8

Medical Basis for Future Body Armor Testing

This chapter discusses thoracic ballistic test methodologies, blast injury criteria and blastlike mechanisms, injury scales, potential adverse effects of body armor in blast exposures, possible injury to body organs remote from blunt trauma, and instrumented simulators for research.

THORACIC BALLISTIC TEST METHODOLOGIES

As discussed in Chapter 3, modern body armor can defeat incoming pistol and rifle rounds, trading energy and momentum of the round for deformation of the armor. This deformation, however, has the potential for creating injuries in the thorax behind the armor, as well as injuries to remote organs, that may generally be characterized as blunt trauma.

Introduction to Behind Armor Blunt Trauma

Injuries to the thorax due to deformations of the armor are often termed behind- armor blunt trauma (BABT). Backface deformation (BFD) of the armor can cause local and distant fractures, contusions and hemorrhage in the thorax, as has been demonstrated in numerous animal studies (e.g., Prather et al., 1977; Clare et al., 1975; Cooper et al. 1982; Suneson et al., 1987; Lidén et al., 1988; Knudsen and Gøtze, 1997; Sarron et al., 2000; Gryth et al., 2007; Mayorga, 2010). These injuries are the result of physical deformation of the back face of the armor and associated stress waves that propagate through the thorax. While BABT is a known phenomenon, what is not known is the extent to which there may be significant injury to organs more distant from the point of impact, such as the brain, heart, spinal cord, and gut due to significant pressure waves transmitted through the body armor that result in pressure waves or shear waves in the body.

The injury risk for BABT will generally depend on the type and configuration of armor, the round, and the delivered energy of the round that results in an impact displacement and profile. This impact displacement and profile also depend on the physical characteristics of the person wearing the body armor. For both the body armor and the thorax, the impact location is important, and for the thorax, the rate sensitivity of the impact may be large. Many comprehensive discussions of penetrating ballistic trauma exist (e.g., Ryan et al., 1997), but there are relatively few such discussions on the topic of nonpenetrating



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PREPUBLICATION DRAFT—SUBJECT TO EDITORIAL CORRECTION 8 Medical Basis for Future Body Armor Testing This chapter discusses thoracic ballistic test methodologies, blast injury criteria and blastlike mechanisms, injury scales, potential adverse effects of body armor in blast exposures, possible injury to body organs remote from blunt trauma, and instrumented simulators for research. THORACIC BALLISTIC TEST METHODOLOGIES As discussed in Chapter 3, modern body armor can defeat incoming pistol and rifle rounds, trading energy and momentum of the round for deformation of the armor. This deformation, however, has the potential for creating injuries in the thorax behind the armor, as well as injuries to remote organs, that may generally be characterized as blunt trauma. Introduction to Behind Armor Blunt Trauma Injuries to the thorax due to deformations of the armor are often termed behind- armor blunt trauma (BABT). Backface deformation (BFD) of the armor can cause local and distant fractures, contusions and hemorrhage in the thorax, as has been demonstrated in numerous animal studies (e.g., Prather et al., 1977; Clare et al., 1975; Cooper et al. 1982; Suneson et al., 1987; Lidén et al., 1988; Knudsen and Gøtze, 1997; Sarron et al., 2000; Gryth et al., 2007; Mayorga, 2010). These injuries are the result of physical deformation of the back face of the armor and associated stress waves that propagate through the thorax. While BABT is a known phenomenon, what is not known is the extent to which there may be significant injury to organs more distant from the point of impact, such as the brain, heart, spinal cord, and gut due to significant pressure waves transmitted through the body armor that result in pressure waves or shear waves in the body. The injury risk for BABT will generally depend on the type and configuration of armor, the round, and the delivered energy of the round that results in an impact displacement and profile. This impact displacement and profile also depend on the physical characteristics of the person wearing the body armor. For both the body armor and the thorax, the impact location is important, and for the thorax, the rate sensitivity of the impact may be large. Many comprehensive discussions of penetrating ballistic trauma exist (e.g., Ryan et al., 1997), but there are relatively few such discussions on the topic of nonpenetrating -169-

