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2. Test Setup, Test Equipment and Personal Protective Equipment

 

The tests were designed to investigate the suitability of the test methodology chosen to evaluate the risk of injury, especially blunt trauma injury to a deminer wearing a PPE.  The PPEs were chosen to represent a range of styles of commercially available PPEs, and the mines were chosen to represent a range of common antipersonnel mine threats.  In subsequent sections, the test setup, test equipment, mines, and PPEs are detailed.

 

2.1 Test Matrix

 

The test matrix for this study included three primary test variables.  These included charge weight, level of PPE protection, and position relative to the center of the mine blast (kneeling vs. prone) as shown in Table 2 using two nominally identical Hybrid III 50^th % male dummies.  In addition, several tests were performed with a 5^th % female dummy to investigate the effect of smaller body mass and stature.  These tests will be reported separately. 

 

Five styles of PPE suits were tested in 102 blast tests against two simulated mines and one actual mine.  These suits were identified as PPE 1 � PPE 5 as discussed below.  Baseline tests were performed on unprotected dummies for each position and for each of the simulated mines.  The same tests were then repeated with the dummies dressed with each PPE.  The threats used in this test series were simulated mines that contain 50 g, 100 g, and 200 g of C-4.  The Soviet PMN antipersonnel mine was used on 10 shots for comparison explosive yield using two of the PPE styles.  Further details on the PPE styles and mines are reported below.  The test dummies were placed in two common demining positions, kneeling (k) and prone (p).  To enhance the statistical significance of the test data, three shots were performed for each combination of position, threat, and PPE.  Full test conditions for each test in this series are reported in Appendix A.

 

Table 2: Test Matrix for the Hybrid III 50^th %  Male Dummy (Number of Shots, P=Prone, K=Kneeling)

 

2.2 Suits

 

The five PPE suits chosen for this test series represent the range of demining protective equipment that is commercially available.  PPE 1 has a one-piece apron type upper body armor and a visor with a head strap to maintain stability as shown in Figure 10.  PPE 2 (Figure 11) consists of vest type upper body armor with small shoulder wings, groin protection extension, and a visor with head strap that is similar to PPE 1.  PPE 3 (Figure 12) has a more elaborate jacket, containing shoulder wings, groin protection extension, and removable ballistic inserts for washing ease, and chaps style trousers for frontal leg protection.   The ballistic inserts are located in the upper and lower legs, chest, groin, and main body of the suit.  PPE 3 also has a lightweight helmet with chinstrap and visor.  PPE 4 (Figure 13) has a vest with brachial artery arm guards (shoulder wings), lower area groin guard, and a heavy helmet with chinstrap and visor.  PPE 5 (Figure 14) has an elaborate vest, with shoulder wings and groin protector, and shorts for frontal upper leg protection.  PPE 5 also has a heavy helmet with chinstrap and a shorter (smaller frontal area) visor. Protective equipment was placed on the dummies as per manufacturers� instructions to ensure consistent placement and provide consistent coverage.   To assess the potential for upper extremity damage from the mine blasts, surgical gloves were used and penetrations of the latex were noted.

 

Table 3 lists PPE component weights of the suits and visor projected areas.  For blunt trauma protection against mine blasts there is a significant tradeoff between ergonomics and protection.  For instance, a larger mass helmet may provide greater protection against blunt force trauma, but may be more difficult to wear.  Such tradeoffs underscore the value of a complete assessment of PPE function that includes ergonomics, protection against fragments, and protection against blunt trauma.

 

 

Figure 10: PPE 1

 

 

Figure 11: PPE 2

 

 

 

Figure 12: PPE 3

 

 

 

 

 

Figure 13: PPE 4

 

 

 

Figure 14: PPE 5

 

Table 3: Suit Weights

 

Post-shot damage assessment was conducted immediately following the shot and initial safety period.  The initial damage assessment included photographic documentation; inspection of suit, dummy, and instrumentation; and preliminary evaluation of acquired data. The dummies were dressed in woven cotton trousers and shirts beneath the PPE to enable detection of fragmentation penetration. Each piece of PPE was thoroughly examined for tearing, fragment penetration or partial penetration, and overall integrity.  Damaged PPE components were replaced as required; helmets and visors were replaced every shot.  Detailed damage assessments from each shot are presented in Appendix D.

