Understanding Car Crashes: When Physics Meets Biology

Understanding Car Crashes: When Physics Meets Biology


♪ MUSIC ♪ Griff Jones, Host:
WHY IS IT THAT SOME
SPECTACULAR RACE CAR CRASHES PRODUCE ONLY MINOR INJURIES? HOW CAN THREE COLLISIONS OCCUR
IN THIS ONE CRASH BETWEEN A CAR AND A WALL? THE ANSWERS ARE DETERMINED
BY THE LAWS OF NATURE AND CAN BEST BE EXPLAINED
WHEN PHYSICS MEETS BIOLOGY. THROUGH INJURY BIOMECHANICS, THE STUDY OF THE EFFECTS
OF FORCES ON THE HUMAN BODY, WE’VE LEARNED MUCH
ABOUT WHAT HAPPENS IN HIGH-SPEED RACE CAR CRASHES, AND DOCTORS AND ENGINEERS
HAVE USED THIS INFORMATION TO BUILD SAFER RACE CARS
AND TRACKS. IN A SIMILAR WAY, THE STUDY OF INJURY BIOMECHANICS
IN CRASH TESTING HAS HELPED US LEARN
WHAT HAPPENS TO THE HUMAN BODY IN PASSENGER CAR CRASHES AND WHAT WORKS AND DOESN’T WORK TO REDUCE INJURIES AND DEATHS
IN REAL-WORLD CRASHES. HI. I’M GRIFF JONES. I’M A SCIENCE TEACHER, AND I’M HERE AT THE INSURANCE
INSTITUTE FOR HIGHWAY SAFETY’S VEHICLE RESEARCH CENTER TO EXPLORE THE BASIC SCIENCE BEHIND INJURIES
IN VEHICLE CRASHES. SO LET’S GO BEHIND THE SCENES
AND TAKE A CLOSER LOOK AT WHAT HAPPENS
TO THE HUMAN BODY IN A CRASH. WHAT IS THE FIRST
SCIENTIFIC DISCIPLINE THAT COMES TO MIND
WHEN YOU THINK OF CAR CRASHES? IT’S PROBABLY PHYSICS, RIGHT? BECAUSE NEWTON’S LAWS OF MOTION GOVERN WHAT HAPPENS
TO A VEHICLE IN A CRASH. BUT IF WE WANT TO UNDERSTAND HOW CRASHES CAUSE INJURIES
TO PEOPLE, WE NEED LOOK AT WHAT OCCURS WHEN PHYSICAL FORCES ARE APPLIED
TO ORGANS, TISSUES, AND CELLS. THIS HAPPENS WHEN PHYSICS
MEETS BIOLOGY IN A FIELD CALLED
INJURY BIOMECHANICS. THE INSTITUTE’S
VEHICLE RESEARCH CENTER IS A WORLD-CLASS FACILITY FOR VEHICLE RESEARCH
AND TESTING. A REPORTER DESCRIBED
THE CRASH HALL WITH ITS THREE RUNWAYS AS “A CROSS BETWEEN
A HOLLYWOOD SOUND STAGE AND A NASA CLEAN ROOM.” VEHICLES ARE PROPELLED
DOWN THE RUNWAYS, AT PRECISE SPEEDS, USING A SYSTEM OF NITROGEN-POWERED
HYDRAULIC MOTORS AND CABLES. THE LIGHTING ARRAY PROVIDES UP TO 750,000 WATTS
OF NONGLARE ILLUMINATION FOR THE 500 FRAMES PER SECOND
HIGH-SPEED CAMERAS. THE RESEARCH TEST
THEY’RE CONDUCTING HERE TODAY FOCUSES ON HOW INJURIES OCCUR
IN REAL-WORLD CRASHES. THIS EXPERIMENTAL CRASH REPLICATES ONE
IN WHICH A CAR HIT A TREE. IN AN ATTEMPT TO UNDERSTAND
INJURY PATTERNS FOUND IN THE OCCUPANTS
OF THE ACTUAL CRASH, RESEARCHERS HAVE DISCONNECTED
THE AIRBAGS. Raul: LOOKING
AT THE DRIVER’S CHEST, WE CAN SEE THE CHEST DEFLECTION REACHED ABOUT 50 MILLIMETERS
OF COMPRESSION. THE CHEST ACCELERATION’S 70 TO 80 G RESULTANT
ACCELERATION RANGE. A HIGH LIKELIHOOD
OF SKULL FRACTURE. Raul: YEAH, VERY BAD. Griff: FIGURING OUT WHAT
JUST HAPPENED IN THIS TEST CRASH IS THE JOB OF
THE RESEARCH ENGINEERS HERE. USING SOPHISTICATED TOOLS LIKE