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PREPUBLICATION DRAFT—SUBJECT TO EDITORIAL CORRECTION ballistic trauma, especially those that might be relevant to injuries associated with bullets and shrapnel striking body armor. This section presents the physics, biophysics, and methods of studying nonpenetrating blunt trauma with the goal of optimizing the design and testing of manufactured body armor. A bullet is a localized source of energy that can cause high local compression and shear forces, penetrating protective layers. The most effective bullets deposit energy, shear, and momentum rapidly in the target. One general strategy for protection is to blunt the penetration of the incoming round, picking up as much mass as possible in the body armor while decreasing the round energy and increasing the contact area. Thus, the protective effect of any ballistic protective vest is provided by increasing the area of impact, thus transferring energy and momentum to the vest. However, effective transfer of large amounts of energy and momentum from the incoming round into the body armor generally implies some deformation of the rear, or back face, of the body armor. The BABT deformation is generally larger under soft body armor for a given incoming round. An interesting comparison of energy and momentum scales may be seen by comparing characteristics of various rounds, as shown in Table 8-1. Energy varies by a factor of over 30 between the relatively slow 9 mm handgun round and the .50 caliber (12.7 mm) rifle round due to the differences in mass and velocity. TABLE 8-1 Muzzle Parameters for Various Types of Rounds Device Muzzle Round Energy (kJ) Momentum Velocity (m/sec) Mass (g) (kg m/sec) 9 mm 358 8 0.5 2.86 5.56 × 45 M193 ball 991 3.6 1.7 3.57 7.62 × 51 NATO ball 838 9.6 3.4 8.13 12.7 mm 50 M2 890 42 16.6 37.4 SOURCE: Ness, 2011. A further elucidative comparison may be made between the impact energy and momentum scales of low-rate blunt trauma events such as automobile impacts and high- rate impact events such as BABT. The energy and momentum for various potential blunt trauma situations are shown in Table 8-2 and are plotted in Figure 8-1. It is apparent from Figure 8-1 that a nonpenetrating ballistic impact involves much lower total momentum transfer than typical low-rate blunt impacts. However, the energy transfer is comparable, depending on the round and impact velocity. This implies increased localization of energy transfer and shorter interaction time and likely increased localization of injury. -170-

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PREPUBLICATION DRAFT—SUBJECT TO EDITORIAL CORRECTION TABLE 8-2 Energy/Momentum for Various Typical Thoracic Trauma Situations Action Velocity Mass Energy (kJ) Momentum (m/sec) (g) (kg m/sec) U.S. Football Block 5 100,000 2.5 500 5 50,000 0.6 250 Automobile Thoracic Dash Impact Automobile Head Impact 5 5,000 0.06 25 a Blast ~300 ~ 0.0004 0.0013 0.00001b 6.7 x 10-6 Ultrasound Damage ~1,500 ~ a Based on assumed total lung volume of 3,000 mL. b Based on applied lung volume of 300 mL. SOURCE: Cameron Bass, Duke University FIGURE 8-1 Initial energy and momentum for ballistics and other blunt impacts. SOURCE: Bass, unpublished. -171-

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PREPUBLICATION DRAFT—SUBJECT TO EDITORIAL CORRECTION Blast injury can occur with very small impact momentum and energy over very short time scales. In the limit, as the duration of such impacts becomes very short, an interesting comparison may be made with damage using ultrasonic energy. At high rate (~4 MHz), less than 20 cycles of acoustic energy delivered to lung tissue with a peak pressure of approximately 1 megapascal (MPa) will cause tissue damage (see Raeman, 1996). It is uncertain if these high frequency effects occur with BABT. Figure 8-2 shows a high speed X-ray of deformation of hard body armor after rifle round impact. The chest deformation shown here may lead to trauma to ribs, lungs, heart, liver, and other organs. Data are needed to determine the optimum vest design that provides protection to the body, potentially including organs remote from the site of impact while minimizing weight that the soldier must carry. FIGURE 8-2 Superimposed high-speed X-rays of the initial shock wave and deformation of the thorax during a 7.62 mm projectile live-fire test in a pig protected by hard body armor. SOURCE: Mayorga et al., 2010. This section summarizes and evaluates the current body of evidence for behind- armor effects and whether the current standards for body armor provide sufficient protection to soldiers and law enforcement personnel. As will be seen, attempts to document the effects in animal models have been impaired owing to the inadequate numbers of test subjects studied and inadequacies in test design (e.g., incomplete pressure sampling, instrumentation deficiencies, limited measurement methods, short duration of follow-up). Much is still unknown about the injury mechanisms of BABT. The information provided can be used so that more informed recommendations can be made about the types of further studies needed, such as studies in large animals, physical models, and computer-based -172-