 

2.3 Mines

 

Modeling the mine blast itself is a complicated issue.  Nominally identical mines may have widely different behavior, and blast characteristics may change considerably depending on soil and environmental conditions. Also, real mines may be difficult to obtain in quantity and to handle safely.  To develop an objective test procedure, a test condition should be realistic yet repeatable, a balance that limits the number of tests and cost necessary to effectively characterize the performance of protective equipment.  This suggests that mines should be simulated with a relatively well-characterized plastic explosive and should be implanted in a well-characterized soil.   Several blast energies may be used to simulate the range of energies expected with actual mines.

 

In this study antipersonnel landmines were simulated using 50, 100, and 200 grams of C-4 packed in plastic containers that simulate deployed landmines as shown in Figure 15.  The simulated mines were selected to best represent effects of the broad spectrum of actual antipersonnel mines worldwide and to provide better repeatability from test to test [Bergeron-2000].  The simulated mines were statically detonated using two layers of DETA sheet and a high voltage RP-80 detonator.  The mine molds were provided by Night Vision Laboratories (NVL) and were packed with C-4 and assembled by Aberdeen Test Center (ATC).  The weights of C-4 and DETA sheet for each simulated mine were recorded on each data collection sheet.  A commonly used antipersonnel mine, PMN, was used on 10 shots for comparison as shown in Figure 16.   The PMN mines were statically detonated with a booster composed of C-4 and DETA sheet (RDX based explosive) and an RP-80 detonator. 

 

To provide a repeatable and well-characterized environment for the mine blast, a 61 cm x 61 cm x 61 cm steel open top box was placed within the base of the positioning apparatus in front of the dummy and was filled with medium-grain building sand.  The mines were buried 2 cm below the surface of the sand and were statically detonated.  Damaged sand was removed after each shot and replaced. For efficiency, two shots were set up and fired simultaneously throughout the test series.

 

To assess mine performance relative to an actual mine, tests were performed using a statically detonated PMN mines and the simulated mines.  A free field pressure sensor was used to record the pressure time history of the blast at a location 124 (� 1) cm horizontally from the center of the mine at the level of the ear as shown in Figure 17.  Except for the 50 g mine, each condition had large numbers of mine shots and relatively small spreads in both pressure peaks and integrated impulse.  In addition, pressure peaks and integrated impulse were statistically different between the three levels of simulated mine.  Further, both pressure peak and impulse from the 200 g mine were very similar to the PMN mine, suggesting similar free field behavior for the actual and the simulated mines.  These results give an initial indication of robustness of response, repeatability, and differentiation between three levels of charge.

 

One significant effect of the confinement of the blast by the soil in both the simulated mine and the PMN mine is the existence of a �blast cone� as seen clearly in Figure 9 [c.f. Bergeron-2000].  This is a conical region above the mine in which the blast ejecta and streaming flow is substantially more forceful than outside this region.  This blast cone makes the effect of position of the dummy in the field extremely important.  Further discussion of the physical effects of mine performance within the blast cone is reported below.

 

Figure 15: Simulated Mines

Figure 16: PMN Mine

Figure 17: Peak Pressure and Impulse from Reference Pressure Gauge

 

2.4 Dummies, Test Fixture, and Positioning

 

Dummies

 

Two pedestrian version 50^th percentile male Hybrid III anthropomorphic dummies (A) and (B) were used in this test series. Both Hybrid III dummies used a Hybrid III head/neck complex mounted on a standard Hybrid III upper neck load cell.  The Hybrid III 50^th percentile male is shown in Figure 18.  A Hybrid III 5^th percentile female dummy was used in selected shots (6A through 6D) to represent the deminers from around the world with a smaller body build.  The dummies were placed in each of two positions, kneeling and prone. Owing to variations in dummy response with temperature, the internal temperature of each dummy was monitored, and the dummies were stored in a temperature-controlled environment at approximately 72�F overnight and on non-test days.

