THIS DOCUMENT CONTAINS PAGES, COPY NO./ OF COPIES. NON-PENETRATING IMPACT AS AN AGENT FOR PERSONNEL INCAPACITATION Prepared by: 31 January 1972 This report has been prepared by the a s a part of a Government contract. The views expres-. sed are those of -------- - lpersonnel and not neces- sarily those of the United States Government. TABLE OF CONTENTS Page Protocol Statement . . . . . . . . . . . . . . . . . . . . List of Figures and Tables . . . . . . . . . . . . . . . . Problem . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . I Discussion . . . . . . . . . . 2. . . . . . . . . . . . . 2 J. Potential Applications for Incapacitation . . . . . . 2 II. Physical Variables of Impact . . . . . . . . . . . 4 III. Physiological Considerations . . . . . . . . . . . 7 A. Impact as a Reaction . . . . . . . . . . . . . 7 B. Physical Basis for Biologic Effects 8 C. Biologic Effects 2. . . . . . . . . 9 D. Thresholds . . . . . . . . . . . . .. . . . . 11 E. Physiological Conclusions . . . . . . . . . . 21 IV. Other System Factors . . . . . . . . . . . . . . 23 A. Range . . . . . . . . . . . . . . . . . . . . 23 B. Covertness . . . . . . . . . . . . . 23 C. Duration of Incapaci2tation . . . . . . . . . . . Z3 D. Countermeasures . . . . . . . . . . . . . . 24 V. Equipment State of the Art . . . . . . . . . . . . 25 VI. Recommendations . . . . . . . . . . ... . . . . 28 References . . . . . . . . . . . . . . . . . . . . . . . 30 LIST OF FIGURES Pa@,,e Figure 1. Factors of the Reaction Between an Impacting Object and the Human Body . . . 7 Figure 2. Approximate Acceleration -- Injury Correla- tion of the Study by Higgins, et al . . . . 13 2 Figure 3. Suggested Approximate Thresholds for Impact Effects on the Head Under Laboratory Conditions . . . . . . . . . . . . . . . 14 LIST OF TABLES Table I Metric Units of the Fundamental Dynamic Factors of Impact . . . . . . . . . . . . 6 Table II Hypothetical Results of a Well-Develop2ed Concussion System Under Field Conditions 16 Table III Effects of Non-Penetra-tinc, Impacts on the In Trunk . . . . . . . . . . . . . . . . . la Table IV Estimated Durations of Incapacitation for Non-Repetitive Impacts . . . . . . . . . 24 Table V Effects of Soft Plast6ic Projectiles Designed to Cause Concussion . . . . . . . . . . Z6 NON-PENETRATING IMPACT AS AN- AGENT FOR PERSONNEL INCAPACITATION PROBLEM To evaluate, especially from the physiologic point of view, non-penetrating impact as an agent for personnel incapacitation. INTRODUCTION For the purposes of this report, a non-penetrating impact is considered to be a relatively high-6velocity collision between a.blunt object and the human body, excluding those collisions that break the skin. The results of non-penetrating impact are usually classed as blunt trauma in the medical literature. Healthy adult humans in the 45 to 90 kilogram weight range are assumed to be the subjects for incapacitation throughout this report. DISCUSSION I. Potential AT)T)Iications for Incapacitation Controlled impact can offer a number of advantages when compared to other proposed techniques for personnel incapacitation. Among the possible advan- tages are: Spectrum of incapacitation: pain, muscle spasm, breathlessness, un- consciousness, severe injury. Rapidity of incat)acitation: onset of action within a second. DirS!@@ with respect to person to be incapacitated. Controllabili@y: of time of onset and type of incapacitation. Safety- for the operator. SimglLcity: of techniquesatid equipment. Covertness: can be extremely quiet and unobtrusive. Most of the incapacitating biologic effects of impact are critically dependent 2 upon anatomic location, implying that an impact system would have to be aimed at a selected point on the subject's body by some means. Under field conditions, impact systems will probably not prove feasible for incapacitafing a group of subjects at one time although a system might be capable of incapa- citating a number of individuals in rapid succession. The aiming requirement also indicates that most systems would have to be controlled directly2 by an operator; any pre-set trap system would have to: (1) ensure that the subject will move precisely into a pre-determined position; or (2) be equipped with an elaborate automatic aiming subsystem. Incapacitation by impact alone will usually be brief unless the operator is willing to risk severe injury or death of the subject.. The rapid on--etof incapacitation by impact makes it a natural choice for the initial "9knockdown"' technique, to be followed immediately by application of a different method of maintaining control of the subject if prolonged incapacitation is desired. In the 'rolonged incapacitation case, the requirement for prompt application of p Z- a second technique may prove to be a limiting factor in the range of pro- jecta@le impact systems in that the operator(s) would have just afew seconds to approach the downed subject and apply the second technique. Within these limitations, a variety of impact systems could be developed for general or specific application. Exanples would be a hand-held "calibra- ted blackjack, " a relatively long-range projectile "stun gun" or a hijacker tr5ap installed on aircraft. The impact delivery system would be mechani- cally simple and reliable, using power from human muscle, springs, compressed gas, pyrotechnics, or other sources. Repeat action could be developed for use against multiple subjects. 