INSTRUMENTED CRASH TEST DUMMIES, INSTRUMENTATION IN THE CAR,
AND SLOW-MOTION FILM, THEY CAN ANALYZE EVERY DETAIL
AND CONSTRUCT A PRECISE PICTURE OF EXACTLY WHAT THE VEHICLE
AND THE OCCUPANTS WENT THROUGH. WHEN RESEARCH ENGINEERS
USE TERMS LIKE THE CHEST DEFLECTION
REACHED ABOUT 50 MILLIMETERS, HOW DOES THAT RELATE TO WHAT A HUMAN OCCUPANT
WOULD EXPERIENCE? IF CHEST ACCELERATION
IS 70 TO 80 Gs, WHICH MEANS
THAT A FORCE EQUIVALENT TO 70 TO 80 TIMES THE WEIGHT
OF THE DUMMY’S CHEST IS PRESSING ON IT, IS THAT SURVIVABLE? HOW DO THESE GUYS
KNOW THE ANSWERS? THE SEARCH FOR THE LIMITS
OF HUMAN TOLERANCE TO FORCES BEGAN DECADES AGO. TODAY’S RACE CAR
AND PASSENGER CAR DRIVERS BENEFIT FROM
BIOMECHANICS STUDIES THAT WERE CONDUCTED
DURING THE 1940s, ’50s, AND ’60s IN THE FIELD OF AVIATION, INVESTIGATING HOW TO PROTECT
PILOTS AND ASTRONAUTS FROM THE STRENUOUS FORCES OF
EJECTIONS IN HIGH-SPEED TRAVEL. COLONEL JOHN STAPP, A MEDICAL DOCTOR
AND BIOPHYSICIST IN THE UNITED STATES AIR FORCE, USED HIMSELF AS THE TEST SUBJECT
IN HIS INVESTIGATIONS OF HUMAN TOLERANCE
TO HIGH G ENVIRONMENTS. Announcer: FROM THE OUTSIDE,
WATCH THE BREAKNECK STOP. Griff: IN ONE OF HIS MANY TESTS, DR. STAPP REACHED A SPEED
OF 632 MILES PER HOUR BEFORE ONE OF THE MOST POWERFUL
BRAKING SYSTEMS OF ALL TIME STOPPED HIM IN 1.4 SECONDS, SUBJECTING HIM TO MORE THAN
40 TIMES THE PULL OF GRAVITY, OR 40 Gs. HIS RESEARCH HELPED ESTABLISH THE LIMITS OF HUMAN TOLERANCE
TO HIGH G ENVIRONMENTS AND SAVED MANY LIVES THROUGH
DEVELOPMENT AND IMPROVEMENT OF PROTECTIVE SYSTEMS
FOR EJECTION SEATS. REALIZING THE AIR FORCE
LOST NEARLY AS MANY MEN TO CAR CRASHES AS THEY DID
TO PLANE CRASHES, DR. STAPP BEGAN
A CAR CRASH PROGRAM USING THE ROCKET SLED
FOR SEAT BELT EXPERIMENTS. HUMAN VOLUNTEERS WORKING WITH
HIS BIOPHYSICS RESEARCH TEAM ENDURED AS MANY AS 28 Gs
DURING SAFETY BELT TESTS. THIS EARLY RESEARCH
LAID THE FOUNDATION FOR THE COMPLEX CRASH ANALYSIS
THAT IS CONDUCTED HERE TODAY. THESE DUMMIES
ARE A PERFECT EXAMPLE OF COMBINING SCIENCE,
TECHNOLOGY, ENGINEERING, AND MATHEMATICS TO PRODUCE NEW TOOLS THAT EXTEND
SCIENTIFIC UNDERSTANDING. THEY ARE THE MODERN DAY VERSION
OF DR. STAPP’S VOLUNTEERS. THERE’S NOT JUST ONE DUMMY FOR
VEHICLE RESEARCH CENTER TESTING, NOR EVEN ONE TYPE. THERE’S A WHOLE FAMILY
OF DUMMIES FOR CRASH TESTING. Marvin: THIS IS OUR
CRASH TEST DUMMY FAMILY, RANGING FROM A 6-MONTH-OLD ALL THE WAY UP
TO A 95th PERCENTILE MALE. Griff: 95th PERCENTILE OF WHAT? Marvin: THAT MEANS
THAT IT IS LARGER THAN 95% OF THE MALE POPULATION
IN THE U.S. Griff: WOW.
SO THIS IS A BIG GUY. Marvin: YES.
IF HE COULD STAND, HE WOULD BE ABOUT 6’2″,
ABOUT 223 POUNDS, PRETTY BIG. THE FEMALE, IF SHE COULD STAND,
ABOUT 5 FOOT TALL, 107 POUNDS. Griff: HOW ABOUT
THE SMALLER DUMMIES? Marvin: THEY ARE CALLED CRABIs. Griff: CRABIs?
