Defence Research and Recherche et développement Development Canada pour la défense Canada Assessment of Lower Leg Injury from Land Mine Blast – Phase 1 Test Results using a Frangible Surrogate Leg with Assorted Protective Footwear and Comparison with Cadaver Test Data D.M. Bergeron, G.G. Coley, R.W. Fall Defence R&D Canada – Suffield I.B. Anderson Canadian Forces Medical Group Technical Report DRDC Suffield TR 2006-051 February 2006 Assessment of Lower Leg Injury from Land Mine Blast – Phase 1 Test Results using a Frangible Surrogate Leg with Assorted Protective Footwear and Comparison with Cadaver Test Data D.M. Bergeron, G.G. Coley, R.W. Fall Defence R&D Canada – Suffield I.B. Anderson Canadian Forces Medical Group Defence R&D Canada – Suffield Technical Report DRDC Suffield TR 2006-051 February 2006 Author D.M. Bergeron Approved by Dr. Chris A. Weickert Director, Canadian Centre for Mine Action Technologies Approved for release by Dr. Paul D’Agostino Chair, Document Review Panel © Her Majesty the Queen as represented by the Minister of National Defence, 2006 © Sa majesté la reine, représentée par le ministre de la Défense nationale, 2006 Abstract In 1999, the Canadian Centre for Mine Action Technologies (CCMAT) sponsored a series of tests involving the detonation of 25 anti-personnel blast mines against a frangible leg model. The model was fitted with various footwear and additional protective equipment. The aim of these tests was to assess whether this model could be used for routine tests of protective footwear against mine blast. The report describes the frangible leg and compares it to its human counterpart. It then presents an overview of the physics of mine blast and the devastating effects on the human leg. Details of the test setup and procedures are described so that the reader might better interpret the test results. These tests involved medical staff, including two surgeons that had operated on mine blast victims, to examine the frangible legs and determine probable medical outcomes. These results are compared to a database of mine blast injury against human cadavers to identify the strengths and limitations of the frangible leg model. It was found that this frangible leg model has potential to be a good testing tool, provided some modifications are implemented, and further testing be carried out to properly calibrate the response of the modified model against the database of mine injuries. DRDC Suffield TR-2006-051 i Résumé En 1999, le Centre canadien des technologies de déminage (CCTD) commanditait une série d’essais impliquant la détonation de 25 mines terrestres anti-personnelles contre des jambes synthétiques. Chaque jambe était chaussée d’une botte régulière ou anti- mine, parfois avec un équipement de protection supplémentaire. Le but de ces essais était de déterminer si cette jambe synthétique peut devenir un outil courant pour évaluer la performance de bottes anti-mines. Ce rapport décrit la jambe synthétique et la compare à son homologue humain. Le rapport présente ensuite un survol de la physique des explosions de mines terrestres à effet de souffle et leur effet dévastateur sur la jambe humaine. Les détails concernant la préparation et la conduite des essais est décrite pour que le lecteur puisse mieux interpréter les résultats ci-joint. Une fois les essais conclus, du personnel médical, y compris deux chirurgiens ayant déjà opéré sur des pieds de mine, ont examiné les jambes synthétiques afin de déterminer ce qui serait arrivé à un être humain. Le rapport compare ces résultats à une base de données établie lors d’essais qui opposaient des cadavres humains contre des mines terrestres. Cette comparaison a permis d’établir que cette jambe synthétique peut devenir un bon outil pour ce genre d’essais moyennant qu’un nombre d’améliorations y soient apportées et qu’une nouvelle série d’essais soit faite pour calibrer la réponse de la jambe améliorée contre la base de données susmentionnée. ii DRDC Suffield TR-2006-051 Executive summary In April 1999, the United States Humanitarian Demining Program sponsored the Lower Extremity Assessment Program (LEAP). The purpose of LEAP was to assess the effect of a land mine explosion on the human foot as a function of protective footwear. These tests were particularly useful because human cadavers were used to provide detailed information about injuries to soft tissues and bones. However, only authorized institutions can perform such tests and biomedical expertise is required to fully realise the benefits. It also involves special handling considerations because dead human tissues pose a biohazard. Another consideration is that the age, sex and body- build of the subjects can vary widely, which might introduce a large variance in bone strength and body dimensions. Industry and test agencies find it difficult to use cadaver models for routine tests when developing mine-protected