3- II. Physical Variables of Impact Impact is collision, the forceful contact of two objects that have moved to- gether. In an elemel-itary sense, the basic factors of impact are simple: the mass and structural characteristics of each object and their relative velocity just before impact. In most practical situations, a detailed en- gineering analysis of an impact situation would require tha2t a large number of variables be considered and a complete description of the event would be extremely complex. A major complication in most impact analyses is that a number of important variables change rapidly and interdependently during a short time period. In a simple impact case, two objects approach' each other at a known velocity and in a known geometric relationship. Both objects start to be deformed 2 at the first moment of contact, and pressure and shear waves start to travel through both objects. The area of contact between the objects becomes larger as a result of deformation to "fit, " although pressure usually remains highest at the centerpoint of the contact area. Momentum is conserved and transferred between the objects. Kinetic energy is conserved, trar@sferred between objects, stored as potential ene2rgy, or dissipated as sound, frictional heat or disruption of one or both objects. Both objects accelerate; usually both ob ects are subject to combined linear and angular accelerations. If a sufficiently strong elastic component is present in the interaction, the objects will be forced apart and the area of contact will become smaller as one or both objects release potential elastic energy and start to restore their ori3ginal shape. -Impact is complete as soon as kinetic energy transfer is complete and the two objects are moving together as a unit (like aball of putty thrown so as to stick on a wall) or have broken contact to move independently again. Detailed analysis of the reaction described above would not be a simple -4- matter even with the simplest sort of homogeneous masses moving as "isolated systems" in the ideal physical sense, or with perfect billiard balls moving on a perfect billiard table. When one of the objects is as inhornogeneous, complex and irregular as the human body, the problem of impact defies detailed analysis except for minor extrapolations of empiri- cal data. Any systematic treatment of the human body i2n impact must consider the body as a number of masses connected in a variable geometry by supporting structures with rapidly varying mechanical characteristics. A blow to the head of a man reading a book is likely to have an effect quite different from the same blow delivered to the same man by an opponent in the boxing ring. Table I briefly defines fundamental dynamic units of impact factors, in the metric system. Non-metr2ic units commonly found in the impact literature are: 'latmospherel' of pressure equal to about 1. 01 - lOrdynes/crxi@ ; iic;ii of acceleration equal to about 980 cm/sec2; the English unit "pound" has been confusing because it may be used as a unit of mass or a unit of force. All of the factors noted in Table I are vector quantities except for mass and kinetic energy. 4This report will not deal specifically with the factors that determine the structural characteristics of colliding objects. The various moduli, strengths, viscosities and impedances that quantitatively define the compres- sibility, plasticity and elasticity of-structures in the human impact context have been reviewed by von Gierke. 5- TABLEI METRIC UNITS OF THE FUNDAMENTAL DYNAMIC FACTORS OF IMPACT Factor Definition Unit Eq'uivalent Mass Inertial characteristic of gram matter; proportional to "weight" in gravity field Velocity 2Rate of change of position cm/ sec Accelera- Rate of change of velocity cm/ sec 2 tion jolt 3 Rate of change of acceleration cm/ sec@ Momentum Product of mass and velocity; gm-cm/sec also, product of force and time Force Product of mass and accelera- dyne gm-cm/se 62 2 tion 3 3 Onset Rate of change of force; also, dyne/sec gm-cm/se C product of mass and jolt Pressure Force per unit area barye dyne/cm2 Kinetic Work capability due to motion; erg gm-cma/sec 2 energy 7 product of force and distance One Newton is 10 a dynes One joule is IC7 ergs. III. Physiological Considerations A. Impact as a Reaction The physical and biological consequences of impact are determined by the reaction between the impacting object and the human body. Figure 1 indi- cates a number of the factors and subfactors that enter into and modify the reaction. Primary impact factors are those related to the initial contact 2 The Reaction Anatomic location of primary impact; Relative velocity; Size of contact area; Direction of momentum vector relative to body axes 2 ImT)actiniz Objec I-iuman Body Mass; Mechanical characteristics of Size; the part struck; Shape; Size; Compressibility; Modifiers o2f the Reaction. Health; Plasticity; Interposed rigid shielding; Posture Elasticity; Interposed padding; of the part struck, Attachments to other struc- Support for body or parts of other parts tures; Muscle tone Orientation at moment of'impac 2 at moment of impact Surface characteristics Details of Body Acce eration Peak differential acceleration; Duration of acceleration; Shape of acceleration curve; Others 2 Primary Biologic Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Factors of Secondary Impact Secondary Biologic Effects Figure 1. Factors of the Reaction Between a* Impacting Object and the Human Body. 7 Including both linear md angular accelerations. 