ARE THEY MOODY? Marvin: THEY’RE NOT MOODY, BUT IT STANDS FOR CHILD
RESTRAINT AIR BAG INTERACTION. Griff: AND SO WHEN WE’RE DOING
THE FRONTAL CRASH TEST, IT’S 50th PERCENTILE. Marvin: YES. Griff: OKAY. SIDE IMPACT,
IT’S THE SMALL FEMALE. Marvin: THE SIDE IMPACT DUMMY
IS A VERY COMPLICATED DUMMY. IT HAS THE MOST INSTRUMENTATION. THEY HAVE SENSORS
FROM THE HEAD TO THE TOE. THE ACCELEROMETERS GIVE US
THE ACCELERATION OF THE MASS. THE LOAD CELL MEASURES FORCE, AND THEN WE HAVE
THE POTENTIOMETERS THAT MEASURE THE DISPLACEMENT
THE RIBS ACTUALLY MOVE. Griff: SO, DUMMIES
ARE VERY SOPHISTICATED. THEY PROVIDE DATA FROM
MANY DIFFERENT BODY REGIONS, BUT HOW DO WE CONNECT THIS
TO PEOPLE? WHAT IS THE LINK BETWEEN
ALL THESE CRASH TEST DATA AND THE INJURIES
THAT PEOPLE EXPERIENCE IN REAL-WORLD CRASHES? David Zuby: THE DUMMY’S
MEASURING DIFFERENT THINGS. IT’S MEASURING
ACCELERATION, FORCE, AND IN SOME CASES DISTORTION OF THE BODY PARTS. THOSE MEASUREMENTS
CAN BE COMPARED AGAINST SIMILAR MEASUREMENTS MADE IN EXPERIMENTS
ON BIOLOGICAL TISSUES USING EITHER ANIMAL MODELS
OR CADAVER MODELS TO GET AN IDEA OF HOW MUCH
STRESS CAN THIS BODY PART TAKE BEFORE IT BREAKS? SO IN ORDER TO UNDERSTAND WHETHER OR NOT A PERSON
WOULD BE INJURED, YOU NEED TO KNOW
HOW STRONG THE BONES ARE, HOW STRONG THE TISSUES ARE, AND WHAT CONDITIONS
WILL CAUSE THEM TO BREAK. Griff: SO THE CRASH TEST DUMMIES
TRY TO GET A CLEAR PICTURE OF WHAT’S REALLY HAPPENING
TO THE PEOPLE. IS THAT WHERE THE TERM
“BIOFIDELITY” COMES FROM? David: IT’S EXACTLY WHERE
THE TERM BIOFIDELITY COMES FROM. WHAT BIOFIDELITY MEANS IS
THE CHARACTERISTIC OF THE DUMMY THAT REPRESENTS HOW CLOSE TO ACTUALLY BEING
A HUMAN BEING IT IS. SO THE HIGHER THE BIOFIDELITY, THE MORE LIKE
A HUMAN BEING IT IS IN REPRESENTING HOW IT MOVES, WHAT TYPES OF STRESSES
IT MEASURES IN THE CRASH TEST, AND THEN THE TRUE-TO-LIFENESS
OF THOSE MEASUREMENTS TO THE PREDICTION OF INJURY
IN A REAL PERSON. Griff: THIS IS HOW
RESEARCH ENGINEERS CAN TELL US WITH PRECISION WHAT A HUMAN OCCUPANT WOULD HAVE
EXPERIENCED IN A TEST CRASH. DR. STAPP’S EXPERIMENTS
PLUS YEARS OF RESEARCH WITH REAL BIOLOGICAL TISSUES
FROM CADAVERS AND ANIMALS HAVE PRODUCED A SET
OF REFERENCE VALUES AGAINST WHICH WE CAN COMPARE THE STRESSES AND STRAINS
THE DUMMIES EXPERIENCE. SO WE CAN MEASURE THESE
IN A TEST CRASH AND CAN FIGURE OUT IF THEY WOULD CAUSE INJURY
TO A HUMAN OCCUPANT. BUT WHAT DO THESE
STRESSES AND STRAINS ACTUALLY DO TO PEOPLE
TO CAUSE INJURY? LET’S START
WITH SOME BASIC ANATOMY. YOUR BODY CONTAINS
OVER 100 TRILLION CELLS AND IS STRUCTURALLY ORGANIZED
INTO FOUR LEVELS: CELLS, TISSUES, ORGANS,
AND ORGAN SYSTEMS. TISSUE IS A GROUP
OF SIMILAR CELLS WORKING TOGETHER
TO PERFORM A COMMON FUNCTION. ORGANS ARE MADE UP
OF TWO OR MORE TYPES OF TISSUE WORKING TOGETHER
TO PERFORM A SPECIFIC FUNCTION, AND EACH ORGAN IS PART
