Testing of Body Armor Materials Phase III (2012) / Chapter Skim
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8 Medical Basis for Future Body Armor Testing
8 Medical Basis for Future Body Armor Testing
Pages 169-239
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From page 169... ...
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)
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From page 170... ...
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.
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From page 171... ...
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.
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From page 172... ...
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.
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From page 173... ...
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)
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From page 174... ...
Injury risk evaluation. A correlation between an engineering measurement and some injury model.
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From page 175... ...
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.
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From page 176... ...
These data may be used to develop injury models and to focus the development of countermeasures. There are several limitations with epidemiological data.
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From page 177... ...
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.
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From page 178... ...
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.
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From page 179... ...
. 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.
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From page 180... ...
PREPUBLICATION DRAFT -- SUBJECT TO EDITORIAL CORRECTION FIGURE 8-6 Threshold pressures and exposure times needed to damage drosophila larvae using various loading devices. SOURCE: Carstensen, 1990.
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From page 181... ...
. Damage from the transmission of kinetic energy from the point of impact on the torso to remote body organs in humans has been observed in a number of cases (Carroll and Soderstrum, 1978; -181
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From page 182... ...
, although the Fung hypothesis might be more relevant to posttraumatic lung edema. Mechanical Correlates with Injury An injury criterion might be used to study and categorize blunt trauma if developed with a physical measure (e.g., acceleration)
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From page 183... ...
Its drawback is that it is a simple global model that is unlikely to represent the local interactions that actually cause injury and so may be misleading in certain circumstances, such as blunt trauma from small projectiles. FIGURE 8-8 The Adjusted Severity of Injury Index values versus peak inward chest wall velocity.
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From page 184... ...
These thresholds may be a benchmark for injuries that occur from very sharp initial peak pressures owing to differences in acoustic impedance between the back of the body armor and the thorax. This is discussed further in the context of the Oksbøl animal experiments below.
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From page 185... ...
The most widely used criteria for thoracic injury are the compression criterion and the viscous criterion for frontal impacts and the thoracic trauma index for side impacts. The compression criterion relates the relative chest deformation with respect to the chest depth to the level of injury.
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From page 186... ...
TABLE 8-3 Description of Levels of Thoracic Trauma Level of Trauma Nature of Injuries I (slight) Scratches on the skin, ecchymoses, and restricted subcutaneous haematomas.
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From page 187... ...
, firing distance, and impact kinetic energy. Bullet kinetic energy was plotted against injury severity for both human epidemiology and animal experiments, as shown in Figure 8-10.
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From page 188... ...
within 6 hours of the mine blast injury (Figure 8-11)
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From page 189... ...
PREPUBLICATION DRAFT -- SUBJECT TO EDITORIAL CORRECTION FIGURE 8-11 Time of delivery of wounded to the CMH (average 1983-1984)
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From page 190... ...
PREPUBLICATION DRAFT -- SUBJECT TO EDITORIAL CORRECTION FIGURE 8-12 Severity of wounds for patients delivered to the CMH (average 19831984)
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From page 191... ...
It is necessary to determine whether the standard is overly conservative and how to assess trade-offs of weight and mobility against protection from ballistic threats. Large Animal Experiments for Behind-Armor Blunt Trauma Animal experiments may be used for the development of injury criteria for blunt trauma, including BABT.
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From page 192... ...
(1966) report experiments on dogs with the lateral thorax impacted by nonpenetrating missiles as shown in Figure 8-13.
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From page 193... ...
The increased lung mass of the animals measured postmortem has some limitations as an injury measure, because bleeding into the lung occurs most effectively while the animal is living. However, over the limited time that the study followed the test animals, the correlation is relatively good.
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From page 194... ...
Danish Army Combat School Animal experiments were performed to assess the potential for thoracic injury from BABT behind undefeated body armor. As reported by Knudsen and Gøtze (1997)
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From page 195... ...
The extensive test series was designed to discern the cause of wounding, by separating the effects of the initial large, short-duration pressure peak from the effects of a secondary displacement pressure peak, presumably caused by the deformation of the body wall behind the body armor. The three body armor configurations are shown in Figure 8-15.
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From page 196... ...
decreased the second peak but also reduced the first peak pressure. Second-peak-only (G2)
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From page 197... ...
All animals tested were injured; however, injury scaling is difficult. The typical injury criterion used in automobile blunt trauma, AIS, is not specific enough to delineate wounding behavior in the Oksbøl series.
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From page 198... ...
