3. Injury Criteria and Dummy Response
Sensor data from the mine blasts into the unprotected dummies was examined for repeatability and dummy-to-dummy variation. This includes tests both with and without a PPE.� The principal areas reported below are head blunt trauma, neck blunt trauma, thoracic blunt trauma, and burns.� A key issue in the evaluation of the blunt injury data is whether the standard injury criteria for the Hybrid III dummies may be successfully used since the dynamic time scale of the blast is different than that of automobile crashes.
To provide effective simulation of injuries actually received in mine blast incidents, the types of injuries evaluated should be blunt head trauma, blunt neck trauma, blunt thorax trauma, blast lung, blast-induced hearing damage, and burns.� Blunt injuries can also evaluate the potential for �fall� type injuries caused by whole body displacement from blasts, though no whole body displacements were seen in this test series owing to the stiffness of the Hybrid III dummy.
In subsequent subsections, the evaluation of injuries using dummy surrogates is discussed.� This discussion includes the presentation of results under these simulated mine blasts using relevant injury criteria appropriate for use with the Hybrid III dummies.
3.1 Overview and PPE Fragment Performance
The blast event was generally short compared to the usual durations of impact events for the Hybrid III dummies.� The pressure response of the blast was completed in a duration much shorter than a ms, with acceleration response being approximately 1 ms or greater.� As the simulated and PMN mines are not fragmentation mines, the PPEs were not expected to undergo substantial penetrations.� The PMN mines did produce fragments from the detonation mechanism and large pieces of the bakelite containers.� However, no penetrations resulted from this fragmentation.� There was only one full penetration of the face shield with PPE 2 in Shot6D, and no complete penetrations of the body armor during the test series.� However, many visors completely separated from the head during the blast event, while this may be protective for blast mines, separation may not be desirable for protection against fragmentation mines.� Full descriptions of the fragment protection of each PPE suit in this test series are reported in Appendix D.
3.2 Head Blunt Trauma Injuries
As shown in the field data above, fatalities from head injuries are very significant in mine blasts.� These injuries may be caused by direct blast impingement on the head, or by blunt trauma from impingement of the protective gear. �One injury criterion commonly used with the Hybrid III dummy head/neck complex is the Head Impact Criterion (HIC) for concussive head injury [Versace-1971] based on the Wayne State Concussive Tolerance Curve [Patrick-1963]. HIC includes the effect of acceleration time history a(t) and the duration of the acceleration.� HIC is defined as:
where t1 and t2 are the initial and final times (in seconds) of the interval during which HIC attains a maximum value. So, HIC includes the effect of head acceleration and duration; when the acceleration is expressed in g's, a HIC value of 1000 is specified as the level for onset of severe head injury.� The maximum time duration of HIC is limited to a specific value, usually 15 ms. Physically, HIC predicts that large accelerations may be tolerated for short times and is evaluated using the head triaxial accelerometer at the head center of gravity. This standard is often used to assess head injury using Hybrid III dummies in frontal impacts. However, HIC is based on human cadaver and animal impact data with durations that are usually 5 milliseconds or greater, with extremely limited data less than 1 millisecond in duration.� The acceleration effects of near field blasts are often shorter than 5 milliseconds, raising serious questions about the applicability of the usual injury criteria to mine blast head trauma.
Head Injury � Unprotected Dummy
HIC values obtained for unprotected, kneeling dummies are shown in Figure 25 for mine blast strengths of 50 g C-4, 100 g C-4, and 200 g C-4.� These HIC values for repeated tests show good repeatability among charge sizes and excellent correlation between Dummy A and Dummy B.� In subsequent analysis, sensor data from these dummies are lumped.� The differences in HIC between charge sizes are statistically significant (p < 0.01) with increasing response for increasing charge size.� Kneeling and prone conditions were selected to produce roughly equivalent head response for an unprotected dummy.� However, the prone position is approximately 25 cm closer to the center of the mine.