OF AT LEAST ONE ORGAN SYSTEM THAT PERFORMS MAJOR ACTIVITIES
OR PROCESSES. YOUR BODY CONTAINS
FOUR FLUID-FILLED SPACES CALLED BODY CAVITIES THAT HOUSE AND PROTECT
YOUR MAJOR INTERNAL ORGANS. WITHIN THE BODY CAVITIES YOUR ORGANS ARE SUSPENDED
IN FLUID THAT SUPPORTS THEIR WEIGHT AND PREVENTS THEM FROM BEING
DEFORMED BY NORMAL MOVEMENTS. YOUR ORGANS ARE ALSO PROTECTED
BY YOUR BONES AND MUSCLES. FOR EXAMPLE,
YOUR HEART AND LUNGS ARE PROTECTED BY
YOUR RIB CAGE AND STERNUM INSIDE THE THORACIC CAVITY. YOUR BRAIN IS ENCASED
WITHIN YOUR CRANIAL CAVITY AND IS PROTECTED BY YOUR SKULL. NOW WITH THIS AS BACKGROUND, REMEMBER THE QUESTION FROM
THE BEGINNING OF THIS FILM– HOW IS IT POSSIBLE TO HAVE THREE
COLLISIONS IN A SINGLE CRASH? REMEMBER, THE LAWS OF PHYSICS
HOLD TRUE EVERYWHERE– ON A HIGHWAY, ON A RACE TRACK,
AND EVEN INSIDE YOUR BODY. IF A RACE CAR IS GOING
200 MILES PER HOUR, SO IS THE DRIVER’S BODY
AND EVERY ORGAN INSIDE IT. LET’S ANSWER THE QUESTION. THE FIRST COLLISION
IS BETWEEN THE CAR AND THE WALL. THE SECOND IS BETWEEN THE DRIVER
AND THE CAR’S INTERIOR, AND THE THIRD IS BETWEEN
THE DRIVER’S INTERNAL ORGANS AND THE INSIDE WALLS
OF HIS OR HER BODY CAVITIES. TO HELP US UNDERSTAND MORE ABOUT WHAT HAPPENS TO ORGANS
IN THE THIRD COLLISION, LET’S MEET DR. STEPHEN OLVEY,
A NEUROCRITICAL CARE PHYSICIAN AND DIRECTOR OF THE NEUROSCIENCE
INTENSIVE CARE UNIT AT THE UNIVERSITY OF MIAMI’S
JACKSON MEMORIAL HOSPITAL. Dr. Olvey:
BASICALLY DURING A CRASH,
YOU HAVE THREE COLLISIONS. YOU HAVE THE INITIAL CRASH
OF THE VEHICLE. THEN YOU HAVE THE OCCUPANT
HITTING SOMETHING INSIDE THE CAR AND COMING TO A SUDDEN STOP. THIS RESULTS IN IMPACTS
INSIDE THE BODY. FOR EXAMPLE, THE LUNGS CAN HIT
THE INSIDE OF THE RIB CAGE. THE HEART CAN HIT
THE BREAST BONE OR INSIDE OF THE RIB CAGE, RESULTING IN EITHER
A PULMONARY CONTUSION OR MYOCARDIAL CONTUSION. THIS IS WHAT CAUSES RUPTURED
SPLEENS, LACERATED LIVERS, BECAUSE YOU HAVE
PART OF THE ORGAN WELL ANCHORED AND THE OTHER PART
IS FREE TO MOVE ABOUT. AND THIS CAUSES A SHEARING FORCE
TO TAKE PLACE IN THE ORGAN RESULTING IN HEMORRHAGE
OR TEARING OF THE TISSUE. THE BRAIN IS ENCLOSED
IN A RIGID CASE, THE SKULL, AND IT’S CUSHIONED
AND SURROUNDED BY THE CEREBRAL SPINAL FLUID. THE CEREBRAL SPINAL FLUID IS ACTUALLY A DIFFERENT DENSITY
THAN THE BRAIN ITSELF. SO IN THE EVENT OF AN IMPACT
TO THE SKULL, THE BRAIN BEGINS TO MOVE, THE CEREBRAL SPINAL FLUID
BEGINS TO MOVE, BUT IT MOVES AT A DIFFERENT RATE
THAN THE BRAIN. SO IT’LL ACTUALLY
DISPLACE THE BRAIN IN THE OPPOSITE DIRECTION OF
THE INITIAL IMPACT TO THE BRAIN. Griff: THIS SIMPLE EXPERIMENT
HELPS ILLUSTRATE THE PHENOMENON. THIS REPRESENTS YOUR SKULL. THERE’S WATER INSIDE REPRESENTING YOUR
CEREBRAL SPINAL FLUID, AND THE RED GEL IS YOUR BRAIN. THE GEL FLOATS BECAUSE
IT’S LESS DENSE THAN WATER, JUST LIKE YOUR BRAIN
