AM 65-12

SURVIVAL OF HIGH-VELOCITY

FREE-FALLS IN WATER

April 1965

OFFICE OF AVIATION MEDICINE

FEDERAL A VIA TION AGENCY

zatoi 020 -s o a .

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AM 65-12

SURVIVAL OF HIGH-VELOCITYFREE-FALLS IN WATER

Richard G. Snyder, Ph.D.

Approved by Released by

STANLEY R. MOHLER, M.D. M. S. WHITE, M.D.DIRECTOR, CARI FEDERAL AIR SURGEON

April 1965

FEDERAL AVIATION AGENCY

Office of Aviation Medicine

Civil Aeromedical Research Institute

Oklahoma City, Oklahoma

ACKNOWLEDGMENTS

The author gratefully wishes to acknowledge the generous assistanceprovided in this study by Joseph W. Young, A.M., and Clyde Snow, M.S.,Physical Anthropology Laboratory, CARI; John C. Earley, Chief, DynamicsEngineering Laboratory, CARI; Robert Dille, M.D., Regional Flight Sur-geon, Western Region, FAA; Jim Scow, M.D., Langley Research Center,National Aeronautics and Space Administration; John Ice, Technical Editor,Acceleration Program, CARI; Laura Newell, Ph.D., Dept. of Anthropology,University of Washington; and Capt. T. F. Parnow, California HighwayPatrol. In addition, this study would not have been possible without theextensive cooperation and assistance provided by individual physicians,federal, state, and local police agencies, witnesses, and the subjects themselves.

SURVIVAL OF HIGH-VELOCITY FREE-FALLS IN WATER

I. Introduction. to answer and dependent upon a number of inter-Protection and survival of the aviation popu- related and variable conditions. This study is

lation involves many interrelated facets of vary- one attempt to initially define some of these vari-ing interest to the design engineer, human- ables and find means of predicting human sur-factors specialist, and aeromedical scientist. vival in water impact.Progress in most of these -areas eventually is Human falls into water from great heightsdependent upon basic knowledge of human capa- have been recorded throughout history. Thesebilities and tolerances to the varied, and often have not always been successful, and perhaps thehostile, environments imposed by flight. One mythical fall of Icarus into the sea as he at-such area is that of human tolerances to impact tempted to escape from Crete with his father,forces, in which considerable work has been done Daedalus, was the first. Although early medicalinvolving the horizontal component at subin- references, such as Gould and Pyle's Anomaliesjurious levels. Relatively little is known, how- and Curiosities of Medicine of 1901,"1 provideever, concerning human-tissue responses to ver- several cases of "Remarkable falls" into water,tical forces, partially at the higher sublethal including that of a sailor who survived a falllevels. of 120 feet from the topgallant of an East India

High vertical forces are most often encountered merchant vessel, early falls do not compare withduring crash landings,', 2 evaculation from the the much greater heights man commonly fallsaircraft after it has stopped, 3, 4 or during ex- from today. Man himself has provided thetreme turbulence in flight. 2, 6, 1 Such forces are means in constructing tall bridges, towers, air-often unintentionally encountered by parachutists craft, and other suitable structures from whichwho are unfortunate enough to be dependent upon he daily jumps, falls, or is pushed. These inci-ailing equipment. They may also be anticipated dents may provide valid scientific informationin VTOL-type-aircraft launch and landing ac- that is unobtainable through laboratory experi-cidents. mentation because of the obvious limits human

Quite often the material impacted in high- voluntary subjects can be exposed to in impact.

velocity vertical impact consists of a water sur- On the other hand, free-fall cases may presentinvoluntary experiments in which the subject

face; thus, both the general incidence and pe-

culiar characteristics of water survival merit greatly exceeds these laboratory limits. In se-

study in greater detail. One immediate applica- lected cases, in which investigation results in

tion for such knowledge is in the impact survival documentation of the major variables, certain

of astronauts exposed to extremely abrupt de- conclusions are valid. As this study progresses

celerations upon water impact due to retro- and sufficient cases occur to reproduce and rein-

braking equipment failure. In re-entry a drogue force the evidence to date, definite patterns oftrauma should become evident, as well as discretefailure may result in a splash-down of 130 ft/ indications of the major variables influencing