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PREPUBLICATION DRAFT—SUBJECT TO EDITORIAL CORRECTION simulations. It is important to conduct experiments to define the thresholds of energy transfer and the biophysical mechanisms that produce significant injury, as well as to evaluate if and how body armor can be improved to prevent remote injury and/or incapacitation. Ergonomics of Body Armor Until the eighteenth century, combat infantry soldiers are estimated to have carried 15-30 kg (33-66 lb), with the remaining equipment and supplies being transported in a baggage train (Knapik et al., 1996). The weight burden in recent times has increased substantially. Negative consequences of substantial load carriage include potential heat stress (Barwood et al., 2009), decrements in psychomotor performance (Bensel, 1975), and ergonomic factors that may limit mobility (e.g., Harman et al., 1999). Beekley (2007) found also that significant increases in oxygen consumption, respiration, and heart rate for loads to 70 percent of lean body mass in male U.S. Army personnel. Current body armor basic system mass is 7.1 kg (15.7 lb), accounting for 15 percent of typical maximum load carriage, but can be as high as 15.1 kg (33.3 lb), or 31 percent of maximum load carriage. Clearly, reductions in body armor mass are a potential method of reducing total load carriage and increasing mobility on the battlefield. Finding: Carried mass, such as that associated with body armor, may decrease a soldier’s mobility and lead to fatigue. Additional studies of the relationships between injury and the energy and momentum transferred to a body protected by armor innovations could lead to lighter weight armor that provides survivability equivalent to that of current military issue. However, the potential benefits of reducing the load carriage of body armor must be carefully weighed against the advantages of enhanced deformation that may arise from reduced areal density. The U.S. government and the North Atlantic Treaty Organization (NATO) are currently pursuing these goals.58 Injury Biomechanics Beyond the development of techniques to identify injuries from BABT, it is important to develop a technique for assessing the risk of injury to humans behind body armor. One technique that has been shown to be effective in many fields of injury biomechanics is the use of an instrumented surrogate (dummy) to 58 See, for example, the U.S. Army Research Institute of Environmental Medicine (USARIEM). Available online at www.usariem.army.mil/pages/download/LoadCarriagePDF.pdf and http://www.nwguardian.com/2010/12/09/9152/jblm-soldiers-provide-feedback.html. -173-

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PREPUBLICATION DRAFT—SUBJECT TO EDITORIAL CORRECTION evaluate the risk of injury from blunt trauma in automobile crashes. Elements of this technique include the following:  Biofidelic surrogate. A dummy that is robust, gives a repeatable physical response, and responds in a human manner. A dummy may be physically very simple and may represent only a part of a human body. For example, an instrumented beam has been used successfully to represent an arm (Bass et al., 1997), and clay is currently used to represent the human thorax (Prather et al., 1977). However, dummies might be very complex, such as the anthropomorphically correct dummies being developed for the automobile industry. Generally, a surrogate should be as simple as possible while still representing the relevant human response.  Engineering measurement. A physical parameter such as force or acceleration may be used to quantify the physical response of the dummy. Dummies may be instrumented to produce accepted or proposed injury criteria.  Injury risk evaluation. A correlation between an engineering measurement and some injury model. For example, in frontal thoracic blunt impacts, an injury threshold of 60 times the force of gravity is used in the automobile industry.  Validation by injury model. The injury risk evaluation is correlated to a physical model of injury. An injury risk model is without value if it has not been successfully validated using (1) epidemiology or physical reconstruction of an actual injury event, (2) an animal injury model, or (3) a human cadaveric injury model, as shown in Figure 8-3. Development of a relationship between a robust surrogate for injury and a validated injury model is crucial to the success of this approach. -174-

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PREPUBLICATION DRAFT—SUBJECT TO EDITORIAL CORRECTION FIGURE 8-3 Development of surrogate injury model. SOURCE: Bass, 2000. Reprinted with permission of the Center for International Stabilization and Recovery. As discussed above, there are only three ways of obtaining direct injury data. Each technique has its strengths and weaknesses as follows:  Cadaver experiments. A human cadaveric specimen is substituted for a living human body and tested in a realistic manner. The strong advantage of cadaveric experimentation is that the anatomy closely matches that of a living human. Both skeletal injury and tissue damage may be assessed using a cadaveric model. In addition, body kinematics and kinetics may be accurately determined. The principal weakness of cadaveric models is the lack of human physiology. It is not possible to assess certain injuries (e.g. commotio cordis,59 adult respiratory distress syndrome (ARDS), or diffuse axonal injury) using cadavers, as these pathologies require life processes to develop, and some pathological manifestations do not appear until weeks or years after the trauma. 59 Commotio cordis is a disruption of heart rhythm that occurs as a result of a blow to the area directly over the heart at a critical time during the cycle of a heart beat. It frequently results in sudden death. -175-