footwear. Recognising this fact, the Canadian Centre for Mine Action Technologies (CCMAT) sponsored twenty-five tests in September 1999 to assess the Australian Frangible Surrogate Leg (FSL) for its use as a tool for this niche market. Pending positive results, CCMAT proposed to develop suitable injury criteria for the FSL. The main objective of the CCMAT tests was to assess the feasibility of the FSL as a test model and develop mine blast injury criteria so it might be used in routine blast tests of protective footwear. The development of injury criteria would be achieved by comparing the results with those from the LEAP tests. To make this comparison, it was necessary to perform the CCMAT tests in the same way that the LEAP tests were performed, which involved reproducing as many test parameters as possible, such as the selection and placement of the mines, the soil type, the footwear, etc. In addition to the primary objective, the CCMAT tests also assessed the repeatability of the FSL as a diagnostic tool; acquired physical data using strain gauges and a load cell to determine their potential as instrumentation for the FSL; evaluated the relative protective performance of a small selection of footwear; and obtained structural response data for mines with an explosive mass between those of the M14 (29grams) and PMA-2 (100grams), which were used during LEAP. This test series partially achieved its primary objective: it demonstrated that the FSL has the main attributes required from a model for routine mine blast tests of protective footwear. The test results indicate that the FSL can reproduce the same result, within reason, when it is subjected to the same explosive stimulus. It is also capable of producing different results when the explosive stimulus or the level of protection is changed. The other part of the primary objective—to correlate the response of the FSL to human injury from anti-personnel land mines—could not be achieved because of differences in test conditions between the FSL and LEAP tests. The most important difference was that M14 mines could not be obtained in time. The PMA-3 mine used as a substitute is more powerful than the M14, which meant that one-to-one DRDC Suffield TR-2006-051 iii comparisons could not be made with confidence in the regime where protective footwear can make a difference. The flash x-ray images captured during these tests provide much insight into the injury mechanisms for mine blast trauma. These images show the existence of a hemispherical zone of high-pressure gas that imparts localized damage to those parts of the footwear in the immediate vicinity of the mine. There exists a small zone directly above the mine where the vertical push from the gas is particularly focussed, as evidenced by the deformation shape of the blast deflector embedded in the sole of the Wellco® blast boot. When a blast boot is used in conjunction with an additional protective overboot, this zone of focussed momentum transfers significant loading through the lower deflector to the upper deflector. This has implications for the design of protective footwear. It suggests that the inclusion of any solid object in the sole of the boot must be done with care. The blast imparts momentum to such an object, which can become a projectile capable of penetrating the plantar region of the foot, as was the case for the steel shank in the sole of the standard combat boot of the Canadian Army. The flash x-ray images also demonstrate that the force of the impact can be so severe that the closer bones, particularly the calcaneus, are pulverized. Furthermore, it is clear that the damage to the leg starts distally and travels up, remaining relatively localized. When using a boot in isolation, even a mine-protected boot, the smallest mine destroyed the footwear. Adding further protective equipment affected the outcome of the tests. It appears that the additional protective footwear plays a sacrificial role to divert some of the force of the explosion while distancing the inner footwear from the zone of very high-pressure close to the mine. For the PMA-3, the overboot prevented total destruction of the inner footwear, but momentum transfer to the blast deflector of the overboot, particularly to the portion located directly above the mine, was large enough to deform the blast deflector located above in the sole of the inner boot. The arch of the boot was increased permanently. As the explosive content of the threat increased, the arch deformed further and tears began to appear in the upper and rear vamp of the inner boot. For the PMA-2 mine, the force transfer from the explosion was so strong that the foot of the FSL burst, ripping the boot open in the process. The increased standoff of the Spider Boot® combined with displacement of the detonation point outside the footprint produced the best protection results during this test series.