sec (88.6 mph) or more. Impacts in water human survival of extreme impact forces.of 25,000 G/sec, with a peak of 60 G, M.cr or There is apparently a wide, overlapping, and100 G land impacts ed for the Mercury capsule variable area between human limits of minimalhave been predicted. In this regard it is im- injury as found in the laboratory and the ex-perative to know the design limitations of the treme limits of survival. Although this has beenhuman body to such forces before a judgment explored to date to only a limited extent, knowl-can be made as to "how great an impact is sur- edge of the variables and problems involvedvivable." This is far from a simple question should be of considerable application to increased

protection and survival of the individual involved Narrows Bridge between Staten Island andin abrupt deceleration occurences. Brooklyn are 690 feet over New York Harbor,

and other bridges (Glen Canyon Dam Bridge)II. Materials and Method. are even higher, providing constant exposure to

During the past 3 years, cases have been care- the hazards of free-falls,' for such workers. (Al-fully documented of voluntary and involuntary though two cases of parachute failures were ob-free-fall ,with particular emphasis upon survival, tained, including one involving an ejection from12, 13 14, 15 Of some 18,000 cases during this time 15,000 feet over the Pacific Ocean and a second,involving survived free-falls, and 7,000 fatal in- a female sky-diver falling 2,550 feet into acidents of which we have knowledge, 200 sur- pond, these are not included here since aerody-vived cases to date have been selected for more namic drag could not be accurately determinedintensive investigation. Forty-four cases of hu- in either case.) In each case, measurement of theman impaction with water surfaces in unimpeded distance of the fall allowed calculation of thefree-falls of 55 feet (velocity of 52 ft/sec, or velocity. Note that standard velocity in each35.5 mph), or higher, are included. In each case has been corrected for air drag at sea levelcase, a site investigation was made, actual meas- (standard pressure, assumed body terminal ve-urement made of the distance of the fall, inter- locity of 120 mph).views conducted with the subject and witnesses, The calculated values used in this study arephotographs and police reports obtained, and the thus lower, but more realistic than that providedcomplete medical history forwarded, including by the standard formula (V = V/ 2gS) alone,copies of any x-rays. From these data, calcu- since preliminary tests and mathematical calcu-lations of free-fall velocity and direction of lations have shown that clothing such as jacketsforces were obtained from analysis of the medi- or skirts do provide additional drag. Correc-cal and biophysical evidence. tions by Earley 16 are based upon Cotner's17

This population represents a highly select closed-form solution for velocity at impact forgroup of individuals in that they had to have sur- fall cases where body position ;and clothing wasvived an extreme impact of over 50 ft/sec on a observed to be constant. A mean body build ofwater surface. Additionally, except for four 4.7 CDS (drag coefficient X body surface area)cases occurring prior to 1962, they represent a was utilized.high proportion (96%) of all known survivals In Figure 3, velocity is plotted against theunder these specific conditions during the past 3 variables of age, sex, and body orientation (di-years. It must be emphasized that the total rection of force) at impact. There were 34 malespopulation that fell under these conditions is and 10 females in this study. Although age ex-not considered here since fatal cases are not in- tremes of 7 to 80 years were involved, 69% ofcluded. Therefore, the actual incidence of sur- the subjects were between ages 20 and 40, andvival is not shown but rather a discrete analysis all of those surviving impacts greater than 100of the micropopulation that did survive. The ft/sec were between 7 and 26 years of 'age.following data must be used with this limitation Seven, or 70%, of the females surviving thesein mind. extreme impacts were between ages 20 and 29.

There is thus some correlation with age, with aIII. Results. greater number of younger individuals, both

The 44 falls investigated occurred in 17 differ- male and female, having survived at the higherent states (Figure 1) with 9 in Washington, 7 in impact velocities. This probably reflects physicalMassachusetts, and 5 each in California -and condition to some extent, although a subjectiveNew York. All but 4 cases involved falls from assessment was not available; however, this doesbridges, with 24 of these being suicide attempts not present the total incidence of survival, which(Figure 2). would show whether this could be due to greater

Bridge construction and painting accounts for exposure at higher velocities.a high incidence of falls from great heights into Survival occurred in various body positionswater. Towers of the Golden Gate Bridge, for up to 87 ft/sec lateral (-Gy), 88 ft/sec proneexample, jut 746 feet over the San Francisco (-Gx), 93 ft/sec supine (+Gx), and 97 ft/secBay, while the towers of the New Verrazano- head-first (-Gz). At all levels of velocity (dis-