For the usual 1650 Hz filter used with acceleration time histories that are components of HIC, only the 200 g simulated mine tests show a high risk of head injury for the unprotected Hybrid III 50th % male dummy.� However, if a 10,000 Hz filter is used as shown in Figure 26, the HIC values increase so that all test conditions now see significantly injurious HIC values well above 1000.� This contrast arises since most of the HIC durations were around 1 millisecond as shown in Figure 27.� This implies that the basic frequency of the blast event is 1000 Hz or higher.� So, the relationship between HIC and actual physical injury for these rapid tests can only be roughly estimated.� Thus it is necessary to establish a physical injury model for high rate blunt trauma and correlate it to the dummy model.
Figure 25: Variation of HIC (1650 Hz) with Unprotected Hybrid III 50th % Male Dummies in the Kneeling Position (Average Values for Repeated Testing)
Figure 26: Variation of HIC (10,000 Hz) with Unprotected Hybrid III 50th % Male Dummies in the Kneeling and Prone Positions (Average Values for Repeated Testing)
Figure 27: Variation of HIC Duration for Unprotected Hybrid III 50th % Male Dummies in the Kneeling and Prone Positions (Average Values for Repeated Testing)
Head Injury � Suited Dummy
HIC values for the tests using kneeling dummies are presented in Figure 28.� As expected, the addition of a PPE helmet to an unprotected dummy improved protection from head trauma for some of the PPEs tested.� Helmets 4 and 5 performed well for both the 100 g and 200 g simulated mines.� The helmet of PPE 3 decreased HIC statistically significantly for the 100g charge only.� Similar trends are seen with the PMN mines and the simulated mines.
Figure 28: HIC Values for Mine Blast into Kneeling Dummy, All Charge Sizes, All PPEs
Unexpectedly, the facial protection with PPE 1 did not reduce the risk of head blunt trauma when compared to the unprotected case.�� The physical features of the head protection gear, including the projected frontal area and the mass (Figure 29) provide an explanation for the substantial increase in HIC values from the unprotected dummy to a dummy protected by PPE 1.� First, the heavier helmet/visor sets produced lower HIC values.� The two heaviest helmets, those from PPE 4 and PPE 5, performed better than those from the other PPEs for dummies in the kneeling position because the larger mass decreases the acceleration of the head, resulting in a smaller HIC value.� The mass of the standard Hybrid III head/neck complex is 5.8 kg.� So, the 2.6 kg mass of the helmet/visor set from PPE 5 adds approximately 45% more weight to the structure, and probably explains the significant drop in HIC when suit 5 armor is added to an unprotected dummy.�
There is, however, an obvious tradeoff for the protective value of added helmet mass.� Increasing the helmet mass without regard for ergonomic factors of wearability of large head supported masses and heating may result in limited usage of the face protection.� Second, larger frontal areas of the helmet/visor sets tended to increase the risk of head injury from mine blasts.� This frontal area dependence arises from the increased exposure to the blast flow; the larger visors can �catch� more of the blast wave and induce larger head accelerations.�
Figure 29: Helmet and Visor Characteristics
Figure 30 presents the results for dummies in the prone position.� Only PPE 5 reduced the HIC for the 200 g charge when compared to the unprotected values.� In all other cases HIC was not significantly different.� Geometric differences between the prone position and the kneeling position produce this difference in injury risk.� The head in the prone position is more upright than in the kneeling position, so the blast streams more tangentially to the surface of the visor.� This decreases the effect of frontal surface area on the HIC value.� However, there is still some evidence of a mass effect as the PPE with larger helmet masses still has lower risk of blunt trauma injury.
Figure 30: HIC Values for Mine Blast into Prone Dummy,
�All Charge Sizes, All PPEs
To further quantify the relationship between the helmet mass, projected frontal area, and HIC, the HIC values were plotted against the helmet parameters and linear curve fits were applied to the data.� Four different data sets were considered: kneeling position, 100g charge; kneeling position, 200g charge; prone position, 100g charge; and prone position, 200g charge.� Each data set had a separate linear curve fit.
