Q: This is an article that we read regarding to G force: is it how they calculate the G force on the body at the time of the impact?
- "Forces Impacting the Accident Vehicles – deltaV
- The forces that impact a vehicle in an accident is referred to as “deltaV.” In a rear-end collision where a vehicle is stopped and is hit from behind by another vehicle, the impact’s force accelerates the struck or stopped vehicle forward from zero miles per hour to “x” miles per hour. That acceleration speed (velocity) of the struck vehicle is a positive deltaV. Meanwhile, the vehicle that struck the stopped car loses velocity and experiences a negative deltaV.
To calculate deltaV, most biomechanics experts use software such as CRASH III in which they input data about the vehicles, the accident site, and the vehicle damage (crush). From the calculation of deltaV, the expert can then calculate the g-forces involved in the accident. G-force is a measurement of the force to which a body is subjected when it is accelerated.
2. Forces Impacting the Accident Victim’s Body – Human Dynamics Analysis
- After deltaV is calculated, the insurance company’s expert will calculate what impact deltaV and g-forces had on the vehicle’s occupant. This calculation is known as “human dynamics analysis.” Like calculating deltaV, the engineer will input into a software program information about the deltaV and g-force along with other data to calculate whether the accident could have caused the plaintiff’s injuries."
A: Where did you read that article? We might add a link. Here are comments on that article:
First we do not agree with their statement that '
most biomechanics experts use software such as CRASH III'.
- CRASH3 is a simplified damage and momentum analysis procedure which has been demonstrated to have errors as great as +/-40%. One needs to use great caution if using or encountering the use of CRASH3 for individual accident reconstruction in litigated cases
Next we disagree with the statement that "
From the calculation of deltaV, the expert can then calculate the g-forces involved in the accident".
- DeltaV, calculated from CRASH tells you very little about the acceleration (G's) in an accident. Why? CRASH3 assumes instantaneous duration for the impact for both the damage analysis option and the trajectory option. Therefore if you use CRASH3 you have to assume a duration for collision, and then use the crude CRASH3 DeltaV and divide it by your assumed DeltaT: DeltaV/DeltaT and that only tells you a crude approximate 'average acceleration' for the collision.
And of course as mentioned earlier in this thread, Occupants do not sit at the CG so the acceleration at the CG may be quite different than what an individual occupant encounters at locations away from the CG due to the rotational movements and accelerations of the vehicle during the collision.
3rd we do not agree with the statement "
the engineer will input into a software program information about the deltaV and g-force along with other data to calculate whether the accident could have caused the plaintiff’s injuries":
- What software program? and what 'other data?'
Each and every human is different and all have different tolerances to accelerations. The NHTSA NASS program has been using CRASH3 to look at trends in injuries as they relate to deltaV and impact type for statistical studies however that is not for individual predictions and is not to 'calculate whether the accident could have caused' an injury.
The NASS program is to try to help NHTSA understand what types and severity of accidents produce the most injuries and then see what it is that might contribute to any injury.
NHTSA uses CRASH3 for uniform interpretation of evidence AND since some 90% of their reconstructions are 'damage only' and they like the simplicity of a CRASH3 damage analysis (they actually now use WinSMASH). They assume inaccuracies of CRASH3/WinSmash will not matter with the large statistical sample size).
The authors of that piece you sent also ignore differences in accelerations at different locations in the vehicle.
They also ignore the need to investigate what components of the vehicle did the occupant interact with during the 'second collision' (occupant into interior) which might have caused or exacerbated any injury.
Of course another thing to throw into the mix is the eggshell theory (which applies to other parts of the body i believe):
The
eggshell skull rule (or thin skull rule or you take your victim as you find him rule of the common law).