7- between an impacting object and the body. Secondary impact would be any subsequent impact events which might occur as a consequence of the first. Examples of secondary impact would be collisions between: (1) the same impacting mass anci a seconcl body part; (2) two bocly parts; or (3) some body part and a second object, such as a floor or wall. consideration of Figure 1 leads to the conclusion2 that many of the variables important to an impact problem a-:-e interrelated in a complex manner, and suggests that many factors carl be critical with regard to the biologic outcome of any given impact situation. B. Physical Basis for Biologic Effects. Most of the biologic effects of impact are due to mechanical deformations of body tissues. These deformations are the result of forces arising from differential ac2celeration of body parts. The forces may tend to compress, expand, bend, shear or twist the tissues. The force pattern is usually com'- plex and changes rapidly with time. Oscillations may travel to body areas. away from the site of impact in the form of compressional or shear waves, and oscillatory action could persist for a short time. Pre-impact momentum is conserved when the post-impact vector velocities of both the impact2ing object and the body are considered. These velocities also constitute part of the energy that is conserved through the impact event. Part of the kinetic energy of impact is converted to frictional heat from: (1) deformations of the impacting object and the body; and (2) contact with the air.and other surrounding materials. More of the kinetic energy may be absorbed in structural disruption or converted to potential energy or soun4d. The physic:tl effects of impact on living systems may be summarized as: (1) short term deformations; (2) longer term deformation including struc- tural disruptions; and (3) heating, usual minor. Redistribution of body fluids 8- and othcr effects only become significant when unidirectional accelerative forces persist longer than a second; these effects are beyond the scope of this report. C. BioloL7ic Effects. Most of the biologic effects that might be desired for temporary incapacita- tion of personnel are caused by the short-term deformations of tissue, especially those with rapid onset. A forceful push will not be a2s effective as a sharp blow for incapacitation purposes. The most dramatic transient effects of impact are those on nervous and mus- cular tissues. Appropriate rapid deformation of these "irritable" tissues can cause depolarization ("firing" of nerve cells, contraction of muscle fibers) and an alteration of the functional status of the tissues for some time after the blow. This is the mechanism of all the commonly experienced e2ffects that start with great rapidity following impact. Firing of nerve fibers in the skin and deeper. structures causes the immediate pain at the site of impact, as well as effects like the tingling pain that shoots down the forearm from a' blow on the "funny bone, " (the ulnar nerve at the elbow). Rapid compression of muscle tissue is presumed to be the cause of the fcharley horse, " a painfully persistent mass of spastic m2uscle resulting from a blow. The dis- play of lights "seen" by a person receiving a sub-concussive blow on the head is apparently caused by direct mechanical stimulation of the visual cortex of the brain; a similar display can be induced by experimental electrical stimu- lation of the visual cortex. Concussion, the sudden loss of consciousness immediately following a blow to the head, is presumed to be caused by short- term mechanical defor7mation.of the central nervous system. Electroenceph- alographic and animal studies indicate that concussion is due to functional changes in vital hindbrain centers. These same studies also indicate that certain'phases of the concussion-recovery sequence include suppression of basic reflex activitie.s, and other phases resemble natural deep sleep and. awakening. 4,5 Longer term effects of impact may include: (1) alteration in the per- eability of vasc,-ilar systems near the impact site; (Z) disruptions of m blood vessels; (3) dislocation and/or breakage of structures other than blood vessels. The permeability changes account for swelling, aside tic muscle, without discoloration. Breaks in blooci from lumps of2 spas vessels cause the subcutaneous hemorrhage of a simple contusion or bruise, as well as more serious losses of blood from the vascular sys- tem. Bones, cartilages and teeth are subject to dislocation by impact. Organs seriously injured by blunt trauma are usually classified as: skin and subcutaneous tissue; skeletal muscle; the complete skeleton including cartilage and teeth; heart and great vessels; the "hollow2 viscerati including the gastro-intestinal, biliary and lower urinary systems; the solid organs" including brain, liver, spleen and kidneys; and special organs such as lungs, eyes, genitalia and larynx. Impact can cause chain reactions of injuries such as a blow to the chest which fractures ribs in such a way that the rib fragments cut blood vessels and membranes covering the lungs. The latter injuries can lead to 2serious internal hemorrhage and potentially fatal lung collapse. Laceration of the liver or other solid organs can cause massive internal hemorrhage and perforation of any hollow viscus leads to a lif e- threatening peritonitis. Either of these latter injuries, along with bleeding inside the skull and any injury that prevents adequate respiration, will usually be fatal unless medical care, including major surgery, is av2ailable promptly. Frictional heat of impact may play a part in the biologic effects of high velocity low momentum impacts, such as a painful switch on the skin with a lightweight whip. Although the possible abrasive component of such a blow is difficult to evaluate, enough heat energy from the impact may be dissipated in the skin to cause some of the observed local effects. A whip mark can resemble a thermal burn in many w5ays, with painful red swelling and tendency to blister and peel. It is interesting to speculate that any rapid change in skin energy level tends to evoke a similar type of response, regardless of whether change is due to heat, cold, friction, electricity, ionizing radiation or high velocity impact. 