The HIC values were plotted against the nondimensional area/mass (cm2/kg) ratio for each PPE helmet and the linear curve fits were determined for the four data sets as shown in Figure 31.� The helmet area is nondimensionalized by the frontal area of a Hybrid III dummy head, and the head/helmet mass is nondimensionalized by the mass of a Hybrid III dummy head.� This ratio of frontal area to mass was chosen because the acceleration of a head under blast pressure loading is directly related to the frontal projected area of the head or helmet, and acceleration under an applied external force is inversely related to the mass of the head/helmet. The average R2 for these fits varied from 0.08 (P100) to 0.79 (K200).� It was easy to distinguish between the 200g and 100g charges on this plot, as the 200g charge data (both kneeling and prone) had much larger slopes than the 100g charge data.�
Figure 31: Variation of HIC with Helmet Frontal Area/Helmet Mass
for Simulated Mines of 100 g and 200 g (K = Kneeling, P = Prone)
3.3 Neck Blunt Trauma Injuries
Neck injuries from blasts are possible owing to different rates of acceleration of the head and of the chest under blast loading.� Physical trauma to the neck may be evaluated using the neck force transducers that may be incorporated into the Hybrid III dummy.� Barring local damage to the neck itself, the dynamic impulse in the neck must be transmitted through the relative motion of the head and the chest.� This transmission of force is relatively slow compared to the impact of the blast wave.� So, neck injuries in blast are similar in rate to impact neck injuries that have been studied in automobile safety and other contexts.� There is a proposed neck injury criterion promulgated by the National Highway Traffic Safety Administration (NHTSA) termed the N�ij criteria [Eppinger-2000].� The criterion is to be used with Hybrid III dummies.
The N�ij criterion is a composite injury indicator based on a linear combination of neck loads and moments.� These loads include neck axial tension and compression, and the moments include neck flexion and extension.� The postulated injury levels for these combined loads have been validated using human cadaver, volunteer, and animal subjects. N�ij is defined as
where Fz is the tension/compression force and Mz is the flexion/extension moment.� The values FINT and MINT are the normalization values for the mode of axial force or bending as shown in Table 6. The hexagonal perimeter in Figure 32 represents the Injury Reference Value (IRV) of Nij = 1.0 that corresponds to a 30% risk of severe neck injury.�� The shaded portion is considered acceptable neck loading by this criterion.
|
Intercept Value |
Hybrid III 50th % Male |
Hybrid III 5th % Female |
|
FINT � Tension (N) |
4170 |
2620 |
|
FINT � Compression (N) |
4000 |
2520 |
|
M�INT � Flexion (N-m) |
310 |
155 |
|
M�INT � Extension (N-m) |
135 |
67 |
|
Peak Tension (N) |
6806 |
4287 |
|
Peak Compression (N) |
6160 |
3880 |
Table 6: Normalized Forces and Moments for Nij Criteria
Figure 32: Nij Criteria for the 50th Percentile Male Dummy [Eppinger, 2000]�
Neck Injury � Unprotected Dummy
The Nij standard injury predictions were used to assess the effects of the particular dummy used on the test results as shown in Figure 33.� Though none of the tests using the unprotected dummies show a high risk of injury indicated by Nij values, there is a significant difference between risk of neck trauma from Dummy A to Dummy B.� For matched tests between Dummy A and Dummy B where sufficient tests were available, there was a statistically significant difference between the neck response of the two dummies.� The Nij criterion is the sum of the effects of both neck tension/compression axial load and neck flexion/extension moment.� However, the configuration of the Hybrid III neck has little axial compliance for loading in tension.� For this series of tests, the maximum value of Nij was, on average, a function of 90% neck extension and only 10% tension, and thus, it is highly dependent on the compliance allowed within the neck by the pretensioning setup of the neck.�
�
After the test series was complete, it was determined that the pretensioning bolt supporting the neck for Dummy B was loose, while Dummy A was within specifications. This resulted in a decreased resistance to extension in Dummy B.� With a looser neck, Dummy B tended to move out of the blast cone over long times, reorienting the applied load and substantially decreasing the moment.� So, only Dummy A was used in further analysis.� As this occurred over relatively long times, this did not affect the head accelerations.
