Information from a previous part of my life:
The original Head Injury Criteria later used in Federal Motor Vehicle Standard 208 was generated by dropping embalmed cadaver heads onto unyielding, flat surfaces, striking the subject on the forehead. The WSTC (Figure 2-1) provides a relationship between peak acceleration, pulse duration, and concussion onset. In the original work, skull fracture was used as the criterion for determination of concussion and the onset of brain injury. The final form of the Wayne State Tolerance Curve was published by Gurdjian (Gurdjian 1963, Patrick 1963). In its final form, the WSTC was developed by combining results from a wide variety of pulse shapes, cadavers, animals, human volunteers, clinical research, and injury mechanisms. Skull fracture and/or concussion was used as the failure criterion, except for the long duration human volunteer tests in which there were no apparent injuries.
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| The math behind the Head Injury Criteria |
In English rather than mathematical expression, a sliding time window 0.032 seconds long is moved along the acceleration trace for the crash-dummy's head. The average acceleration for the 0.032 second window is raised to the 2.5th power. The maximum HIC value for the entire time-trace is the HIC reported for the event.
The Physics
Brains are jelly-like and a shock is treated like a center-pass filter. A very fleeting shock, even though very high, does not last long enough to cause the entire brain to slosh across the cranial cavity.
It is counter-intuitive, but the primary damage to the brain is not on the high-pressure side. Being jelly-like, or liquid(ish), the brain is resistant to pressure as long as it doesn't squirt out of the skull. The primary damage occurs on the low pressure side where dissolved gasses expand explosively and rupture cells and blood vessels.
Consequently, a blow to the forehead can cause damage to the rear of the occipital lobe processes visual signals and works cooperatively with many other brain areas. The occipital lobe plays a crucial role in language and reading, storing memories, recognizing familiar places and faces which explains why people with closed-head injuries often have slow and halting speech.
More Physics
In a frontal car accident there are three collisions.
The first collision is when the bumper hits the object in front of the vehicle. The motor compartment side rails start to crumple and the body of the vehicle starts to slow down. Meanwhile, the bodies of the occupants and the engine merrily fly through space, not yet "knowing" that the body is slowing down.
Then the engine hits the object and starts loading into the motor compartment side rails and adds to the decel rate. The decel rate increases even as the occupants continue sailing across the free-space within the passenger compartment.
If there were air-bags, the bags already fully inflated and are starting to deflate. Air bags dissipate energy as the occupants hit them and air (hot CO2, actually) is squeezed out through the loose weave of the fabric. If the bags did not deflate in a controlled manner, the passenger's heads would bounce and be subjected to much higher rates of force.
The body of the car + engine is REBOUNDING from the wall when the occupant(s) finally impact the interior of the vehicle. It is very possible for a 30 mph collision to turn into a 37 mph net velocity change as the vehicle bounces backwards. That is a big deal because energy increases with the square of the velocity and a 20% increase in net velocity change means the restraint systems need to deal with 44% more energy.
What I see when I watch this image is that the man's head bounces after the first impact. That tells me that he didn't smash his teeth/jaw at that point. It also tells me that his head saw very high g forces and he is a likely candidate for the morgue. No airbags or plastic deformation of a steering wheel to help him out, there.
The second impact had no head bounce and the energy was probably dissipated by jaw fracture.
The combat medic told me a fall from anything higher than the person is tall, is potential fatal. He also mentioned hand supination as a tell-tale of massive brain injury. The guy's hands are relaxed, not turned inward, so it was a quick death.
ReplyDeleteAfter my concussion, I don't tolerate watching stuff like that well. I'm not sure why. I just nope right on out.
Darwinism is alive and functioning, or hold my beer and watch this.
ReplyDeleteSo THAT'S what my problem is!
ReplyDeleteHead injuries can get 'freaky' with the damage done far outweighing the minimal original impact
ReplyDeleteIt did look pretty hard on the guy.
ReplyDeleteSomething to consider is that, in addition to the impacts your video (painfully) captures, there are the second and second (exponent) 2 impacts. Impact 2 is the brain, traveling at (whatever speed he has achieved in his fall) striking the now immobile skull, as he has impacted the pool deck the first time.
ReplyDeleteImpact -exponent-2, is the brain striking the inside of the skull as his head strikes the pool deck the second time.
Even if nothing else is happening (and it is), the back-and-forth is not kind to the arteries and veins that connect the brain, sort of floating in the cranium, to the source vessels, firmly fixed in that self same cranium.
How one acquires a subdural hematoma.
My specialty is imaging. And I have almost half a century of experience. You would be utterly amazed at how much trauma humans can endure including head injuries, and survive, often with little obvious injury or damage. And often how little it takes to kill or permanently injured someone. It's a bizarre contradiction but a real one. In this case I suspect the victim probably survived with a concussion and possibly intracranial hemorrhage. Though death is of course a possibility. He may have suffered facial fractures also. Facial bones often act as a cushion preventing skill fracture and lessening brain injury.
ReplyDeleteThank God there was no sound with that video.
ReplyDeleteI think that is called a dead cat bounce.
ReplyDelete