10- D. Thresholds. For the purposes of the personnel incapacitation problem, the desired effects of impact would seem to be limited to: (1) concussion or other sudden decrement in level of consciousness; (Z) transient paralysis in- cluding apnea; and (3) pain or the threat of pain. The other effects noted in the previous section of this report either would @ot contribute to prompt incapacitation 2of the subject or would constitute a potentially serious in- jury to the subject. Some results of impact could be both ineffective and dangerous; a crippling or life-threatening wound might not necessarily be rapidly incapacitating unless it also had sufficient effect in at least one of the three categories noted above. The remainder of this report will assume that impact is to be arranged so as to maximize the three potentially incapacitating effe2cts and to minimize all of the other effects. Concussion without other damage could be a rapid and thorough type of incapacitation. Scientific attempts at evaluation of the factors and thres- holds of concussion started well back in the last century and continue to present. Evaluation techniques have ranged from analyses of accidents and sporting events to postmortem studies and carefully controlled impacts deliberately delivered to the heads o2f experimental animals. The results of all these investigations may be summarized as follows: 1. The detailed mechanism ar mechanisms leading to concussion remain a matter of debate. Some hypothetical mechanisms which have been advanced are as follows: (a) Local skull deformation with local pressure effects; (b) Increased overall intracranial pressure; (c) Differenti3al intracranial pressure; (d) Differential pressure across the foramen magnum; (e) Shear forces across the brain stem; (f) Linear acceleration of the whole head; differential motion (g) Angular head acceleration causing between brain and skull; (h) Cavitation; (i) Flexion-compression phenomena at the craniospinal junc- tion and, (j) Overstimulation of neck propriocept6rs. Several of these hypotheses have been more or less disproved, at least 2 in certain experimental circumstances, by later investigations. There is no generally accepted mecha nism or group of mechanisms for concussion. 2. There is general agreement: that alteration of function of struc- tures in the hind brain and brain stem is a of concussion; that a head free to move relative to the neck and shoulders is more subject to concussion than a firmly supported head; and that repeate2d concussive blows greatly increase the likelihood of serious injury or death. 3. Even with meticulous laboratory attempts to control all of the variables indicated in Figure 1, no investigator has been able to establish precise thresholds between non-concussion and concussion, or between concussion and more serious injuries. This failure is linked directly to the lack of understanding noted in paragraph 1 ab2ove. The careful work of Higgins, et al ;illustrates the difficulties involved in . . attempts to define a predictable relationship between impact and concussion. These investigators delivered calibrated, aimed impacts to the precisely oriented heads of twenty-five monkeys that had shaved scalps "potted" in plaster inside metal helmets. This ela0borate preparation brought under control many of the variables noted in Figure 1. Even under these special conditions, with skull deformation a virtual impossibility, the authors were unable to calculate impact characteristics that would reliably cause con- cussion without other serious injury. The concussive results were reported 12- not in terms of standardized impact "doses" but in terms of measured angular acceleration imparted to the head. The reported results of the study are approximately summarized in Ficure 2. A B 99,79 2 ? RAPIDLY FATAL (Percentage) 1070 INTRACRANIAL HEMORRHAGE 99% (Percenta2ge) 1010 9 9010 CONCUSSION (Percentage) laic 1. 0 1. 5 2. 0 2.5 3. 0 3.5 4. 0 4. 5 Angular Head Acceleration (106 radian.9 per seC2) Figure 2. Approximate Acceleration -- Injury Correlation of the Study by Higgins, et al. Figure 2 2indicates that under the extremely rigid artificial test conditions an acceleration level ".A" could have been preselected to yield rates smaller than 1% for serious injury or death in conjunction with "successful" con- cussion rates on the order of 25%. Acceleration level "Bl' co2uld have been expected to yield a concussion rate of 99% with a serious hemorrhage rate of about 50% and a rapid death rate still below 1%. The thresholds indicated by Figure 2 would have been even broader and more overlapping if the 163- investigators had been forced to relate the effects directly to some measurement of the delivered impact, rather than to the resultant head acceleration. A8mitting that their results give only the roughest approximations of thresholds, most other investigators have found that velocity of impact is as useful as any other single index in predicting effects on experi- mental animals when the2 mass of the impacting object, anatomic loca- tion and other factors are kept as constant as possible. The impacting object is commonly assumed to have a mass about equal to the weight of the head and neck of the experimental animal, or about 5 kilograms in the case of adult humans, and may be assumed to have the structural characteristics of a compact block of wood without sharp edges. Using these and other criteria, sug2gested approximate thresholds for impact effects on the head are shown in Figur.e 3. 99% ? RAPIDLY FATAL I,% . ? 9,9% 2 GROSS INTRACRANIAL HEMORRHAGE 99610 SKULL FRACTURE 1% 99% CONCUSSION 7 I% z 3 4 5 6 7 a 9 10 Impact Velocity (meters per secon@) Figure 3. Suggested Approximate Thresholds for Impact Effects on the Head Under Laboratory Conditions. 