This suggests that the local lung damage may be due to transmission of a highamplitude pressure wave. Indeed, lung mass injury from the Oksbøl tests scales directly with the first peak only.
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From page 199... ...
The results showed significant injury and a high mortality for most of the study groups, along with surprisingly significant thorax and lung injuries from hard armor having areal densities up to 24 kg/m2 with foam backing. Pressure and accelerometer recordings were incomplete as the majority of studies experienced saturation of the instruments with pressures exceeding 34 MPa.
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From page 200... ...
As with most NATO-supported animal experiments, the DGA animals were not observed for a substantial time posttest. This prevents the investigation of such injuries as ARDS and others that require long-term physiological monitoring for symptoms to develop.
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From page 201... ...
A shock wave arrives before significant displacements, and pressures are not correlated with the local displacements. From the extensive studies in anesthetized pigs by the French investigators reported in a NATO summary of international studies (Mayorga et al., 2010)
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From page 202... ...
200 Lung Contusion Area (cm2) 150 100 50 0 -50 10 20 30 40 50 60 Penetration Depth (mm)
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From page 203... ...
In order to find a correlation between intrathoracic pressure, BABT, and high- vs low-velocity bullets, 20 pigs, protected by a NIJ Level 3 or 4 bulletproof vest, were shot with 7.62 mm NATO bullets (2.4 kJ and 3.2 kJ) , and 10 unprotected pigs were shot by air gun with 40 mm rubber projectiles (0.07 to 0.2 kJ)
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From page 204... ...
Injuries received included superficial wounds, rib fractures, hemorrhages, and deep lacerations. The tests were correlated to both cadaveric tests and a limited epidemiology as discussed in the section on cadaveric experiments for BABT below.
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From page 205... ...
. The most recent Swedish studies evaluated the efficacy of adding lightweight material to hard body armor to attenuate the transmission of pressure waves (Sondén et al., 2009)
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From page 206... ...
Another important live-animal study of blunt trauma used impactors with velocities from 16 to 94 m/sec in anesthetized pigs (Cripps, 1996)
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From page 207... ...
Recent results (Wood et al., 2010) show that NIJ Level 2 and Level 4 police-issue ballistic vests substantially reduce the peak overpressure of primary blast waves.
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From page 208... ...
Discrepancies between published measurements of pressure changes in intrathoracic pressure for human subjects exposed to blasts from explosives with and without vests needs to be resolved. In the current threat environment, protection against blasts must be considered at least as important as ballistic impact protection, and the relationship between the two threats needs to be better understood.
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From page 209... ...
Instrumentation included accelerometers at the sternum, T7, carina, and ligamentum arteriosum, as well as pressure transducers in the right and the left heart ventricle, and the left chest. Measurements of the impact pressure between the armor and chest wall were reported as not reliable.
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From page 210... ...
BABT Injuries Behind Hard Armor A highly deforming hard body armor study to estimate the mechanical correlates with BABT injury in nine cadavers and two anthropomorphic test dummies used a range of velocities including low-severity impacts, mediumseverity impacts, and high-severity impacts based upon risk of sternal fracture (Bass et al., 2006)
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From page 211... ...
Thus, damage to such organs as the intestines, spinal cord, brain, or vascular system from transmitted pressures associated with blunt trauma cannot be predicted. Recommendation 8-2: The Army should perform high-speed ballistic tests using human cadavers and large animal cadavers to provide responses to deforming hard armor impacted by velocities likely to be encountered in combat.
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From page 212... ...
. It should be noted that a causal connection between pressure waves from explosives or nonpenetrating blunt trauma and cognitive or psychiatric disorders is not the topic of this report, although this subject of blast-induced traumatic brain injury remains an area for intense scrutiny, as exemplified by the conclusions of a recent National Institutes of Health workshop (Hicks et al., 2010)
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From page 213... ...
The third class is "instrumented detailed anatomical surrogates." These generally include some form of thoracic viscera and are designed to investigate a wide range of blunt trauma kinetic energies and projectile diameters.
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From page 214... ...
However, it is advisable to use a relatively inexpensive bulk tissue simulant or instrumented response element for production testing, because in multiple tests there is a potential for penetrating events that can destroy a test device worth thousands or tens of thousands of dollars. Each class of device may have an advantage for a given test condition.
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From page 215... ...
has developed a test device intended to evaluate the injury effect of behind-armor blunt trauma, called the DERA BABT rig (Tam et al., 2000)
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From page 216... ...