IS LESS DENSE THAN YOUR CEREBRAL SPINAL FLUID. WHAT DO YOU THINK WILL HAPPEN
TO THE BRAIN DURING IMPACT? WILL IT MOVE FORWARD, BACKWARD,
OR STAY IN THE SAME SPOT? LET’S SEE. THE INITIAL MOVEMENT
OF THE BRAIN IS TOWARD THE BACK OF THE SKULL. THE MORE DENSE
CEREBRAL SPINAL FLUID MOVES TOWARD THE SITE
OF SKULL IMPACT DISPLACING THE BRAIN
IN THE OPPOSITE DIRECTION. IF THE IMPACT IS STRONG ENOUGH, THE BRAIN WILL INITIALLY IMPACT
THE BACK WALL OF THE SKULL THEN REBOUND AND HIT
THE FRONT OF THE SKULL. THIS TYPE OF INJURY
IS CALLED A COUP-CONTRECOUP, WHICH IS A FRENCH TERM MEANING
“BLOW AGAINST BLOW.” THE ORDER OF EVENTS
INSIDE THE SKULL IS STILL DEBATED
IN THE MEDICAL COMMUNITY. WHETHER THE MORE DENSE FLUID DISPLACES THE BRAIN
IN THE OPPOSITE DIRECTION FIRST, OR WHETHER THE BRAIN MOVES IN THE DIRECTION
OF THE INITIAL IMPACT FIRST AND THEN IS DISPLACED
BY A WAVE OF SPINAL FLUID, IS NOT YET FULLY UNDERSTOOD. BY THE WAY, THIS SIMPLE
EXPERIMENT WAS DESIGNED BY A HIGH SCHOOL STUDENT
FOR HER SCIENCE FAIR PROJECT. IT WAS LATER PUBLISHED
IN A MEDICAL JOURNAL AND HAS CONTRIBUTED
TO THE DEBATE. CRASH INJURIES OCCUR
WHEN STRESS DEVELOPS IN TISSUE. ANOTHER WAY THIS HAPPENS IS WHEN
ONE PART OF THE TISSUE OR ORGAN IS FIRMLY ATTACHED TO THE TORSO AND ANOTHER PART
IS FREE TO MOVE. FOR EXAMPLE, WITH THE HEART
AND ITS BLOOD VESSELS THE ASCENDING AORTA
AND ITS ARCH ARE MOBILE, WHILE THE DESCENDING AORTA
IS FIXED. HERE’S A DEMONSTRATION
OF HOW A SUDDEN STOP LIKE A THIRD COLLISION CAN CAUSE AN ACCELERATION INJURY
TO THE AORTA. THE AORTIC ARCH IS REPRESENTED
BY THE UNSUPPORTED GEL. THE GEL INSIDE THE TUBE
REPRESENTS THE DESCENDING AORTA WHICH IS FIXED TO THE BODY. TRY TO PREDICT WHAT WILL HAPPEN
DURING THE COLLISION. THE UNSUPPORTED SECTION OF GEL
CONTINUES FORWARD AND TEARS AWAY
FROM THE SUPPORTED GEL. DURING AN ACTUAL COLLISION, THE FIXED DESCENDING AORTA WILL
DECELERATE ALONG WITH THE BODY, WHILE THE ARCH AND
ASCENDING AORTA’S MOMENTUM KEEP THEM MOVING FORWARD. THIS DIFFERENCE IN ACCELERATION
OR DECELERATION CAUSES A TEAR WHERE THE FIXED
AND MOBILE PARTS MEET. EVEN THE INERTIA
OF A BLOOD-FILLED HEART CAN CAUSE STRESS AND STRAIN
ON THE AORTIC ARCH. WE’VE BEEN TALKING
ABOUT STRESS AND STRAIN ON TISSUES AND ORGANS, AND WE’VE SEEN HOW A CRASH
APPLIES SOME OF THESE FORCES. BUT WHAT IS STRESS AND STRAIN
IN THIS CONTEXT? STRESS IS A MEASURE OF
THE AVERAGE DEFORMING FORCE EXERTED OVER A DEFINED AREA
OF TISSUE. STRESS PRODUCES STRAIN, WHICH IS A MEASURE OF
HOW MUCH THE TISSUE DEFORMS AS A RESULT OF THE STRESS. THIS SPECIAL GEL
HAS ELASTIC PROPERTIES SIMILAR TO CERTAIN HUMAN TISSUE, BUT NOT ALL HUMAN TISSUE
IS OF EQUAL STRENGTH. FORCES AND PRESSURES
ON THE OUTSIDE OF YOUR BODY CAUSE STRESS WITHIN YOUR TISSUE. THREE BASIC TYPES OF STRESS ARE
TENSILE STRESS FROM STRETCHING, SHEARING STRESS