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PREPUBLICATION DRAFT—SUBJECT TO EDITORIAL CORRECTION  Animal experiments. A living animal is substituted for a living human and tested in a realistic manner. The strong advantage of animal experimentation is that living physiology is available. Thus, animal experimentation can be used to assess injuries that require life processes before they manifest. The principal weakness of animal models is the limited correspondence of animal anatomy with human anatomy. Typical models in current use include porcine, caprine, and bovine models. As livestock is typically quadrupedal, there are substantial differences in cranial and thoracic anatomy between the experimental model and humans. Ethical considerations may present practical difficulties in testing with animals. Often protocols are restricted to following animals for a short period of time (e.g., 2 hr). This may significantly limit the usefulness of animal experimentation for certain types of injuries. As an example, ARDS from traumatic insult requires multiple hours or days to develop. When justified, however, it is ethically permissible to investigate the course of injuries for extended times. The types of experimentation needed are outlined in Appendix J.  Human epidemiology. Observations from injuries suffered by humans in field situations similar to those for which testing is desired comprise the data of epidemiology. The advantage of epidemiology is that it often applies directly to the injury being investigated. For instance, epidemiologic data on injuries and conditions from automobile crashes are collected by the U.S. Department of Transportation for all fatalities and large numbers of nonfatal injuries each year. These data may be used to develop injury models and to focus the development of countermeasures. There are several limitations with epidemiological data. First, there is often limited information on the circumstances under which the injury occurred since the injuries do not occur in a controlled laboratory environment. Second, the data are always retrospective. Epidemiology does not have information on future systems or systems that are not in use. Third, in military environments, the collection of data may be quite difficult, and the information may be sensitive. Volunteer models may not generally be used to obtain injury data (Figure 8-4); ethically, researchers must keep impacts in volunteer experiments below injury thresholds. -176-

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PREPUBLICATION DRAFT—SUBJECT TO EDITORIAL CORRECTION FIGURE 8-4 Volunteer experimentation. SOURCE: Stapp, 1949. The most effective models use as many of these three means of obtaining injury data as possible or as are available for a given injury situation. The models must be appropriately biofidelic (lifelike). In other words, the models must adequately represent a human body in the situation analyzed. It is useful to employ several models (e.g., cadavers and animals) using consistent instrumentation and test conditions. Given appropriate injury modeling, the injury risk might be found to be as realistic as possible; otherwise, there is a potential for increasing the injury risk with inappropriate modeling. Injury Criteria and Experimentation There are a number of potential sources of injury from BABT; these include the initial contact shock, the subsequent displacement of the thoracic wall, and, in some cases, the propagation of pressure. The initial shock may occur with substantial high- frequency components and a relatively low resulting displacement. This shock pressure peak occurs because of the transmission of a pressure impulse from the rear of the body armor into the thoracic wall. Later bulk displacement may occur following significant local momentum transfer between the back of the body armor and the body. There has been extensive investigation into the relative effect of the initial shock and resulting displacements. Animal experiments at Oksbøl, discussed below, were designed to investigate this (Sarron, 2000). This issue, however, has not been completely resolved. Pressure profiles have been measured in tissue simulants for impacts behind body armor. Pressure data from measurements in gelatin simulant material behind 6.4 mm ceramic (24 kg/m2) with aramid composite (10 kg/m2) and a fragment protective vest show an initial pressure pulse of 7.5 MPa less than 0.05 msec wide followed by a second pulse 0.8 msec later (van Bree, 2000). Stress wave propagation and concentration of reflected and refracted waves may -177-