6, 7 14- The thresholds indicated by Figure 3 are approximately the same as those suggested for situations in which the head is rapidly decelerated by striking large objects such as the ground or structure of buildings or vehicles.7 Velocity of impact is the independent variable shown for Figure 3, al- though the stipulation that the impacting object has a mass on the order of 5 kilograms de2fines the abscissa in terms of momentum also. Ex- perienced investigators of the biologic effects of impact tend to agree that: (1) there is no single mechanical unit that provides an optimum measurement of the biologic "dose" of impact; and (2) velocity and/or momentum come closer than any other units to providing satisfactory correlations over a wide range of conditions. Kinetic energy correlations 2 break down at the low-mass end of the scale where high velocity objects penetrate the skull without causing concussion, and at high-mass end of the scale where biologic effects seem to be more in proportion to velocity than to energy. Acceleration or force values correlate to biologic effects only when the duration of action is taken into consideration. As indicated by Table I (page 6), integration of accel2eration or force with respect to time yields units similar to velocity or momentum. Detailed evaluation of mechanical impact events can be derived only from high-speed recording of some factor(s) in the displacement-velocity-acceleration spectrum from multiple sites around the head. Of the many possible single mechanical values, velocity seems to retain fairly uniform biologic significance over a wide 2range of conditions. Even momentum has a limited range: the impact effects of a slowly rolling automobile are quite different from the impact effects of a small lead pellet with momentum equal to that of the automobile. Figure 3, as imprecise as it is, must be considered as only the roughest guide to impact thresholds, and only under laboratory conditions. The experimental conditions under which these thresholds weremeasu0red usually included absolute control over the posture and orientation of the subject with respect to the impact. Such control implies previous incapacitation 15- physical res- of the subiect by some means, usually anesthesia and/or traints. Control of subject posturer orientation and other factors shown in Figure 1 (page 7) would be even more difficult under field conditions .. than it is in the laboratory. The net effect of such variability could only be to widen and increase the overlapping of the already broad t2hresholds shown in Figures 2 and 3. No numerical data from impact studies under actual or simulated field conditions are available. An impact incapacita- tion system might be developed that could yield results similar to those shown in Table II under selected field conditions. TABLE II HYPOTHETICAL RESULTS OF A WELL-DEVELOPED CONCUSSION SYSTEM-UNDER FIELD CONDITION2S Effects Impact Levels A B Concussion 5 0 alo:k 9 5 a/O:i: Non-Concussion 9 5 0,10:k 5 0 Olo:: F. 50/0+- Skull Fracture < 5 50 10 - 400/o > 5 07o Serious Hemorrhage < 5 olo 10 - 40(7o > 5 0 olo Rapid Death < 10/0 1 - 100/o > 1 0010 On the basis of presently available information, the hypothetical rates shown in Table II may even be overly optii-nistic with regard to the safety of blows to the head at concussive levels. It 3should be noted that Table II is concer- ned with-intracranial effects only; injuries to eyes and other facial struc- tures would be a separate consideration in anterior blows to the head. Non-penetrating impacts to the trunk offer no special advantages for The relative tolerance of human facial structures to impact has been repor- ted by Swearingen. 8 personnel incapacitation with the possible exception of the "solar plexus punch" to the epigastrium. This blow, familiar to participants in contact sports, causes the "breath to be knocked out" of the subject for periods ranging from a few seconds to as long as a minute. Characteristically, the subject remains relatively motionless in a doubled up position and is unable to breathe or speak until he recovers. The @xact mecha2nism by which both diaphragmatic and intercostal breathing is inhibited remains unknown; the "solar" or celiac plexus of nerves to the intestines may or may not be involved. The blow usually has much of the mass of a player behind it and is most effective when the subject is not tensed to receive the impact. A typical solar plexus blow might be characterized as landing be- tween the umbilicus and the xiphoid process, directed str2aight posteriorly or slightly headward, with an effective mass greater than ten kilograms and a velocity of several meters per second. Available reports mention no experimental work that would help to explain or quantitate the effective- ness of impacts delivered to the epigastrium. The equivalent of a solar plexus punch would probably be difficult to develop into a safe and effective technique for personnel incapacitation. A 2perfectly delivered impact that had been calculated to incapacitate a man tensed to receive the blow could prove fatal if the subject does not'tense in time. Errors in anatomic location and direction of impact would lead to decreasing effectiveness and increasing rates 6f serious injury and fatality. Properly directed but excessively powerful blows could kill by rupturing the aorta, diaphragm, stomach or other viscera. Blows 2slightly high could contuse the heart or cause lung collapse -from rib cartilage fragments. Lateral aiming errors could cause rupture of liver, spleen or kidney. A low blow could rupture a full bladder or other lower abdominal structure. Clemedson, et al have reviewed the relative tolerance of various body parts to blunt trauma, and come to the conclusion that liver, spleen and kidney are the organs most susceptible t5o severe injuries from flying missiles. 