FROM OPPOSING FORCES, AND COMPRESSIVE STRESS
FROM UNIFORM COMPRESSION. ENGINEERS JUDGE THE SAFETY
OF A BRIDGE BY COMPARING THE STRESS
ON THE BRIDGE TO THE STRENGTH
OF THE BUILDING MATERIALS. EVERY MATERIAL,
WHETHER IT’S CONCRETE OR DIFFERENT TYPES
OF HUMAN TISSUE, HAS A CRITICAL STRESS LIMIT. STAY BELOW THE LIMIT, AND THERE
IS NO DAMAGE OR FAILURE. GO BEYOND THE STRESS LIMIT,
AND THERE IS FAILURE. TRAUMA TO HUMAN TISSUE
IS LIKE FAILURE TO A STRUCTURE. HERE’S A BLOCK
OF OUR SPECIAL GEL. A COMMON TYPE OF CRASH TRAUMA
IS BLUNT FORCE, A NONPENETRATING TYPE
OF INJURY FROM A BODY HITTING
A ROUNDED OR DULL OBJECT OR VICE VERSA. THE IMPACT PRODUCES A SHOCKWAVE
THAT MOVES THROUGH THE BODY, SIMILAR TO A SOUND WAVE
MOVING THROUGH AIR. I’M HITTING THIS GEL
WITH A MALLET, WHICH WILL PRODUCE A SHOCKWAVE
THAT IS VISIBLE IN SLOW MOTION. THESE WAVES CHANGE SPEED
AND/OR DIRECTION AS THEY MOVE THROUGH TISSUES
OF DIFFERING DENSITIES, PRODUCING COMPLEX
WAVE INTERACTIONS THAT CAUSE STRESS AND STRAIN
IN TISSUES AND ORGANS. BIGGER AND MORE CONCENTRATED
IMPACT FORCES PRODUCE BIGGER AND POTENTIALLY
MORE DAMAGING SHOCKWAVES, THUS MORE, AND POTENTIALLY
MORE DAMAGING, STRESS AND STRAIN. IF THE TYPE AND SIZE
OF THE STRESS EXCEEDS THE STRENGTH
OF THE TISSUE, THEN AN INJURY OCCURS. BUT WHAT EXACTLY IS IT THAT
SHOCKWAVES DO TO INJURE TISSUE? AS SHOCKWAVES MOVE
THROUGH TISSUE, THEY DISRUPT FUNCTION
AT THE CELLULAR LEVEL. Dr. Olvey: YOU ACTUALLY GET
INJURY TO THE CELLS THEMSELVES, AND THEY BEGIN TO MALFUNCTION. YOU GET POTASSIUM, GLUTAMINE,
AND GLUCOSE LEAVING THE CELL, CALCIUM ENTERING THE CELL. IN A BRAIN INJURY, THIS SHIFT
OF IONS WITHIN THE BRAIN CAUSES THE RELEASE OF CHEMICALS
THAT CAN INTERFERE WITH THE BRAIN’S ABILITY
TO REGULATE ITS OWN BLOOD FLOW, AND THEREFORE ITS DELIVERY OF
OXYGEN TO THE INDIVIDUAL CELLS. THIS FAILED AUTO-REGULATION,
AS IT’S CALLED, CAN CAUSE AREAS OF THE BRAIN
TO BECOME ISCHEMIC. THAT MEANS THEY DON’T
GET THE OXYGEN DELIVERED THAT’S NECESSARY TO FUNCTION, AND THEREFORE THEY’RE AT RISK
OF MALFUNCTION TO THE POINT OF CELL DEATH. IT’S A CHAIN REACTION
OR A CASCADE OF CHEMICAL EVENTS THAT TAKES PLACE
AT THE CELLULAR LEVEL. Griff: WE’VE SEEN HOW INJURIES
OCCUR IN CRASHES. HIGH FORCES CREATE SHOCKWAVES,
WHICH IN TURN CREATE STRESS THAT CAN CAUSE
TISSUES AND ORGANS TO STRETCH, TEAR, OR COMPRESS. THIS STARTS A CASCADE OF EVENTS
THAT CAN LEAD TO CELL DEATH. SO WHAT IS THE KEY
TO REDUCING CRASH INJURIES? IT’S REDUCING FORCES
ON VEHICLE OCCUPANTS. DR. OLVEY’S DAY JOB IS
SAVING LIVES AT THE HOSPITAL. IN HIS OTHER CAREER, HE’S A PIONEER IN THE FIELD
OF RACE MEDICINE AND CHIEF MEDICAL OFFICER FOR THE GRAND PRIX MASTERS
RACING SERIES. DR. OLVEY ORGANIZED
THE FIRST TRAVELING MEDICAL TEAM IN MOTOR SPORTS. BEGINNING IN THE EARLY 1980s,
HE AND HIS COLLEAGUES BEGAN COLLECTING DATA