2

tance of fall from 46 feet) above 50 ft/sec, how- first lumbar vertebra), shock, and hemorrhagingever, the feet-first ( +Gz) impacts had a sig- of the lung.nificantly higher survival incidence. Aside from Besides the high incidence of compressionthe two parachute failures, which are assumed fractures in this impact position bilateral mid-to be terminal-velocity impacts, four other cases shaft fractures to the tibia and fibia, femur, orof survival occurred in the feet-first body ori- humerus occurred. In one case, a comminutedentation [at 100, 102, 111, and 116 ft/sec (133 fracture of the scapula and distal clavicle oc-ft/sec standard velocity)]. curred when the individual landed with one arm

The upper survival limits of human tolerance down, forming a fulcrum against the impactto impact velocity in water are evidently close to force. Fracture patterns in water are distinctly100 ft/sec (68.2 mph) corrected velocity, or the different from those that occur on concrete,equivalent of a 186-foot free-fall. As is illus- steel, or soil surfaces since not one case of foottrated in Figure 3, there is a fairly constant or ankle injury was reported for the former,survival frequency distribution up to 100 ft/sec, while in the latter a high frequency of frac-but survival incidence at higher levels drops off tured ankles in feet-first impacts has been found.abruptly and includes younger individuals only. The midshaft fractures also differ from the pat-Regrouping these cases of survival by arbitrary tern most typical of impacting nonwater sur-class intervals, as in Figure 4, shows this pattern faces. This probably occurs as a function ofwith an abrupt peak at a 100-ft/sec impact ye- pressure changes as the body angles into thelocity. Twenty-five percent of these individuals water, literally snapping the long bones unlesssurvived extreme impact in water at from 90 to the legs are kept together. Extensive internal100 ft/sec, while only 4.9% survived a greater trauma occurred in only five individuals (14.4%),impact at any level. but the lung, kidney, spleen, liver and bladder

Previous studies involving human impacts on appeared most susceptible to injury. One case,other surfaces, such as concrete, steel, and soil, although fatal 48 hours later, showed uponhave demonstrated no clear-cut correlation be- autopsy a ruptured liver, spleen, and intercostaltween the distance of fall (and impact velocity) artery. Often internal trauma of a more minorand degree of resulting trauma. The 44 cases of nature, such as tearing of organ membranes,water impact studied in this investigation also may remain undiagnosed, as is indicated byshow no correlation of velocity (distance) with numerous autopies in our files. Other studiesinjury. In one case, for example, serious injuries of human water impacts have also confirmed theoccurred from a 55-foot free-fall (velocity 58 ft/ high incidence of external skin lesions, "I andsec, or 39.5 mph), while in others of much higher noted the extensive injury to internal organs invelocity, minimal contusions or no injuries were survivable impact. 19 20, 21, 22

reported. No clinical injuries were reported in Impacts in the five other positions identifiedone case at 95 ft/sec (64.8 mph) impact and an- are reported but, since only one to three occur-other 178-foot feet-first fall impacting at 97- ences were obtained for each, the results mustft/sec (or 66.1 mph) velocity, be interpreted with caution. It does appear that

Patterns of injury were found to vary with internal trauma is significantly more frequent inthe direction of force or body orientation. This any position of impact other than feet-first.is shown in Figure 5, in which gross injuries Only 1 (head-first) out of 10 cases of impact inwere summed up into four ar•bitrary classifica- another position failed to result in internal in-tions-no injury, external tissue injury, skeletal jury, with renal hematoma being most common.injury, and injury to internal organs, tissues, and Two individuals striking buttocks first, one atsystems. Of 34 cases of feet-first (+ G,) impact, near terminal velocity, were both injured, re-which was the most commonly survived body ceiving similar injuries as those impacting feet-orientation, 11, or 32.3%, had no associated first, except for one who landed on his buttockstrauma clinically reported. In all other body and right side, thus receiving a fractured secondorientations, some injury occurred. The most lumbar vertebra transverse process and fracturetypical injury in feet-first impact involved con- of 10 ribs.tusions to thighs and buttocks, compression frac- Other data were secured in investigation oftures (particularly to the twelfth thoracic and each case, such as clothing worn, physical data,