7 17- Table III sumn-iarizes the scanty information available on injury thres- holds for non-penetrating impacts on the trunk. It should be noted that the effects shown in Table III provide no guide to the effectiveness of a blow in causing rapid incapacitation. Even the lethal impacts shown in the table might cause no significant incapacitation for several minutes. The only rapidly incapacitating effects th at could be expe2cted from a non-fatal blow to the trunk would be pain and the solar plexus effects dis- cussed previously. Impacts on extremities are unlikely to cause'transient incapacitating effects other than pain. A blow that would pinch a peripheral nerve hard enough to cause a paralysis of the muscles served by that nerve is quite likely to destroy a section of the nerve. Long bones of the extremities can be broken by energ2etic direct-blows. These so called "billy club" fractures are more common in the shin and forearm where the bones are not heavily padded with soft tissue. Wartime British investigators conducted tests with experimental animals and e,;timated that direct blows by a metal rod with kinetic energies in the 1Z to 60 joule range should suffice to fracture the 9 human hume2rus, with a mean energy of Z7 joules. The same group estimated that three times as much energy would be required to break the stronger and better padded human femur. If these estimates are correct, blows with masses less than a kilogram and with fairly low energies (on the order of 5 joules) could probably break the human fibula, radius or ulna under some circumstances. Even so, certain fractures of the fibula and ot2her smaller bones may not be extremely painful, or otherwise incapacitating to the subject. "Safe" blows, therefore, could not be expected to cause much in the way of incapacitation. Transiently incapacitating pain can be generated by appropriate impact any- where on the body surface. Skin pain is caused by low mass, high velocity blows sach as those delivered by a willow switch. Blows from slightly heavier objec0ts can cause deeper pain if delivered to body areas where bones 18- TABLE III EFFECTS OF NON-PENETRATING IMPACTS ON THE TRUNK (After Clemedson, et al) 7 Impac t Moving Velocity Location Mass (kg) (.meter/sec. Effect Lateral chest 0. 18t Z4 2 local lung hemorrhage 0. 18t 36 lacerations from rib fragments 0. 18t 52 rapidly lethal 0. 36t 13 local lung hemorrhage 2 0. 36t Z7 lacerations from rib fragments 0. 36t 47 rapidly lethal Over liver 15. 5@ 2 minor liver damage 11 ti 15. 5* 4 t2hreshold of severe damage 15. 5* 6 10 rapidly lethal Whole body 70* 3 usually survive if it 70* 6 threshold of lethality it 11 70* 2 8 50% lethal 70* 9 near 100,7o lethal Clemedson implies that the data is applicable to the human trunk, although most of the experimental work was with animals. 7 t Missile comparable to a croquet ball. Pendulum weight of unspecified "solid" material. Whole bodies 6thrown, presumably laterally, against an unspecified large solid surface. 19- or cartilages have only a shallow covering of soft tissues. This pain arises from the sensitive periosteal, or perichondreal, membranes cover- ing bones and cartilages. The relatively hard material underlying perios- teum makes the membrane susceptible to a pinching action from brisk impact with a hard object. Periosteum is usually shallow in the following body areas: skull, clavicles, extremity joi2nts, shins, backs of hands and tops of feet. Certain body areas deserve special comment with regard to impact sensi- tivity. The eyes and the laryngeal area are extremely sensitive to pain and impact, but blows that would be inconsequential elsewhere on the body could cause severe injuries in these two areas. The testicles are also extraordinarily sensitive to pain from impact, but are much less likely to b2e permanently damaged by a blow. Testicular pain is particularly suitable for incapacitation in that it is intense, prolonged and tends to keep the subject in a doubled up position. The fact that testicular function is not permanently impaired by intensely painful impact is indicated by the rarity 10 of major testicular injury in contact sports where rigi2d shielding is not worn. Peripheral nerves are pain sensitive organs b ut usually are too deeply buried in other soft tissues to be directly effected by non-penetrating impact; the only common exception is the "funny bone, " actually the ulnar nerve at the elbow. As previously noted, impact to muscle can cause painfully persistent muscle spasm of the "charley horse" variety. Although scienti- fic proof is lacking, c2urrent medical opinion regards the painfully "paralyzed" upper extremity from a "rabbit punch" or "karate chop" to the lateral base of the neck as voluntary immobilization of the extremity due to the painful spasm of shoulder muscles, rather than any direct effect on the deeply buried motor nerves to the extremity. Large volumes of muscles could be struck with relative safety as follows: buttock, thigh, calf and any aspect 0 of the shoulder except the front and tip where bones are shallow. 20- E. Physiolorical Conclusions Pain is the most easily obtained mode of."safe" incapacitation by non- penetrating impact. High velocity, low mass impacts anywhere on the skin surface can cause transient stinging skin pain with little risk of serious injury to the subject. Slightly heavier blows directed to bony areas can cause severe periosteal pain. Still heavier blows to large muscle masses can cause painfu2l muscle spasm, and probably some de- gree of paralysis of the body part involved. The most incapacitating, relatively safe pain is probably that from testicular impact, with no comparable point of aim available in the female subject. The painful apnea of a heavy low velocity blow to the epigastrium remains a medical enigma. The physiologic mechanism that stops all respiration is unknown and there is no quantitative information available t2o estimate the effectiveness of blows with varying mechanical characteristics. In general, blunt trauma to the abdomen leads to poorly predictable and some- times fatal results. A highly developed system to incapacitate by "solar plexus punch" impact could possibly prove to be about 500/o effective with only 20'7o serious injury and 501o mortality under favorable field conditions. Effectiveness could prob2ably be raised, but only at the expense of in- creased morbidity and mortality. These figures are strictly speculative and the actual values of any system would have to be proved in field trials. True cerebral concussion has been the subject of much