RELATED TO RACE CRASH INJURIES IN ORDER TO IDENTIFY TRENDS
AND METHODICALLY STUDY INJURIES. IN 1993, OLVEY’S TEAM BEGAN
TO USE PROFESSIONAL AUTO RACING AS A LABORATORY TO COLLECT
AND ANALYZE DATA FROM ONBOARD CRASH RECORDERS. THIS LED TO SIGNIFICANT
SAFETY IMPROVEMENTS IN RACE CAR AND TRACK DESIGN. NOW THEY HAVE SOME INNOVATIONS
IN THE WALL AS WELL, SO THAT THE WALL
HAS SOME GIVE TO IT. Dr. Olvey: IT’S CALLED
THE “SAFER WALL,” AND IT’S A SERIES
OF STYROFOAM PLATES BEHIND THE BARRIER THAT ABSORBS THE SHOCK
OF AN IMPACT. AND IT REALLY CUTS THE STRENGTH
OF THE IMPACT BY 40% TO 60%. YOU’VE HEARD ABOUT
CRASH RECORDERS IN AIRPLANES. WELL, WE HAVE CRASH RECORDERS
IN RACE CARS AS WELL. THIS BOX HAS
TRIAXIAL ACCELEROMETERS, WHICH MEASURE ACCELERATIONS
IN THREE DIRECTIONS: VERTICAL, HORIZONTAL,
AND LONGITUDINALLY. SO IN THE EVENT OF A CRASH THEY CAN TAKE THE DATA
OFF OF THIS RECORDER, TAKE IT BACK TO THE LABORATORY, KNOW EXACTLY WHAT THE DRIVER
WENT THROUGH IN THAT CRASH. THIS ALLOWS YOU
TO MAKE COMPUTER MODELS AND RE-ENACT THE CRASH, AND YOU CAN MAKE CHANGES
TO THE CAR. Griff: ADVANCES
IN MOTOR SPORTS SAFETY BROUGHT ABOUT BY THE STUDY
OF INJURY BIOMECHANICS HAVE MADE A BIG DIFFERENCE IN DRIVERS BEING ABLE
TO SURVIVE HIGH-SPEED CRASHES. Announcer:
HE’S GONNA UNBOLT HIMSELF
FROM THE SIX-WAY HARNESS. Griff: SAFETY FEATURES
LIKE SIX-POINT HARNESSES, RIGID SAFETY CAGES OR “TUBS,” ENERGY ABSORBING
“HEAD SURROUNDS,” BREAKAWAY PARTS,
AND ENERGY-ABSORBING WALLS HAVE CONTRIBUTED
TO REDUCING FORCES ON DRIVERS AND PREVENTING INJURIES. IN THE VEHICLES WE DRIVE,
THE STUDY OF INJURY BIOMECHANICS HAS CONTRIBUTED TO HUGE
IMPROVEMENTS IN VEHICLE DESIGN. MANY OF THESE IMPROVEMENTS HAVE RESULTED FROM THE WORK
OF THE VEHICLE RESEARCH CENTER. THIS IS ADRIAN LUND. HE’S PRESIDENT OF THE INSURANCE
INSTITUTE FOR HIGHWAY SAFETY. Adrian Lund: YOU TRY TO DESIGN
THE STRUCTURE OF THE CAR SO THAT IT CRUSHES IN FRONT, SO YOU’RE BRINGING THE CAR
TO A STOP SLOWLY OVER TIME. IF YOU BRING THE CAR
TO A STOP SLOWLY, THAT GIVES YOU TIME
TO PROTECT THE OCCUPANTS INSIDE, SO THAT’S A LITTLE EXTRA TIME FOR YOU TO MANAGE THE OCCUPANT”
KINETIC ENERGY. WE HAVE A GOOD SAFETY CAGE HERE. THAT MEANS THAT THERE’S
PLENTY OF ROOM FOR THE BELT AND THE AIRBAG TO GIVE THEM
MORE RIDE-DOWN SPACE. SO EVEN AFTER THE FRONT OF
THE VEHICLE HAS COME TO A STOP, THE SAFETY BELT
CAN STRETCH A LITTLE FURTHER, THE AIRBAG WILL DEFLATE,
AND THEY CAN RIDE THAT DOWN. WE’RE FINDING WAYS
THROUGH OUR RESEARCH TO LENGTHEN THAT AMOUNT OF TIME
OVER WHICH THESE CHANGES OCCUR. Griff: HERE’S A CHALLENGE
I GIVE MY STUDENTS: DESIGN AN EGG-CARRYING CAR
FROM ONLY TWO SHEETS OF A PAPER BUT WITH UNLIMITED AMOUNTS
OF GLUE. I PROVIDE THE WHEELS AND AXLES, BUT THEY MUST APPLY THEIR
SCIENCE KNOWLEDGE AND SKILLS TO PRODUCE A CRASHWORTHY VEHICLE
THAT PROTECTS THE EGG. THE CAR WITH THE MOST MOMENTUM