3

meteorological conditions (depth of water, wind, elementary, it is a basic factor in water-impactcurrent, and tide conditions), and whether the survival.subject had been intoxicated, under the sedation Velocity at impact is used in this study toof drugs, or had a psychiatric history. In three indicate magnitude of force because it can becases, jump boots and other protective clothing accurately calculated in unimpeded free-falls,such as helmets, a water skier's float, or heavy providing a valid basis of relative fall severity.clothing may have contributed to preventing fur- Unlike falls onto hard surfaces such as concrete,ther injuries. Several individuals, however, care- however, the deformation characteristics of eachfully shed clothing prior to jumping. Although impact cannot be precisely determined since theit is felt that knowledge of the possible influence displacement is not known. Thus, time duration,of drugs, alcohol, or certain psychiatric condi- a most important factor in deceleration calcula-tions would be useful for comparisons in their tions, cannnot be accurately determined. Inrelationship to impact survival, the clinical data general, the time duration, and rate of changeare not specific enough for a valid comparison, of velocity, in water impacts is of much longerAlthough 14 individuals were noted to be al- duration than in impacts on solid surfaces.coholics, intoxicated, or to have been drinking Stopping distance will vary with the body or-prior to impact, in no case was a blood-alcohol ientation at impact, being much greater in feet-determination made that would allow more ob- or head-first impacts, and less, because of thejective comparison with presumably sober greater surface area, in lateral or transverse im-jumpers. In addition, 15 individuals, including pacts. Evidence does seem to indicate, however,some of the intoxicated ones, were also diagnosed that even from great heights velocity is rapidlyto have various mental abnormalities, 'the most, lost in water. 23, 24, 25 Experiments by Neuritercommon of which was schizophrenia. Although and Trey, for example, showed that in head-previous work 3 has suggested a relationship first dives into water from 238 cm (7'9") dum-between relaxed muscle tonus, as may occur in mies (mass 3.38 kg, specific gravity 1.08) hadthe intoxicated individual, and impact survival, lost 71% of their velocity by a depth of only 16the data obtained to date in water impacts are 16 cm (6.3"). 21

not felt to be adequate for inclusion. We intend to conduct further experiments and.Discussion. try to duplicate with instrumented subjects spe-

IV. Dscific conditions of free-fall in order to caluateWhile it has generally been considered that the time duration sand estimate G forces acting upon

wider the distribution of force over the body's the body. Preliminary calculations involvingsurface, the less the unit force, and thus the stagnation theory indicate that G forces upongreater distribution of energy (and survival ca- the body in water impact are five to seven timespability), this one factor by itself is somewhat greater in the prone (+Gx), supine (-Gx), ormisleading, particularly in regard to water im- lateral (±+G,) body orientation than head-firstpact. For example, practically everyone has (-Gz) or feet-first (+Gz) impacts. Mathe-experienced the "belly flopper," which is a dis- matical estimates by Earley 17 predict a magni-tribution of force over a wide surface area. Yet tude of force in feet or head-first impacts of ap-a clean dive or jump into water, representing a proximately 3.5 G at 20 ft/sec, compared to 18.6much smaller surface area and thus greater con- G in a flat configuration, 6.0 G versus 40 G atcentration of force, leaves little or no sting. The 30 ft/sec, 16 G compared to 112 G at. 50 ft/sec,difference, of course, is in the deformation char- and 43 G compared to 300 G at 80 ft/sec. If cor-acteristics of the water, and thus the distance rect, these approximate theoretical values sug-and time duration of deceleration. In the "belly gest a major reason why incidence of water-flopper," the time duration of impact is short, impact survival is so much greater in head- orand "braking action" due to the greater surface feet-first configurations. For the same distancearea results in shorter stopping distance, while of fall and same velocity, an individual mayin the clean dive the time duration of impact is thus protect himself by roughly 50% to 70%greater since there is less braking action due to from G forces acting on the body by presentingdecreased body surface area and greater depth a minimal surface area at impaction.penetration. While this may seem obvious and It should also be noted that while plots of