 

The Hybrid III dummy was selected for this test series because new development of biofidelic surrogates can be extraordinarily expensive.  The Hybrid III series is widely used in the automobile industry for evaluation of the effects of blunt trauma on humans, so there are preexisting injury criteria that may be appropriate in evaluating injuries from mine blasts.  In addition, the dummies are relatively inexpensive and robust for repeated impacts.

 

Figure 18: Hybrid III Dummy.

 

Test Fixture

 

The test was conducted at the main front Barricade 3 Test Site at Aberdeen Test Center as shown in Figure 20.  Two blast resistant positioning fixtures as drawn in Figure 19 were used to support and to position the dummies and were placed at least 4 meters from the wall and from each other to prevent blast interference. These positioning fixtures were developed by a U.S.-Canadian collaboration including U.S. Army CECOM, Canadian Center for Mine Action Technologies (CCMAT), U.S. Army Aberdeen Test Center (ATC), and the University of Virginia.  They allow accurate positioning for each shot to within � 3 mm of reference locations in each spatial axis.

 

 

Figure 19: Positioning Fixture Drawing

 

 

 

Figure 20: Barricade 3 Test Site Plan View

 

Dummy Positioning

 

Accurate positioning is crucial to ensure repeatability of response and to allow an effective evaluation of the performance of a demining PPE for two principal reasons.  First, the strength of the mine blast falls rapidly with distance from the mine in the near field.  Second, soil confinement of the mine blast imposes a �blast cone� which includes the most forceful, streaming component of the blast.  The test fixture constructed for this study is based on a design produced by a U.S. � Canadian collaboration reported by Nerenberg et al [Nerenberg-2001] used in previous PPE testing as shown in Figure 21.

 

Accurate positioning of the dummy relative to the center of the mine was performed using a measurement fixture, also shown in Figure 21 for the kneeling position, that allows repeatable positioning of both the mine and the dummy to within approximately �3 mm of fixed reference points.  The measurement fixture incorporated two sliding measurement arms to locate the reference points at the dummy nose and sternum center in a rectangular coordinate system with the origin at the center of the mine with an accuracy of approximately �1 mm.  To ensure accurate mine placement relative to the test fixture, a cylindrical form on the base of the measurement unit was used to create a hole in the sand for mine placement. The form fit inside a sleeve, which remained for mine placement when the measurement fixture was removed.  After the mine was placed in the sleeve, the sleeve was removed, and the mine was covered with 2 cm of sand (flush with the side rails of the positioning fixture).  Three forms with matching sleeves were used, one for each simulated mine size.   The largest simulated mine size matched the PMN mine.

 

Both the kneeling and the prone positions were selected to establish a baseline position that was severe enough to produce a significant risk of injury in the unprotected dummy, but not too severe that the dummy could be damaged or that the most protective of the PPEs could not reduce the injury criteria values.  The nominal kneeling position, evaluated using an accurate three-dimensional contouring tool, is shown in Figure 23. The dummy was positioned using chains attached to the upper spine, which allow free motion to the rear under a mine blast.  The dummy maintains lower extremity position using normal joint friction.  After positioning the unprotected dummy in the kneeling or prone position, the measurement fixture was used to record distances from the center of the mine. For the dressed tests, after the nose and sternum were set in place, the dummy was dressed in the PPE.  The body armor and visor were then set to selected distances from the mine.  For the kneeling position, the radial nose-to-mine distance was set to 70 cm at an angle 65⁰ from the mine with x (horizontal) and z (vertical) coordinates as shown in Table  4. The radial sternum-to-mine distance was set at 64 cm with coordinates shown in Table 4.