THAT IS ABLE TO PROTECT THE EGG IS DECLARED THE WINNER. Griff: SAFE CAR…
NO INJURIES! Adrian: NOW IN A SIDE IMPACT IT’S ACTUALLY PRETTY HARD
TO INCREASE THE TIME, SO THE OTHER THING WE DO
IS TO TRY TO SPREAD THE FORCES OVER A LARGER PORTION
OF THE BODY SO THAT NO PART OF THE BODY EXPERIENCES FORCES
THAT WILL CAUSE INJURY. IF YOU DON’T DO THAT, THEN MAYBE
THE ARMREST JUST COMES IN AND IT HITS YOU AT ONCE AND IT’S TRYING TO ACCELERATE
YOUR WHOLE BODY JUST BY PUSHING ON YOUR ABDOMEN,
AND THEN YOU HAVE INJURIES. Griff: YOU’VE GOT MORE FORCE
IN A CONCENTRATED AREA. YOU’VE GOT MORE PRESSURE, SO YOU’VE GOT
MORE STRESS AND STRAIN, WHICH DAMAGES
TISSUES AND ORGANS. Adrian: THAT’S RIGHT. Griff: FORCE AND PRESSURE
ARE CLOSELY RELATED, BUT THEY ARE NOT THE SAME THING. HERE IS A MORE DRAMATIC
DEMONSTRATION OF THE DIFFERENCE. CAN YOU EXPLAIN
WHY THE VERY SHARP NAILS– TRUST ME, THEY ARE SHARP–
DO NOT PUNCTURE MY SKIN? NO, IT’S NOT MAGIC. IT IS BECAUSE MY WEIGHT
IS DISTRIBUTED FAIRLY EVENLY OVER THE NAILS. THE TRICK IS TO HAVE
A LARGE NUMBER OF NAILS. PRESSURE IS EQUAL TO THE FORCE
EXERTED ON A SURFACE DIVIDED BY THE TOTAL AREA
OVER WHICH THE FORCE IS EXERTED. THE MORE NAILS WE HAVE
IN OUR BOARD, THE GREATER THE TOTAL
SURFACE AREA I AM LYING ON, AND THE LOWER MY PRESSURE
ON ANY ONE NAIL. MORE NAILS MEANS LESS PRESSURE. WE HAVE SO MANY NAILS
IN OUR BOARD WE ARE GOING TO PUT A 223-POUND
CRASH DUMMY ON MY CHEST. EVEN THOUGH THE FORCE
HAS INCREASED, THERE ARE STILL ENOUGH NAILS
TO KEEP THE PRESSURE AT A SAFE, ALTHOUGH
RATHER UNCOMFORTABLE, LEVEL. Adrian: IT USED TO BE
THAT CRASHES WERE ALWAYS REFERRED TO
AS ACCIDENTS, BUT THAT DOESN’T TELL YOU
HOW TO PREVENT THEM. WHAT TELLS YOU
HOW TO PREVENT THEM IS TO REALIZE
THAT THIS IS A CRASH. IT’S A PHYSICAL THING. IT’S PREDICTABLE. IT HAS PREDICTABLE CONSEQUENCES. IT’S JUST THE PHYSICS
AND THE BIOLOGY. Griff: WHETHER IT’S
ON A RACE TRACK, A ROCKET SLED, OR ON THE HIGHWAY, THE PRINCIPLES ARE THE SAME. WHEN FORCES ARE HIGH
ON THE OCCUPANTS, THERE IS POTENTIAL FOR DAMAGE
TO TISSUE AND ORGANS. KEEPING PEOPLE SAFE IN CRASHES HAS TO DO WITH EXTENDING
IMPACT TIME, KEEPING THE OCCUPANT COMPARTMENT
INTACT, AND TYING THE OCCUPANTS
TO THE COMPARTMENT. WHAT HAPPENS TO THE HUMAN BODY
DURING A CRASH IS DETERMINED BY BIOLOGY
AND PHYSICS. YOU CAN’T ARGUE
WITH HARD SCIENCE. ♪ SINCE I CRASHED INTO YOU… ♪ Griff: BUT WHAT DO
STRESS AND STRAIN MEAN? THREE BASIC TYPES OF STRESS ARE TENSILE STRESS
FROM STRETCHING… Announcer: WHOA. UPSIDE DOWN. Griff: THIS HAPPENS
WHEN BIOLOGY MEETS PHYSICS. OOPS. WHEN PHYSICS
MEETS BIOLOGY. ♪ SINCE I CRASHED INTO YOU ♪ ♪ I GOT ALL I EVER WANTED TO ♪ ♪ I GOT EVERYTHING
SINCE I CRASHED ♪ ♪ SINCE I CRASHED INTO YOU ♪ ♪ DOESN’T MATTER
WHAT I’M GOIN’ THROUGH ♪ ♪ I GOT EVERYTHING
SINCE I CRASHED INTO YOU ♪ ♪ INTO YOU ♪