To summarize, essential elements in the development of a procedure for evaluating the risk of injury while wearing demining protective equipment are:
Each of these elements acts to provide an objective criterion for injury and injury performance while ensuring that the resulting criterion is as applicable as possible to the conditions experienced in the real world.
Each of these elements was satisfied in this proposed test methodology. The simulated mines show repeatable pressure time histories, and the largest simulated mine is comparable to an actual mine of the same threat level. Mine burial can be controlled very precisely, and soil characteristics have been fixed.
The Hybrid III dummy has been found to be a robust and repeatable surrogate. None of the dummies used suffered a significant mechanical failure during the testing. The dummies are available in sizes that are anthropometrically similar to a human mid-sized male and similar to a small female. Positioning was accomplished to within �3 mm relative to the center of the mine with an inexpensive measurement device. Both the kneeling and the prone positions were specified to produce a significant risk of blunt head trauma to an unprotected dummy.
At first glance, it appears that the prone position has a higher risk of neck injury than does the kneeling position. However, it is important to realize the significant difference in nose-to-mine distance for the two positions. For the kneeling position, the dummy�s nose-to-mine distance is 65 cm, whereas for the prone position, the distance is reduced to 45 cm. The two positions were not selected so that the injury risks for the head, neck, and thorax were nearly equivalent, but to directly compare risk of injury between the kneeling and prone positions.
Most of the instrumentation proved robust. For the head and chest accelerometers, the only failures arose from inadvertent wire separation. The head accelerations experienced by the dummies showed a substantial risk of serious head injury from blunt trauma for the larger mines. However, questions remain about the applicability of typical acceleration based injury criteria to mine blasts. It is recommended that a limited test series be performed with an injury model under blast loading to determine the boundaries of applicability of the currently used injury criteria.
The neck sensors performed well. The neck showed forcing similar to that seen in automobile impacts for which the sensors were developed. The sensor data showed good differentiation between the level of mine, and was repeatable within a test dummy. The loosening of the neck of Dummy B compromised the comparison of Dummy A to Dummy B for neck loading. This indicates the large vibration loads in blast shock loading, not seen in the usual automotive application. For future tests, it is strongly recommended that the dummy neck tensioning be checked regularly during the test series.
The thoracic instrumentation proved generally robust. However, neither the chest displacement nor the Viscous Criterion showed injurious values, even for an unprotected dummy. The sternal accelerometers performed poorly, likely owing to high frequency oscillations in the sternum under blast loading. In future testing, the accelerometer should be mounted on the top of the sternum to avoid some of these oscillations. The upper thoracic pressure sensors proved robust, while the lower pressure sensors failed repeatedly. This may be the result of the greater compliance of the Hybrid III dummy in the lower thorax. All PPEs but one reduced the peak thoracic pressure for both the 100 g and 200 g charge size.
The ear pressure sensors proved relatively robust. Surprisingly, two PPEs with the largest helmets showed increased ear peak pressures relative to the unprotected dummy. This may be attributed to the helmets capturing the pressure wave.
Burn sensors used on the dummy hand and chin in this testing showed a very small risk of serious burns for the mines and depth of burial used. As the sensors are exceedingly delicate for blast testing, it is recommended that no burn sensors be used in subsequent testing.
Finally, this testing showed the strong effect of the blast cone induced by the geometry of the mines and simulated mines. This conical blast pattern limited the risk of injury to the thorax in both the kneeling and the prone positions. To provide the most comprehensive understanding of this effect, a small test series should be performed to quantify dummy response as a function of position in the blast cone.
Design of personal protective equipment against fragment and blast damage when demining involves numerous tradeoffs between protection of various types and ease of use. Such tradeoffs underscore the value of a complete assessment of PPE function that includes ergonomics, protection against fragments and protection against blunt trauma.