Peak accelerations were comparable between the BABT rig and lateral pig shots. These accelerations were approximately 20,000 g for the 7.62-mm test round and the Improved Northern Ireland Body Armour.
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From page 217... ...
The brittle, strain-sensitive paper indicates the level of strain inside the simulant to approximate the temporary cavity during penetrating injury and to determine the extent of local deformation from blunt trauma. There is no electronic instrumentation for this simulator; penetration or injury is indicated by paper between layers.
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From page 218... ...
Use of the Hybrid III dummy has several advantages: It is widely used and is manufactured in several different sizes representative of various standard anthropometries. There are substantial drawbacks to the use of the Hybrid III as a ballistic BABT test device.
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From page 219... ...
Army Medical Research and Materiel Command developed an anthropomorphic test module (ATM) as an instrumented response element for BABT injury assessment, as shown in Figure 8-27.62 The shoulders of the torso are not instrumented but provide an anthropometrically correct platform for mounting body armor as worn by soldiers.
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From page 220... ...
Army Medical Research and Materiel Command, "Blunt Trauma Research to Support a New Body Armor Blunt Trauma Performance Standard and Testing Method," presentation to the committee, August 11, 2010. Essential elements of the ATM methodology include these: The development of a detailed anatomical finite-element model of the human torso (Figure 8-28)
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From page 221... ...
SOURCE: Michael Leggieri, Director, DoD Blast Injury Research Program Coordinating Office, U.S. Army Medical Research and Materiel Command, "Blunt Trauma Research to Support a New Body Armor Blunt Trauma Performance Standard and Testing Method," presentation to the committee, August 11, 2010.
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From page 222... ...
The lungs are simulated by open cell foam as are a heart and liver. In addition, the design includes a mount for a Hybrid III head and neck to allow neck injury assessment.
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From page 223... ...
Experiments on this model were performed using a shock tube, a pendulum device, and ballistic impact behind body armor. Test rounds included 7.62 mm at 870 m/sec in both soft point and full metal jacket, a 9-mm submachine gun at 430 m/sec, and a 37-mm antiriot baton round at 76 m/sec.
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From page 224... ...
An injury scale for intra-lung pressure was developed using pendulum impacts with velocities of approximately 5 m/sec that are stroke limited to 10 percent thoracic compression. Researchers found that the blast pressure peaks were far larger in the blast experiments than in the impact experiments for similar levels of lung damage.
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From page 225... ...
Developmental Testing Requirements In sum, there are several existing test devices that are potentially suitable for use in the development of a test methodology for ballistic BABT. None is currently suitable for use as a test device for BABT with hard body armor without further development or experimentation.
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From page 226... ...
This should include collection of both injury and noninjury events and should be similar to the federal crash databases used by the Department of Transportation -- for example, the Fatality Analysis Reporting System and the National Automotive Sampling System for traffic injuries/fatalities, including injuries induced by both penetrations and backface deformations. Recommendation 8-6: Using experimentally determined links to injury, response, and epidemiology, the Army should ensure that the clay or other alternative test methodology for hard body armor has humanlike dynamic response and is suitable for the development of behind-armor blunt trauma injury criteria.
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From page 227... ...
as research devices to evaluate behind-armor blunt trauma.
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From page 228... ...
PREPUBLICATION DRAFT -- SUBJECT TO EDITORIAL CORRECTION FIGURE 8-31 Road map showing suggested near-term and medium-term research needs, and a long-term goal to provide the fundamental medical basis for injury risk assessment behind helmets and hard body armor.
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From page 229... ...
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.
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From page 230... ...
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.
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From page 231... ...
1996. Chest Wall Velocity as a Predictor of Nonauditory Blast Injury in a Complex Wave Environment.
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From page 232... ...
2000. Thoracic wall response to nonpenetrating balistic injury: The validation of a physical model of behind armor blunt trauma.
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From page 233... ...
1975. Blunt Trauma Data Correlation.
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From page 234... ...
2007. Severe lung contusion and death after high-velocity behind-armor blunt trauma: Relation to protection level.
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From page 235... ...
1988. Some observations relating to behind-body armour blunt trauma effects caused by ballistic impact.
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From page 236... ...
2008. Assessing behind armor blunt trauma (BABT)
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From page 237... ...
2010. Intrathoracic pressure impulse predicts pulmonary contusion volume in ballistic blunt thoracic trauma.
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From page 238... ...
2009. Trauma attenuating backing improves protection against behind armor blunt trauma.
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From page 239... ...
2010. Attenuation of blast overpressure behind ballistic protective vests.
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