Also seen in Figure 33, Nij levels generally increase with charge size. For all tests the 50 g and 100 g charge sizes are statistically significantly different than the 200 g charge size (p < 0.01).� The prone Nij values are generally larger than the kneeling for two reasons.� First, the prone position is 25 cm closer than the kneeling position to the mine blast, though lower in the blast cone.� And second, the orientation of the head in the prone tests is more normal to the local blast flow, producing an increased neck moment.� So, this result should not be taken as an indication that the prone position has a higher risk of neck injury than the kneeling position for the mines tested.
Figure 33: Effect of Dummy for Matched Tests of an Unprotected Hybrid III 50th % Male Dummy In Both Primary Test Positions And At Three Charge Masses
The strong effect of the blast cone can clearly be seen in additional tests performed at varying distances to the mine and at varying angles within the blast cone.� For the kneeling position, two angular positions of the head and two nose-to-mine distances were examined as shown in Figure 34 for a 100 g simulated mine.� The tip of the nose was used as a reference point for the head position and the two angular positions were 70� and 65� as measured from the horizontal.� The vertical distance to the mine, however, remained relatively constant.� The 5� reduction in angle shifts the loading distribution away from the thorax towards the head alone, creating higher relative loads on the head.� These higher loads produce higher neck flexion moments.�
This result directly contradicts the expectation that increasing radial distance from the blast substantially decreases loading.� The 70� position had a 65 cm radial nose-to-mine distance, while the 65� position had a 70 cm radial nose-to-mine distance; the increased distance tended to increase the overall loading in this range of angles and distances.� This shows the effect of the strongly conical shock, and the importance of evaluating the effects of the blast cone when assessing injury tolerance using this methodology.
Figure 34: Effect of Dummy Position Relative to the Blast Cone (Kneeling Position, 100-g Charge)
For the prone position with a 200 g simulated mine, three angular positions of the head and three nose-to-mine distances were examined (Figure 35).� A constant nose vertical height (33.2 cm) was maintained, and the dummy was moved horizontally relative to the mine position.� The tip of the nose was used as a reference for the head and was placed 50 cm, 37.5 cm, and 30.5 cm horizontally from the center of the mine.� The reduction in angle for the prone position has a slightly different effect than for the kneeling position.� In the prone position there is minimal thoracic loading because of the lower position of the body.� Therefore, the reduction in angle simply moves the head further from the conical blast cone, thus reducing the momentum transferred to the head and the neck flexion moment.
Figure 35: Effect of Dummy Position Relative to the Blast Cone (Prone Position, 200-g Charge)
For all tests conducted, including tests with PPEs, the highest Nij value reported was 0.55, which is well below the 1.0 IRV threshold.� So, there is a small risk of serious neck injury for these mine simulants in the positions selected for testing.�
Neck Injury � Suited Dummy
One primary focus of this study was the evaluation of commercially available personal protection ensembles for use by humanitarian deminers.� Many parameters can influence the effectiveness of the PPEs, including suit/helmet mass, projected area, coverage area, and the position in which they are evaluated.� For a larger projected area, a higher momentum transfer from the blast is transmitted to the head.� However, the additional mass by the helmet increases the inertial resistance of the head/helmet composite, reducing the acceleration and delaying and reducing the peak force applied.� Other variations are a result of the distribution of the projected area of the helmet and faceshield.� The higher the projected area is on the head, the farther the resultant force of the blast is from the neck, thus creating a longer moment arm for the loading to act.
