Quantification of injuries vs impact speed change (DeltaV) question

[MSI]

Q: I do research in the area of Biomechanics of human body. Would you be kind and help me? If we know the weight of 2 vehicles and the speed of the cars at the time of the accident and the individual age and weight, do you have a software that can help to measure the damage to the body based on the G force created and V vector? Like injury risk etc?

A: There has been and continues to be a lot of research on Impact Speed Change (deltaV) and associating injuries to exposure to DeltaV.
What is deltaV? See What is DeltaV? A Discussion
For some discussions of some of the issues associated with trying to ‘measure damage to the body based on the G force created and V vector’

• Some background is available at Articulated Total Body (ATB) papers
• Those papers are primarily about the ATB program but also applies to the MADYMO program and any other program trying to predict occupant injuries.
• References cited it those papers include much research has been done trying to categorize the thresholds for injuries and associate them with accident severity exposure (DeltaV)

Once you’ve had a chance to review the links and papers available through the links let me know if you have any additional question.

[MSI]

A couple additional areas to review would be on the nhtsa.gov site.

• National Automotive Sampling System (NASS) is a project by NHTSA which includes:
  • Crashworthiness Data System Overview
    • NASS CDS has detailed data on a representative, random sample of thousands of minor, serious, and fatal crashes. Field research teams located at Primary Sampling Units (PSU's) across the country study about 5,000 crashes a year involving passenger cars, light trucks, vans, and utility vehicles. Trained crash investigators obtain data from crash sites, studying evidence such as skid marks, fluid spills, broken glass, and bent guard rails. They locate the vehicles involved, photograph them, measure the crash damage, and identify interior locations that were struck by the occupants. These researchers follow up on their on-site investigations by interviewing crash victims and reviewing medical records to determine the nature and severity of injuries.
      Interviews with people in the crash are conducted with discretion and confidentiality. The research teams are interested only in information that will help them understand the nature and consequences of the crashes. Personal information about individuals - names, addresses, license and registration numbers, and even specific crash locations - are not included in any public NASS files.
  Biomechanics & Trauma
  • Biomechanics & Trauma conducts cooperative and collaborative research with other organizations around the world to develop tools that help mitigate injury and death in motor vehicle crashes. Crash test dummies are developed and tested, and NHTSA’s fleet of crash test dummies are maintained within this group.

The software that McHenry Software develops and markets, msmac3D, is to allow for more accurate 3D reconstruction of collisions and accidents which can help better quantify the acceleration environment that the occupants of a vehicle undergo.

[MSI]

Q: I do appreciate you. Still trying to locate any formula or software that can show the amount of impact (or force) on human body after the collision with low speed or high speed collision. Knowing the weight of the 2 cars and the velocity and speed at the time of the collision, would it help to calculate the G force on the driver’s body to injure neck or low back? Dr Panjabi did some research at Yale but he is retired.

A: A quick summary is in order:

• To approximate the accelerations on an occupant you must
  • First perform a reconstruction of the accident the occupant was in
    • This can be a gross approximation or a detailed simulation, the detail depends on desired accuracy,
  • Next determine if the accelerations for the occupant location was different than the Center of Gravity (CG)
    • Occupants do not sit at the CG and sometimes depending on the impact configuration the accelerations at the occupant locations can be quite different from the CG, and
  • Lastly you need to determine the possible 'second collision' items of the occupant and the vehicle interior:
    • AFter the vehicles collide, the occupant(s) then interact with the vehicle sometimes referred to as the 'second collision'
      What vehicle components were struck by the occupant?
      how did the occupant interact with the belt? etc.

The following is a somewhat more detailed discussion:

• Before addressing the forces on the driver or other occupants you need to do a detailed collision reconstruction to determine the acceleration environment for the vehicle that the occupant(s) were traveling in.
  • Momentum and/or damage analysis programs can give you a first approximation however you should use a 3D simulation model, like msmac3D, to get a more detailed approximation of the acceleration environment for the entire collision interaction
    • Momentum and damage analysis programs assume instantaneous exchange of collision forces during the finite interaction of the colliding bodies and then require you approximate the duration and direction for the acceleration rather than actually calculate these items during the 50 to 150 millisecond collision like a 3D simulation program does.
    Next you need to determine the acceleration environment for where the occupant of interest was traveling.
    • Generally occupants do not travel at the Center of Gravity (CG), they are at locations other than the CG. And depending on where they are located and the impact configuration the actual acceleration environment they encounter may be quite different than the CG.
      For Determining accelerations/DeltaV for locations other than the CG you should review our paper RICSAC-97 - A Reevaluation of the Reference Set of Full Scale Crash Tests"
  • With the acceleration for the location of the occupant approximated then one needs to determine how the occupant interacted with the compartment and belts during the 'second collision' which occurs as the occupant collides or rides in the vehicle during the impact.
    • The vehicle reacts first and then the occupant reacts as it encounters the compartment components and the belts.
      Occupant simulation programs like ATB and MADYMO can be used to help understand the potentials for contacts and injuries however these are mainly research tools and have serious limitations due to the broad range of differences between occupants like that illustrated in the recent posting on BMI and due to all the required approximations required to run these occupant simulation programs as discussed in our ATB papers
      • For example:
        • The stiffness of components: there is no standardized protocol for determining the component stiffness, yield strength, etc. when used in occupant simulation programs and the values can affect results.
          • For example if you assume stiffer components you get higher G's, softer components, lower G's ,
        • the occupant parts which interact with the components:
          • you really can't take apart and measure arms and legs and musculature of occupants and the assumptions of how the occupants weight is distributed, how stiff or flexible are their joints, how you model their joints, etc. all can increase or decrease the resulting G's
        • active muscles -
          • all occupant simulation programs (ATB, MADYMO) are generally for passive occupants. Active muscles, movements due to occupant reations can act to or contribute to or reduce injuries
          • initial positions of the occupant, whether head turned or moving, arms, legs and torso may not be in the 'design' position
        • these and other items, discussed in our ATB papers are why occupant simulation programs are really research tools and may not be appropriate for individual case reconstructions except for understanding possible gross occupant movements

[MSI]

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).