4

these theoretical values provide two divergent moving water. Perhaps the champion voluntarylines, in most cases (except for trained profes- jumper was Ray Woods, who jumped all oversional divers), the minimum line will show sev- the place in the mid-thirties, jumping 165 feeteral peaks after initial impact and may even from the Aurora Bridge in Seattle in 1935 andrapidly approach the secondary maximum levels surviving, with back injuries that ended his car-due to change of body orientation after initial reer, a fantastic dive of 186 feet from the Sanimpact. Francisco-Oakland Bay Bridge in 1937. A third

In water impacts, factors not usually associ- diver, during opening ceremonies of the Mt.ated with ther types of surfaces may play an Hope Bridge at Portsmouth, Rhode Island, inimportant role in determining survival. For ex- 1927, jumped 154 feet, wearing a padded suitample, the surface of the water may be smooth and helmet.and horizontal to the falling body or through In various parts of the world other high diverswaves and throughs form a surface angle nearly frequently dive great distances. In Mexico, forperpendicular and thus parallel to the body. example, professionals regularly dive distances ofEven in inland waters, waves may be a factor. 100 and 135 feet from a Pacific Ocean cliff atVelocity of the current, while a relatively minor Acapulco, Mexico. One of these has dived thisfactor at impact, is immediately important to distance approximately 26,000 time in 25 years ofsurvival. Meteorological conditions thus are diving. A study by Schneider, Papo, and Al-often of more importance to water impacts than verez 27 notes that no fatalities have occurred,other impacted surfaces less subject to variation, except to an American college diver who at-Additional forces acting in a water impact may tempted to duplicate this feat. Various injuriesinvolve such factors as friction, tumbling, water have been incurred, however, including fracturesupslope, resultant forces, and even shear due to of the metacarpals or radius and ulna, caused bycurrent. the extremities striking the head on impact with

While most bridge-jumpers are attempting to the water. Compression fractures were found in

commit suicide, and others fall accidentally, it four of six divers examined, involving the fifth

should be noted that there are two further groups thoracic vertebra in three cases, the sixth thoracic

of voluntary jumpers, both gamblers *in a sense. vertebra in two cases, and the second, third,The first of these are those, usually young males, fourth, and seventh thoracic vertebra. Alongwho jump on a -bet. Strangely enough, we have with well-developed neck muscles, their success is

only one case of a known "bettor" who has been attributed to either extending the arms or lockingkilled. But frustratingly enough, there are sel- the fingers so as to "strike so that their necksdom records of such cases, and the individuals are slightly hyperextended and the point of im-usually, presumably clutching their winnings, pact is at the bregma." 27 In the "hands-apart"elude official searchers. In recent cases of this impact the force was mainly taken on the head,nature, a Rhode Island youth leaped 60 feet from while with the hands locked cavitation resulteda bridge while his companion stood by yelling in less force on the head.encouragement, and another jumped 135 feet The leader of this group of divers noted thatand was last seen swimming to a pier. In Ohio, in diving from less than 30 feet a diver shoulda 17-year-old boy jumped 65 feet, and in New remain relaxed; over 30 feet he "must be as rigidYork a 32-year-old man jumped 107-feet-for as possible to take up the blow." 27 Such stuntthe third time-from a bridge on which 67 other dives do emphasize that a water impact can bejumpers have been killed, repeatedly made at velocities up to 86 ft/sec

There have also been several men who make with no or minimal injury if proper body ori-a somewhat precarious living as stunt-jumpers, entation is maintained. These individuals, how-and their techniques may provide useful infor- ever, are all young males, highly trained, and inmation. In 1961, the present unofficial world top physical condition.record for a still-water dive was made by one Previous experimental water impacts with an-such individual diving 109 feet 7 inches into the esthetized guinea pigs, in an attempt to reproduceSea Circus pool at Pacific Ocean Park, Santa trauma in free-fall of the two 1954 Comet Air-Monica-the equivalent of an 11-story jump. line ruptures that spilled occupants into the sea,This same individual has jumped 155 feet into resulted in the conclusion that severe internal in-