Figure 36 and Figure 37 illustrate the trends in suit performance for neck blunt trauma injuries for the various mine charges in both the kneeling and the prone positions.� Despite the limited number of reportable tests for the dummy suited with one of the PPEs, it is evident that the average value for Nij for all cases (position and charge) is reduced for the protected dummy.� However, some tests did have higher Nij values than the average baseline unprotected dummy.� This is seen, for example, in tests using PPE 3 in the prone position with a 100 g charge (Figure 37).� So, there is a potential for a lightweight visor or visor/helmet combination to add enough projected area to the dummy head without substantial counterbalancing mass that the Nij values would increase for the protected dummy.�� However, the highest Nij value reported for all the tests conducted was 0.55, which is well below the 1.0 IRV threshold.� With the data resulting in such low Nij values, we can conclude that for this test series, there exists a very small risk of serious (AIS � 3) injury.�
Figure 36: Effect of PPE on neck injury for dummy in the kneeling position
Figure 37: Effects of PPE on neck injury for dummy in the prone position
3.5 Thoracic Blunt Trauma Injuries
The blast pressure waves and following pressure wave from the detonation of a mine have the potential to produce severe blunt trauma to a human thorax in proximity to the blast.� Several injury criteria have been developed to characterize the risk of thoracic injury.� One widely used criterion, based on maximum displacement of the chest wall, allows a maximum 63-mm chest deflection in the 50th percentile male Hybrid III dummy [Eppinger-2000].� The displacement of the chest wall can be regarded as a surrogate for local strain within the chest.� Presumably, the larger the local strain within the chest, the more injurious the local impact.�
Another potentially useful injury criterion is the viscous criterion (VC) developed by Viano et al [Viano-1988].� This criterion is the product of the velocity of chest wall displacement (V) and the deformation of the chest relative to the initial thickness of the thorax (C).�� This quantity has been linked with the rate of energy storage in the thorax.� A value greater than 1.0 m/s is considered injurious.
Thoracic Blunt Injuries � Unprotected and Protected Dummy
Displacement chest injury criteria were initially used to assess the effects of many of the test parameters including the charge size, dummy position, and suits.� The peak chest compression for any of the tests was 2.6 mm, which falls significantly below the IRV for chest compression.� The majority of tests produced chest compressions below 1 mm, and the average chest compression for all tests was only 0.6 mm. �These small values lead to two conclusions for the test analysis.� First, there exists a very low risk of chest injury related to compression.� Second, the small compression values are so small that the inherent error of the chest slider mechanism may become significant, thus limiting the statistical trends that may be inferred from the data.
The protective equipment was evaluated relative to the unprotected dummy for both the 100g and 200g charge levels and for both the kneeling and the prone positions (Figure 38 and Figure 39).� As discussed earlier, the peak compression values are significantly below accepted IRVs and have the potential to be significantly affected by the compliance in the sensor itself.� However, one surprising result is that peak chest displacements for several tests with a suited dummy are higher than those for an unsuited dummy.� Therefore it may be concluded that the potential exists that a large profile, low mass thoracic protection suit may actually exacerbate the thoracic loading.
Figure 38: Peak Chest Compression for the Unprotected and Protected
Dummy in the Kneeling Position
Figure 39: Peak Chest Compression for the Unprotected and Protected
Dummy in the Prone Position
For VC, the thoracic displacements are relatively small, and there is no direct measurement of the velocity of the chest.� So, the velocity must be calculated either by integrating a sternal accelerometer mounted to the chest wall, or by differentiating the displacement signal.� In this test series, the sternal accelerometer was used to obtain the velocity. Though the displacement is small, the velocity is relatively high for this test series.� However, the sternal acceleration measurements did not prove robust for this test series. So, the limited numbers of available values for the viscous criterion are shown in Figure 41 for the unprotected dummy.� The values generally increase with increasing explosive blast.� Statistical comparison of the differences between dummies is unavailable, however, because of the limited data set.
For this test series, the conical blast pattern limited the risk of injury to the thorax.� Neither the sternal displacement nor the VC showed values that could be reasonably construed as injurious.
