVANCED ENERGETIC MATERIALS highly dependent on test configuration. This raises a serious question regarding the battlefield effectiveness outside of a very specific target set; fortunate placement of a weapon may even be required in order to achieve the expected effect. TRANSITION BARRIERS The impetus to field a thermobaric weapons system has been understandable in light of reports from Afghanistan where the military target mix included some targets that were vulnerable to enhanced blast and increased impulse. However, the committee believes that the accelerated efforts to develop fieldable systems are counterproductive. In particular, the ACTD that led to the BLU-118B expended considerable resources while fielding a munition of, at best, only marginal improvement over its predecessor. The munition's configuration (a heavily confined warhead body) and the material (IH-135) appear to have been selected on the basis of programmatic expediency rather than thoughtful optimization. Only a longer and broader view will avoid certain disappointment with limited progress in this potentially promising technology area. The Advanced Energetics Initiative has funded work focused on understanding the fundamental physical phenomena of thermobaric explosives. This project is focused on the underpinning physics of thermobaric systems, including studies of detonics, material dispersal, turbulence, pressure- and temperature- dependent ignition of metal combustion, energy release, couplingto targets, and comparison with traditional devices. The work will give priority to understanding known thermobaric systems, even if they are not optimized for deployment by the services. High-fidelity diagnostics development is critical to the success of this effort. Field tests could supplement scientific laboratory-scale experiments. Proposed model development and model validation are a necessity for predictive understanding of thermobaric explosive systems. FlNDiNGS AND RECOMMENDATIONS Findings The committee found the following with regard to current work in the field of thermobaric explosives: · The implementation of thermobarics may offer the first major shift in explosives application since the introduction of the shaped charge. If the underlying principles can be understood and consistently controlled, a significant new weapons system or series of weapons systems may become available to the warfighter. The engagement of formulators early in the development and characterization of potential thermobaric explosive formulations is necessary in order to capitalize on their experience and insight into advantageous material properties. A wealth of experience related to the Fuel-Air Explosives (FAE) programs exists in the services to assist in material selections and possible formulation guides. As with all explosive materials, chemical composition is only a starting point in discussing performance. Many safety and performance properties are related to purity, particle morphology, material density, binder selection, and processing methods. Parametric studies of specific formulations will be needed to characterize the structure and optimize the performance of thermobaric systems. Work on the predictive tools, test methods. and carefully crafted parametric studies on potential formulations is currently making good progress, and further success will ensure an effective and efficient program to weaponize a thermobaric explosive. .
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THERMOBARIC EXPLOSIVES 19 Recommendations In order to further develop thermobaric weapons systems the committee recommends the following: . · An evaluation and ranking of candidate thermobaric materials should be undertaken. The explosives community typically ranks explosive materials by some figure of merit, typically detonation velocity or pressure. Through decades of scientific study, such detonation properties have been used to predict performance characteristics such as brisance (the rapidity with which an explosive develops its maximum pressure). The TNT-equivalence for blast overpressure has also been used to rank explosives. Because thermobaric materials may not detonate efficiently and their lethal effects may include temperature and impulse, traditional detonation properties and TNT-equivalence are unlikely to provide the necessary figures of merit. A simple, direct measurement tool is needed. One such tool is the "stop sign" reported by Canadian researchers.9 A concerted and focused effort is needed for understanding the phenomenology of enhanced-blast kill mechanisms and what they may offer over conventional munitions in effectiveness. This effort should be conducted to the point at which the major parameters influencing enhanced-blast effectiveness have been identified and incorporated into a model useful for effectiveness calculations and design of weapons. · Warhead designs should be based on sufficient understanding of mechanisms in order to guide design toward optimal performance. 9 D. Frost, McGill University. 2001. Presentation to the committee. April 29.
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