medical, engineering and interdisciplinary study. In spite of all this effort, many aspects of the concussion problem continue to defy detailed analysis. The fact remains that the most able in2vestigators, controlling a large number of variables, and using corr,71etely incapacitated experimental animals under carefully defined. laboratory conditions, have been unable to define the head impact that will reliably cause concussion with only a low risk of permanent brain damage. This result will certainly not be achieved under field conditions until it has been achieved in the laboratory. At the present state of knowledge, 7 21- it may be hypothesized that a concussion system 95'7o effective under favorable field conditions would cause permanent brain damage in about 5017/o and sudden death in about 107a of cases. Lesser hazard could pro- bably be achieved at the expense of effectiveness. The blow to the head might be put in a more favorable light if significant incapacitation could be proved for sub-concussive impacts. Most inves- 2 tigators mentioned above defined concussion in strict terms to mean a deep level of unconsicousness, often with the loss of certain basic reflexes. A smaller decrease in the level of consciousness might well suffice in certain personnel incapacitation situations. Available information does not allow any worthwhile estimates of the mechanical characteristics, effec- tiveness or hazard of such impacts. Impacts to the'face and anterior neck sh7ould not be used in most incapacita- tion situations. The likelihood of permanent injury to eyes, other facial structures or larynx would be high, and the area offers no special modes of incapacitation other than blindness which is likely to be permanent. 22- IV. Other System Factors A. Rai-ig All impact effects aside from skin pain will be initially dependent upon point of aim and the subject's,orientation and posture. Such dependence is likely to restrict the range of impact systems severely, at least for systems that are reasonably reliable and offer some degree of safety for the subject under a variety of field conditions. A perfectl2y aimed low velocity missile will not hit properly if the subject turns or moves between the time of firing and the time of impact. At best, systems with ranges longer than arm's reach would seem to be useful only in situations where the subject is: (1) relatively motionless in the first place; and (2) unaware of the action being taken against him. Direct rhanual control, so that direc- tion and velocity can be corr2ected continuously up to the moment of impact,. would seem to be the only reasonably safe way to deliver a heavy blow to a moving and/or wary subject. At the present state of knowledge, systems causing skin pain are likely to be the only safe and effective ones having ranges greater than a few meters. B. Covertness Properly designed impact incapacitation systems should be relatively quiet and unobtrusive in operation. T0he subject's response is likely to be noisy except in cases where a concussive blow, the solar plexus punch or testicu- lar impact had been used. C. Duration of Incapacitation Estimated durations of incapacitation by non-penetrating impacts are shown in Table IV. 23- TABLEIV ESTIMATED--DURATIONS OF INCAPACITATION FOR NON-REPETITIVE: LMP.AC.TS Mode of Estimated Incapacitation Duration Pain: Skin less than 5 seconds Periosteal 2 less than 10 seconds Testicular 5 secconds to several mins. Muscle spasm 5 seconds to several mins. Solar Plexus less than 1 minute Concussion 10 seconds to several hrs. Light impacts, such as those causing skin or periosteal pain, can be safely 2 repeated several times to extend the time of incapacitation. D. Countermeasures Appropriate armor and/or padding could be an effective countermeasure to an impact incapacitation system. Mod..grn football helmets offer excellent pro- tection against blows that would have devastating effects on a bare head. Rigid cup-like protectors could nullify the effectiveness of impacts to the genital region. 8 24- V. Equipment State of the Art A number of projectile systems have been developed for the purpose of per- sonnel incapacitation without lethality, if not without serious injury. II- 13 Other non-penetrating impact systems have been proposed. 14, 15 Almost all of these actual and proposed systems have been based on inadequate design criteria with regard to "safe" incapacitating2 impacts because, as explained in the previous section of this report, mechanical design criteria do not yet exist for most of the desired biologic effects. With their masses in the I to 5 gram range and velocities over 100 meters per second, the Speer .38 and .45 caliber projectiles and the Wyle .38 caliber projectile would clearly be unsuitable from the biologic as we 11 as the ballistic point of view. 11 2The test data on the second generation Scimitar flechette indi- cate ballistic success and biologic failure in that virtually 10070 of test missiles at least partially penetrated the biologic targets. 12 The results of rather elaborate effectiveness tests on soft plastic projectiles' hitting the heads of experimental monkeys and baboons are shown by Table V. Test series II and III were conducted using "improved" techniques modified as 2 indicated by experience. The investigators regarded the results of the third series as good enough to warrant a basically favorable report on the approach. The results shown in Tabel V were not achieved under simulated field con- ditions but under rigid laboratory control, including prior complete incapa citation of each experimental animal for positioning purposes. Obviously the morbidity and mortality rates experienced during these three seri2es of tests would not be acceptable for incapacitation of human subjects. The difficulty of developing a device that will reliably cause concussion, regardless of other constraints, is illustrated by the special