Figure 40: Variation of Chest Maximum VC with Unprotected Hybrid III 50th % Male Dummies in the Kneeling and Prone Positions (Average Values for Repeated Testing)
Figure 41: Variation of Viscous Criterion with Unprotected Hybrid III 50th % Male Dummies in the Kneeling and Prone Positions (Average Values for Repeated Testing)
3.6 Thorax and Head Blast Injuries
There is a substantial risk of blast overpressure injuries, either blast lung or blast-induced hearing injuries, close to antipersonnel mine blasts.� However, the usual instrumentation of the Hybrid III dummy does not include any assessment of the effects of blast overpressure, either in the head or the chest.� So, four pressure sensors were mounted on the surface of the chest to evaluate the potential for blast lung injuries.� These sensors were placed in each quadrant of the thorax.� In addition, a pressure sensor was mounted in a �side on� configuration in a hole in the mid-thorax.� This pressure sensor had limited success owing to the difficulties of mounting such a gauge in the Hybrid III thorax.� Many of the sensor time histories show large peaks that are likely the motion of the gauge in the dummy chest.� Finally, a pressure sensor was mounted in the head at the location of the ear to evaluate the potential for hearing damage.� Owing to the presence of impulsive spikes in the data in all channels, the pressure data was processed using a 15-point median filter.��
The evaluation of blast wave injuries is important since addition of protective equipment for the thorax may exacerbate blast overpressure injuries.�� Experience using body armor in Northern Ireland has shown an increased incidence of blast lung injuries, either from enhancement of the blast wave behind the body armor or from protection from usually fatal damage [Mellor-1989].
Of the four surface mounted thoracic pressure gauges, the lower gauges failed repeatedly early in the test series.� So in the succeeding analysis, the upper right thorax pressure gauge was used.� The peak external pressures for the protected and unprotected dummies at the 100 g and 200 g charge level from the upper left thorax gauges are shown in Figure 42.�� Approximate durations of these pressure time histories are 0.7 ms. These are compared with the threshold lung damage free field values taken from classic work by Bowen et. al. [Bowen-1968]. Both the unprotected and protected dummies show much larger peak pressures for the 200 g charge size than the 100 g charge size.� In addition, all of the dummies with PPEs show decreased peak pressures relative to the unprotected dummies except PPE 2 for the 200 g charge size.� Complex wave interactions behind the PPEs may be the explanation for the large spread in thorax peak pressures for certain PPEs.� However, for both the 100 g and 200 g charge sizes, the peak thorax pressure does not exceed the threshold for blast lung injuries. The complexities of evaluating injury criteria for complex pressure waves suggest the strong need for an experimental effort to evaluate such waves in an injury model.
Figure 42: Peak Thorax Pressure for Kneeling Hybrid III 50th % Male Dummies
The peak ear pressures for the kneeling unprotected and protected Hybrid III 50th % male dummy are shown in Figure 43.� This measurement is similar to a standard �side-on� pressure measurement for which injury thresholds are defined.� For the unprotected dummy, the pressure profiles are similar to an ideal Friedlander pressure wave (instantaneous rise to peak pressure with an exponential decay) seen in free field blasts.� In the protected dummy, there may be streaming flow into the sensor, and there is some evidence of complex flow patterns.� These flow patterns complicate the interpretation of the injury thresholds for ear injuries.� For the tests in this study, the typical duration of the pressure impulse is approximately 0.7 ms. For the 100 g charge, all of the PPEs show comparable or reduced ear pressure peaks when compared with the unprotected dummy.� These peaks are near the threshold for eardrum injury.� However, for the 200 g charge, PPE 3 shows greatly reduced ear pressures while PPE 4 and PPE 5 have peak ear pressures that exceed the 50% risk of eardrum injury.� One reason for these differences may be that PPE 4 and PPE 5 have relatively large helmets that go over the ears with relatively small visors.� This may tend to �capture� the blast wave under the helmet, increasing the peak pressure.
For the prone position shown in Figure 44, however, both the 100 g and 200 g charge peak pressures for the unprotected dummy are comparable to the peak pressures seen with the PPEs.� The reason for the difference between the kneeling and prone results may be the angle of the helmet relative to the blast cone.� The prone dummy is substantially lower in the blast cone, and the dummy head is oriented more perpendicularly to the angle of the blast cone.� So the contribution from the pressure under the helmet and visor may be minimized.