 

Table 4: Coordinates for Reference Positions Tested (NM = Not Measured)

For the prone position shown in Figure  22, the positioning fixture is not used. Instead, the dummy is balanced on the elbows, and position is maintained by normal joint friction. To produce potentially injurious head accelerations in the unprotected dummy, the radial distance is significantly decreased to 45 cm, at an angle of 48⁰ vertically from the mine.   Coordinates are shown in Table  4.  For several preliminary shots, additional kneeling and prone positions were tested as shown in Appendix A.

 

The Hybrid III dummy was modified to increase the range of motion in both the lower cervical spine and the lower lumbar spine to enable the dummy to assume a realistic prone position with approximate biofidelic spine extension. Human range of motion in extension is approximately 35 degrees in the lumbar spine, approximately 25 degrees in the thorax, and approximately 50 degrees in the neck.  Since the Hybrid III dummy has a limited number of locations to add additional extension, a 30 degree wedge was inserted above the flexible lumbar spine.  In addition, the slot in the adjustable lower neck mount was elongated to allow a total of 22.5 degrees in extension from the neutral position.  Use of these adjustments produced an approximately realistic Hybrid III dummy prone position as shown in Figure  22.  Drawings and photos of these mounts are shown in Appendix B.

 

Figure 21: Kneeling Dummy with Positioning and Measuring Fixtures

 

 

 

Figure 22: Prone Dummy with Positioning and Measuring Fixtures (Note:  Positioning Fixture Not Used for the Prone Position)

 

 

Figure 23: Nominal Kneeling and Prone Positions Relative to the Center of the Mine - Radial Lines at 30⁰ and 60⁰

 

2.5 Instrumentation and Data Acquisition

 

Hybrid III anthropomorphic dummies were instrumented to measure temperature, pressure, sternum acceleration, neck moments and forces, and acceleration in the head and chest as shown in Table 5.  Triaxial acceleration data were collected at head and chest locations.  Upper neck load cells measured forces and moments in the x, y, and z axes from frontal, lateral, or combined impacts.  Also, pressure sensors were used in the thorax and head to determine the risk of blast injuries to the lungs and ears.  For the first few shots, thermocouple sensors were embedded in a skin simulant constructed of urea formaldehyde (Beetle) molded resin and attached to the dummies� skin on the hand to determine risk of burn injuries (as shown in Figure  24.).  The technique showed that at all explosive levels, no sensor signal exceeded the burn injury threshold and was not used for the remainder of the test series.  For all signals, the sampling frequency was 200 kHz with antialiasing filtering at 40 kHz.  After each shot, sensors were inspected for damage and were replaced as required.

 

 

Transducer	Location	Data Collected	Notes
Accelerometer	Head CG	Triaxial acceleration	Endevco 7270A-6k
	Chest CG	Triaxial acceleration	Endevco 7270A-6k
Load Cell	Upper neck	Mx, My, Mz and Fx, Fy, Fz	Frontal, lateral, or combined impacts.
Accelerometers	Sternum	Acceleration	Chest acceleration Endevco 7270A-6k
Displacement Transducer	Sternum	Displacement in x	Chest deflection.
Pressure Transducer	Thorax:  skin surface, between 3rd and 4th rib	Pressure-frontal impact and side on	Kulite XCQ-093-500A Kulite LQ-125-500A
	Head, skin surface, mounted laterally at ear location	Pressure	Kulite XCQ-093-500A
Thermocouple in Skin Simulant Figure 24	1 each, thorax, head, hand	Temperature	Omega 0.5 mil and Omega 3 mil bare wire gages.
Pressure Gauges	Free field at the same x y locations as ear and thorax	Pressure	PCB 102-A04
Thermocouple	Spine box	Internal temperature	Static

Table 5: Instrumentation

 

 

Figure 24: Skin Simulant with Embedded Thermocouple

 

 

2.6 Photography

Two high-speed video cameras, a Kodak 4540 and a Kodak HG 2000, were used to document blast evolution and dummy response during each shot.  The Kodak 4540 black and white video camera recording rate was set to 9000 frames per second (fps) while the HG 2000 video camera recording rate was 1000 fps  Pre- and post-test still photographs were taken to record the test setup and to document all PPE and dummy damage.

 

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