device for "knocking" cattle before bleeding in slaughter houses. This pistol-like de- vice is hand held between the ears of the animal, aimed and fired. The blunt striker causes a depressed skull fracture, gross brain damage and,9 25- TABLE V. EFFECTS OF SOFT PLASTIC PROJECTILES DESIGNED TO CAUSE CONCUSSION Test Series I II III Number of animals Incapacitated * (percentage) Not Incapacitated (percentage) Skull fracture (percentage) Rapidly lethal (percentage) for 5 seconds or longer 2 hopefully, concussion. In the small test series reported, skull fracture and brain damage were achieved in all cases but 167o of the animals continued to struggle after the first "knock" and required a second shot. 16 Available information suggests that the only sophisticated device that has been proved to satisfy in any degree the objective of this report is the Reming- ton "Stinger" 12 gauge shotgun load. This cartridge fires about 2 350 polyethy- lene spheroids about 3 millimeters in diameter and weighing about 0. 02 gram each from a standard shotgun at unstated velocity. The manufacturer recom- mends that the load be aimed at the ground about a meter in front of the subject so as to ricochet and strike the subject below the knee only. Reported test results indicate: (1) gross tissue destruction at ranges of 3 meters and less; (2) brief inc2apacitation by pain without serious injury at ranges between 5 and 10 meters; (3) no effect at ranges greater than 15 meters; and 4) appropr ate clothing would be an effective countermeasure at all ranges greater than 5 meters. Some ancient weapons could satisfy the requirements for "safe" incapacitation by pain if they are properly used. The police baton is a case in point. Standard 4 26- batons in the United States are hickory cylinders about 3 centimeters in diameter and 65 to 92 centimeters long, weighing 380 to 525 grams. 17 Wielded at peak velocities of 5 to 10 meters per second, these instruments could clearly be lethal if used indiscriminately. Recommended police baton procedure is to threaten, push, or strike the subject below the knee. Blows 18 to the head are to be avoided if at all possible. Broken bones are a definite possibility with heavy blows from a baton. Handheld instruments lighter than the police baton might prove useful in some circumstances where incapacitation could be prolonged by repeated impacts causing skin and/or periosteal pain. Instruments similar to a light, flexible walking stick or a long riding crop could be designed so as to cause no permanent da1mage if the face and anterior neck are avoided. Such an old- fashioned technique could be called incapacitation by flogging. A carefully designed variation of brass knuckles could cause periosteal pain with an openhanded slap at a subject's scalp or other bony area, and at the same time be ready to add weight to a fist blow if required. 27- VI. Recommendations 1. In the light of present linowledge, the outlook for non-penetrating impact as a reliable agent for incapacitation without permanent damage is poor for all impact effects except pain. It is doubtful that laboratory results in the next few years will justify a more favorable view of the possibilities of a general purpose system delivering heavy blows to the body. 2 2. Consider the hypothetically possible results of a general purpose con- cussion system shown in Table II, page 16. If similar results are acceptable as a goal, proceed with concussion system development anil field testing. If such results are unacceptable, abandon development of concussion systems until laboratory demonstration of results better than those shown in Table II. 3. Insist on some documentation of biologic ef2fectiveness and hazards of any proposed impact incapacitation technique, other than those incapacitating by superficial pain, before starting detailed hardware development programs. 4. Heavy impacts might be useful in special circumstances where the subject can be expected to be relatively still in a predetermined location and posture. For example, the space behind the pilots' seats in an airliner could be partial2ly covered by a large piston-like movable panel in the overhead or sidewall trim. If a hijacker moved into the proper position, a pilot could trigger. the 10 kilogram or heavier piston to move down or out and hit the subject at about 3 meters per second. The effects of such an impact should give the pilots a few seconds in which to apply restraints or otherwise con- tinue incapacitation of the subject, and likelihood of permanent injury to th4e subject from the primary impact or any secondary impacts should be small. Similar'methodology might be appropriate in other special situations where the system can be closely controlled and rapidly followed up by competent operators. 5. Projectile systems are and will probably continue to be of Iii-nitcd utility if safety of the subject is of any concern. Like the Remington Stinger load$ they will probably remain constrained by a minimum safe range and a maximum effective range that are not too far apart. 6. A device with a range greater than that of the human knee could prove useful in incapacitating males by testicular impact. Blows deliv2ered up- ward between the legs offer the possibility of highly effective incapacita- tion with a relatively wide margin of safety, although little scientific information is available on this technique. 7. Lightweight handheld instruments on the order of riding crops could be used in some circumstances to incapacitate by repeated applications of superficial pain. Carefully designed brass knuckles could also prove use- f ul. 2 29- REFERENCES 1. von Gierke, H. E. , "Response of the Body to Mechanical Forces, in Lectures in Aerospace Medicine .j Sixth Series, USAF School of Aerospace Medicine, Brooks Air Force Base, Texas, 1967, pp 3Z6-344. (UNCL) 2. von Gierke, H. 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