Figure 43: Peak Ear Pressure for Kneeling Hybrid III 50th % Male Dummies
Figure 44: Peak Ear Pressure for Prone Hybrid III 50th % Male Dummies
3.7 Burns
As mine blasts involve explosive deflagration, there is a potential for burns close to mine blasts.� The mechanism for this injury is rapid radiant and convective heat transfer into the skin.� The timescales for this injury, flash burn, are so short that heat transfer from the skin into the body is limited. This test series used an existing skin simulant for evaluating injuries caused by thermal insults [Derksen-1960]. The technique uses a plastic resin 0.05 cm thick with an embedded thermocouple.� The temperature output of the thermocouple was correlated with human injury 120 mm below a living skin surface.� Low profile cylindrical samples of this skin simulant with embedded thermocouples were used in this test series to evaluate the risk of flash burns from the blast.�� These skin simulants were attached to the dummy skin at the chin and on the left hand and were exposed directly to the blast in the unprotected tests.�
Blast phenomena may be measured on timescales of milliseconds while most temperature sensors operate on timescales of seconds.� To obtain the most rapid temperature sensor response, thermocouple wires of 0.5 mil diameter were used.� These wires were fragile for dynamic impact testing, so limited data was collected. The temperature time histories were filtered to 500 Hz to eliminate signals faster than the response time of the thermocouple.� These time histories include tests with 4 unprotected hands, including all 3 charge weights used in this series.� The chin temperature sensor was used for 9 tests, including 3 unprotected tests at the 100 g and 200 g charge weight, and 6 protected tests using 3 different suits.� As there is not sufficient data to differentiate the performance of each suit, they have been lumped together for this analysis.
The induced subcutaneous temperature change in the skin simulant implanted on the dummy hand is shown in Figure 45.� This figure includes data from three 100 g tests and a single 200 g test with 42 cm nominal standoff from the mine to the hand.� Though the average temperature change induced by the blast is substantially larger for the 200 g charge than for the 100 g charge, both are less than 20 0C.� As the duration of the temperature increase is less than 100 milliseconds in all cases, the risk of injury from severe flash burns to the hand appears to be small.� To compare with other widely used injury criteria, a free air temperature of approximately 1100 0C for a duration of 1000 milliseconds is necessary to produce second-degree burns [Ripple-1990].
The induced subcutaneous temperature change in the skin simulant implanted on the dummy chin is shown in Figure 46.� Since the number of tests is limited, there is no differentiation between levels of protection of the chin, and the three helmets used are lumped for the analysis.� The dummy chin temperature sensor is located approximately 70 cm radially from the center of the mine in the apparent blast cone.� For the unprotected chin, the induced temperature change in the sensor increases substantially with charge size.� However, as with the dummy hand, the risk of severe burns appears to be quite small, even with unprotected skin contact from the blast.� Interestingly, though the face shield on the protected dummy appears to provide some protection to the chin for the 100 g charge size, the induced temperature change for the 200 g charge size is similar to that seen in the unprotected dummy.� This may be the result of loss of the face shield early in the test and a subsequent skin temperature elevation.� As the induced temperature differential is likely not injurious for these tests, the loss of the face shield during the blast may have had a limited impact on burn injuries.
The use of the skin simulant with the temperature sensor showed a very small risk of serious flash burns with the explosive and charge sizes used in this testing, even with unprotected skin close to the blast.� This was confirmed by the limited burn damage to the dummy skin over a test series of over fourteen unprotected blasts to each dummy head at radial distances as close as 45 cm to the center of the mine.� Factors outside this study, however, such as more incendiary explosives, delayed or inefficient combustion, may increase the risk of serious burn injuries in actual mine blasts.� Indeed, the depth of burial plays an important role in the amount of afterburn [c.f. Bergeron-1998].
Figure 45: Induced Temperature Change From Blast on Dummy Hand
Figure 46: Induced Temperature Change From Blast on Dummy Chin