5

juries may be expected in extreme water impact prone (-Gx) position, 93 ft/sec supine (+Gx),and that the critical velocity for guinea pigs was and 97 ft/sec head-first (-Gz). (Note that ye-about 104 ft/sec.28 Critical incident velocities locity calculations were corrected for aerody-for the mouse (118 ft/sec), guinea pig (99 ft/ namic drag and thus are lower than standardsec), and man (94 ft/sec) were predicted in a values.)separate study.29 Both of these previous the- C. No correlation between velocity (or distanceoretical and animal impact studies are in general of fall ) and degree of trauma was found; rather,agreement with the findings of these human free- injuries appeared to be more dependent uponfalls in water. body position at all levels of force. Severe in-

The etiology of these falls, particularly in cases juries (and fatalities )occurred at low levelsinvolving mental disorder, alcohol or drugs, may of velocity, while some cases of minimal or nobe of importance in evaluating each case of sur- injury occurred at very high-impact velocities.vival. As note previously, however, discrete data D. The pattern of impact injuries in the feet-as provided by most clinical histories do not pro- and buttocks-first position showed a high in-vide objective enough data in these water im- cidence (68%) of fractures, with compressionpacts to more than suggest a relationship. Many fractures to the first lumbar and twelfth thoracic

more intoxicated schizophrenics, for example, vertebrae the most common single injury. Bi-may survive extreme water impacts, but this lateral midshaft fractures were also typical incannot be scientifically interpreted without later m a fracture s werecalso itypialknolede o th toal ncienc-doproor- cases of fracture. Only 14% received internalknowledge of the total incidence-do propor- trauma, with lung hemorrhaging being most fre-

naetionatey more intoxicated schizophrenics jump- quent. Sixty-eight percent also received a dis-and are proportionately more thus also fatally tinctive pattern of contusions involving primar-injured? These are questions to be investigated ily the thigh and buttocks area. Eleven indi-in subsequent analysis of our fatal cases and, viduals of thirty-four (33%) received no clinicalparticularly, of the autopsy cases. trauma in feet-first impacts. Contrary to impact

V. Summary. findings on solid surfaces, no injuries to the feetor ankles occurred.

Forty-four cases of free-falls survived by in-dividuals impacting water environments under E. In lateral and transverse (prone and spine)conditions of high velocity (50 to 176 ft/sec) impacts in water, all individuals received in-

have been intensively investigated and analyzed. juries with 100% incidence of internal traumaAges varied from 7 to 80 years and the study (with renal hematoma most prevalent single in-included 34 males and 10 females. The falls jury )and 100% body contusions. Rib andoccurred in 17 different states primarily over a basalar skull fractures occurred in both lateral3-year period, and included attempted suicides, impacts, and compression fracture of the firstaccidental falls from high structures, and para- lumbar and twelfth thoracic vertebrae occurredchute failures in jumping or evacuating from in the supine position, with no fractures in theaircraft. one prone impact.

It was found that : F. There was a distinct correlation of age withA. The most survivable body orientation, by survival as the level of velocity was increased,

a factor of five to seven, is in a feet-first (+Gz) with both sexes showing higher impacts survivedimpact with arms over the head, due to increased at ages 20 to 36; however, since fatal cases weretime duration of deceleration caused by minimal not included, this could also reflect a higher ex-body-surface-area braking action. posure rate.

B. Critical velocity for human survival of G. Sex did not appear to a factor in survival.water impact in the feet-first body position ap-pears to be at about 100 f t/sec. Four cases H. Other factors considered to be of varyingranged from 100 to 116 ft/sec, and in two cases influence on water-impact survival included windterminal velocity was approached. The highest direction and velocity, water condition and cur-impact velocity survived was 87 ft/sec, in the rent, protective clothing, physical condition, men-lateral (-G,) body orientation, 88 ft/sec in the tal condition, and influence of alcohol or drugs.

6

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Survival of Extreme Vertical Impact in Seated Posi- and Joint Surg. 44-A(4) :648-656 (1962).tion, Civil Aeromedical Research Institute, Federal 28. Armstrong, J. A., Fryer, D.. I., Stewart, W. K., and

Aviation Agency, Oklahoma City, Oklahoma. 1962. Whittingham, H. E. Interpretation of Injuries in the13. Snyder, R. G., Human Tolerances to Extreme Im- Comet Aircraft Disasters, Lancet 268 (6875):1143

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14. Snyder, R. G. Infanticide and Aurora 7: Aeromed- Lung Injury by Impact With a Water Surfaceical Research in Extreme Human Deceleration, Nature 175:504-505 (1955).

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