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PREPUBLICATION DRAFT—SUBJECT TO EDITORIAL CORRECTION enhance injury (Lui et al., 1996). This is discussed further in the Oksbøl animal section. The experimental basis for high-rate impact is not well established. Variables that might significantly affect injury potential include delivered energy, thoracic wall displacement, contact area or contact profile, loading rate, and location of impact. It is clear that the more localized the energy, the greater the potential deformation into and through the body armor. Large local displacements may cause destructive local shearing or compression of tissue. Distributed thoracic loading has a different injury pattern than localized loading (Crandall, 1998). Indeed, relatively sharp indent profiles may be assumed by penetrations behind soft body armor (Lewis, 2001) or behind full penetrations of ceramic armor captured in the soft backing material (DeMaio, 2001). The sensitivity of human tissue response to the applied loading rate may be large, and the location of impact is important (e.g., anterior thorax versus lateral thorax). Additional factors may include gender, age, body mass, stature, and other anthropometric parameters. Experimental programs designed to develop standard injury test methodologies usually focus first on a single relevant subject population. This may imply a focus on mid-sized males as being appropriate for a military population. However, it is perhaps necessary to consider gender-related size differences for general applications. In the next section, injury mechanisms and mechanical correlates with injury are discussed. These sections are followed by a discussion of animal, cadaveric, and epidemiological experimentation for assessment of BABT. BABT Injury Mechanisms Thoracic anatomy, as shown in Figure 8-5, emphasizes the importance of the thoracic region for BABT. Indeed, ballistic protective measures have been designed specifically to protect this region and portions of this region. The majority of organ systems necessary for life are located in the thorax. The mediastinal region is particularly important. Notable structures in the mediastinum in addition to the heart include major blood vessels (aorta, pulmonary artery, and vein), branch points of the lungs (trachea), and connections to the gastrointestinal system (esophagus). The thorax includes the lungs, which offer a large impact surface area, and the liver, that are not completely protected by the rib cage. On the posterior region of the thorax, the spine presents an additional impact location that is potentially debilitating or life threatening. -178-

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PREPUBLICATION DRAFT—SUBJECT TO EDITORIAL CORRECTION FIGURE 8-5 Human upper torso. There are a number of potential mechanisms for injury that have been seen in animal, cadaver, or human epidemiological studies. These include physiological mechanisms such as commotio cordis (Link et al., 1999) and ARDS (Miller et al., 2002). Commotio cordis, a disruption of heart rhythm that occurs from blunt trauma directly over the heart, is thought to occur during only a small window of the cardiac cycle. So, the risk of such cardiac rhythm disruptions may be small. Several types of injuries may be attributed to tissue displacement. These include large displacements that may cause shear or crushing injuries. These injuries may include puncture caused by bony fracture. An example of this is a fractured rib penetrating into a lung and disrupting the plural cavity, which may result in pneumothorax or hemothorax. Fung et al. (1988) suggested that lung injuries might be related to compression of the alveoli under mechanical stress. However, at high rate, for ultrasonic forcing, the influence of local cavitation has been suggested. Indeed, negative pressures have been seen recently in ballistic animal experiments (Sarron, 2001). Pulsation mechanisms similar to those seen in ultrasound tissue damage may be relevant to BABT tissue damage. For short-duration ultrasound, stress waves and cavitation have been proposed that may be BABT injury mechanisms. Ultrasound impulses involve low displacement with relatively high frequency (50 kHz-1 MHz). The effect of exposure duration on the threshold injury pressure is important (Carstensen et al., 1990) (Figure 8-6). Thresholds for damage in lung tissue in the murine model are significantly lower than those for damage in other tissues, as shown in Figure 8-7, and have been found to be frequency dependent. -179-

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PREPUBLICATION DRAFT—SUBJECT TO EDITORIAL CORRECTION MEDICAL RESEARCH NEEDS The principal biomedical issues relating to the development of a test methodology for soft and hard body armor testing with a strong basis in biomedical response and injury include these:  The response of the clay currently used in the backface impact methodology has limited biomedical basis in human body response. As the human torso responds differently for impacts at different rates, the current clay response methodology has no biomedical basis for hard body armor impacted with high-velocity rifle rounds.  The link to human injury in the current clay methodology was developed for the behind-armor impact of soft armor and has a limited biomedical basis even for soft body armor. The current methodology has no link to human injury for hard body armor impacted with high- velocity rifle rounds.  The backface torso response and the effects of BABT on organs remote from the point of trauma are likely dependent on impact rates for both soft and hard body armor.  There are only very limited links to human epidemiology for injuries from BABT when rifle rounds impact hard body armor worn in combat. This fact combined with the fact provided by DoD that there are no known fatalities from design threats suggests that it is unknown whether body armor is overdesigned against current threats. This has substantial implications for battlefield mobility, thermal loads, and other important issues in combat. In the face of real-world constraints on dollars and manpower, Figure 8-31 provides a prioritized, time-phased road map for the near-term and medium-term medical research that is needed to reach the long-term goal of developing a test methodology for soft and hard body armor based soundly in biomedical response and injury. Near-Term Actions As shown in Figure 8-31, several near-term actions are needed to address the biomedical issues enumerated above and provide a strong biomedical basis for future body armor testing:  The backface response of clay must be tested for its plastic and viscoelastic characteristics and correlated with relevant drop tests as well as animal and human thoracic response. See Recommendation 4-2.  Injury risk assessments for structural and physiological injuries must be developed using animal tests and human cadaver tests for a typical range of hard body armor backface velocities. Experience from the -229-

