AMMTIAC-WSTIAC Journal, Vol. 1, No. 2 - Advanced Materials ...

as the Blunt Criterion (BC) where BC = ln(E/(TDW 1/3 )) in which E is the kinetic energyin Joules of the projectile, T is the thickness incm of tissue under the point of impact, W is themass of the impacted person in kg, and D is thediameter of the projectile in cm. The followingrelationship can be used to estimate T,T=kW 1/3 , where k = 0.711 for males and 0.593for females. The BC has recently been reanalyzedand shown to have a linear relationship tothe Viscous Criterion (VC), 7 when the VC ismeasured for impacts with similar hard, flatnosedcylinders on fresh cadavers. The VC is avalidated method for predicting severity ofblunt trauma from an impact. The VC is anexperimentally measured term that relates themaximum in the product of the instantaneousvelocity of tissue or chest wall compression withthe degree of compression to the level of resultinginjury on the abbreviated injury scale (AIS).8 The relationship between VC and BC hasbeen shown by Bir and Vian to allow estimationof the AIS level of injury 9 from the calculatedBC as follows: AIS = 1.33BC + 0.60.The BC is a term calculated from knownprojectile parameters (i.e., mass, diameter,velocity) and from target properties (i.e.,weight and thickness of tissue) that can beassumed for given scenarios. This allows usto graphically show how changing the size ofthe person impacted either increases ordecreases the risk of blunt trauma injury. Italso allows investigation of how changes inmass, diameter, and striking velocity of theprojectile may influence the risk of injury,either increasing or decreasing it. Bearing inmind that the relationship of BC to AIS wasdeveloped with non-compliant flat-nosedcylinders, it likely overestimates the severityof injury when the impactor is of a compliantdesign or the impacted person is wearingheavy or padded clothing.SELECTION OF PROJECTILE PARAMETERSTo be effective against persons using heavyclothing and padding as a countermeasure,and to be effective at temporarily incapacitatinga person, the projectile needs to hit hardand produce significant instantaneous pain.To have an acceptably low risk of injury, theimpactor should produce a predicted AIS levelinjury for an impact to the thorax less than 2,the threshold for moderate injury. An AISLevel 1 injury will not require medical treatment,and AIS Level 2 may require medicaltreatment and certainly will have a longerperiod for full reversal to pre-engagement levelof capability.Battelle non-lethal ballistic system demonstrationat an indoor range. Green earplugs are off hand shots at 35 and 65yards, and the orange ear plugs are offhand,sitting shots taken from 100 yards.Battelle non-lethal ballistic systemdemonstration. A 10 shot group wasfired outdoors from the prone positionat 115 yards (one of the 10 shots hitbelow the target).If we assume that a kinetic energy densityof 30 J/cm 2 is the maximal permissible, basedon risk of penetration beyond tearing of subcutaneouslayers of fat and muscle (i.e., fullprojectile penetration), then we must pick aprojectile cross-section that keeps the totalkinetic energy of the round below thresholdsfor other severe injury. Skull fracture fromimpact with steel drop weights typicallyoccurs over a range of 33 to 75 ft-lbs, 10,11 andfracture of the facial bones has been observedin the automotive crash test studies to occurfrom 30 to 40 ft-lbs for the mandible andmaxilla and 4 to 10 ft-lbs for the zygomaticarch. A kinetic energy threshold below thatfor fracture of the zygomatic arch would resultin an ineffective blunt impact. However, akinetic energy threshold of 30 ft-lbs, which isbelow the fracture thresholds of the otherbones listed, can result in an effective blunttrauma impact.This is consistent with the historic, nonlethalanimal effects studies of the late 1970’sin which the US Army Human EngineeringLaboratories and the Swedish ResearchInstitute correlated the kinetic energy of aprojectile to injury sustained by impacted surrogateanimals. Recommendations to limitkinetic energy for non-lethal projectiles weremade based on their experimental results. TheHuman Engineering Laboratories describedprojectiles with energies below 30 ft-lbs (40.5J) as having a low probability of causing aninjury. Projectiles with energies between 30and 90 ft-lbs (40.5 and 121.5 J) were considereddangerous, and projectiles with energiesabove 90 ft-lbs (141.5 J) were likely to cause“severe damage.” 12Eye injury also must be considered, but likefracture of the zygomatic arch, it occurs atenergies far below what is effective as a bluntimpact. Stewart concluded that eye penetrationby small spheres occurred at an impactenergy density of 6 J/cm 2 plus or minus 1.5J/cm 2 . 13 It is likely any blunt impact weaponwill produce severe eye injury. Exampleswhere paintballs impacted the unprotectedeye have been recorded in many case studies,and impacts to surrogate pig eyes with paintballsat 300 ft/sec (91 m/sec) have been shownto cause rupture and shattering of the eyeglobe. 14If the kinetic energy of the Battelle projectileis limited to a maximum of 30 ft-lbs (40.5J) and a kinetic energy density of 30 J/cm 2 atimpact, the calculated diameter of the projectileis 1.31 cm (0.516 inch). 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