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PREPUBLICATION DRAFT—SUBJECT TO EDITORIAL CORRECTION limited number of previous animal, cadaveric, and surrogate studies should be assessed to help guide these studies. See Recommendations 8-2 and 8-3.  Tests involving human cadavers or animals must be conducted to determine response behind deforming hard armor for a typical range of hard body armor backface velocities. Experience from the limited number of previous animal, cadaveric, and surrogate studies should be assessed to help guide these studies. See Recommendation 8-2.  A military medical epidemiology database must be established that focuses on ballistic backface trauma vs. penetrating trauma, including non-injury cases to provide information to assess tradeoffs of protection and actual levels of protection in field, See Recommendations 8-1 and 8-5. Medium-Term Actions The near-term actions shown in Figure 8-31 should provide input to medium-term medical research to produce a biofidelic test methodology for soft and hard body armor. Key medium-term actions are an assessment of the biofidelity of the clay test method and development of instrumented response elements. Specifically,  Assess the biofidelity of the clay or other alternative test method using near-term research results. See Recommendation 8-6.  Develop an alternative to the clay methodology using digital sensors with a thorax response element. See Recommendation 8-7.  Develop detailed anatomical surrogates. See Recommendation 8-8. The long-term goal is to improve body armor by choices of materials and system configurations so the weight and protection are optimized. To reach this goal, a practical biofidelic test methodology for both soft and hard body armor is essential. -230-

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PREPUBLICATION DRAFT—SUBJECT TO EDITORIAL CORRECTION REFERENCES Akimov, G.A, M.M. Odinak, S.A. Zhivolupov, B.S. Glushkov, and T.I. Milovanova. 1993. The mechanisms of the injuries to the nerve trunks in gunshot wounds of the extremities. (experimental research) (article in Russian). Voennomeditsinskii Zhurnal (Military Medical Journal) 80(9):34- 36. Axelsson, H., H. Hjelmqvist, A. Merdin, J.H. Persson, and A. Suneson. 2000. Physiological changes in pigs exposed to a blast wave from a detonating high- explosive charge. Military Medicine 165:119-126. Axelsson, H. and J.T. Yelverton. 1996. Chest Wall Velocity as a Predictor of Nonauditory Blast Injury in a Complex Wave Environment. The Journal of Trauma: Injury, Infection, and Critical Care 40(3S): 31S-37S. Baker, S.P., B. O'Neill, W. Haddon Jr, and W.B. Long. 1974. The injury severity score: A method for describing patients with multiple injuries and evaluating emergency care. Journal of Trauma 14(3):187-196. Barwood, M., P. Newton, and M. Tipton. 2009. Ventilated vest and tolerance for intermittent exercise in hot, dry conditions with military clothing. Aviation, Space, and Environmental Medicine 80(4):353-359. Bass, C.R., S.M. Duma, J.R. Crandall, W.D. Pilkey, N. Khaewpong, R.H. Eppinger, and S. Kuppa. 1997. Interaction of air bags with cadaveric upper extremities. Journal of Passenger Cars, SAE Transactions 106:3644-3650. Bass, C.R., J.R. Crandall, C. Wang, W.D. Pilkey, and C. Chou. 1998. Open-loop chestbands for dynamic deformation measurements. Journal of Passenger Cars, SAE Transactions 107(6):1380-1387. Bass, C.R. 2000. Development of a procedure for evaluating demining protective equipment. Journal of Mine Action, Version 4.2. Available online at http://maic.jmu.edu/journal/4.2/Focus/Bass/bass.htm. Last accessed February 24, 2011. Bass, C.R., B. Boggess, M. Davis, E. Sanderson, G. Di Marco, and C. Chichester. 2000. A methodology for evaluating demining personal protective ensembles for AP landmines. UXO/Countermine Conference, New Orleans, La. Bass, C.R., M. Bolduc, and S. Waclawik. 2002. Development of a nonpenetrting, 9 mm, ballistic trauma test method. Personal Armor Systems Symposium, Colchester, U.K. -231-

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