A Q&A with Dr. Kelly Bosch
When air bags do not deploy in a vehicle accident, the question often arises quickly: Why not? For attorneys, claims professionals, manufacturers, and investigators, the answer is rarely simple. Air bag deployment decisions are driven by complex algorithms that consider crash severity, direction, timing, and occupant characteristics, all within milliseconds of impact.
We spoke with biomechanical engineer Dr. Kelly Bosch to explain how air bag systems work, why non-deployment can be appropriate, and how engineers evaluate whether an air bag should have deployed in a given crash. The discussion below addresses common questions and misconceptions surrounding air bag non-deployment and outlines the analytical methods used to evaluate these cases.
How do you help clients answer questions like “Why didn’t the air bag deploy in this accident?”
The science behind air bag deployments is very complex and multi-faceted. Vehicle manufacturers are challenged with balancing air bag deployments with injury mitigation for a wide range of scenarios. Air bags need to provide protection at varying impact speeds, force directions, and occupant sizes ranging from small females to large males. We also do not want air bags deploying when they are not needed; a rigorous matrix of testing for deployment and non-deployment scenarios is developed so that the algorithm can be tuned to discriminate between when an air bag is needed and when it is not.
There are many reasons an air bag may not have deployed: the accident may not have been severe enough, the location of impact with respect to vehicle structure may not trigger the deployment algorithm, or the occupant location within the vehicle may turn off the air bag deployment command, which can occur if an occupant is unbuckled and not fully engaged with the occupant classification system (OCS), for example.
Injury Biomechanics and Injury Consistency
How do investigators evaluate whether injuries could have been mitigated if an air bag had deployed?
Leveraging occupant kinematics analyses, exemplar crash tests, literature, and tools such as MAthematical DYnamic MOdeling (MADYMO), injury outcomes can be evaluated with and without the presence of air bags and seat belts. These analyses provide insight into whether injuries would have been lessened/avoided, unchanged, or increased if the airbags had deployed.
Occupant Kinematics and Biomechanics
Why is understanding occupant motion critical when evaluating air bag system performance?
Most crashes are in unique configurations with non-linear vehicle and occupant motions. In some cases, especially in older vehicles, occupant motions can cause an individual to unintentionally not properly loading an airbag, rendering them less effective in some instances. Understanding occupant kinematics provides information on the role of airbags in mitigating injury.
Accident Reconstruction and Crash Analysis
Why is accident reconstruction necessary in air bag non-deployment cases?
Accident reconstruction provides key information on the magnitude and direction of accelerations and forces imparted to the vehicle and the vehicle’s response to this loading. Without an understanding of the severity of the accident, the expectation for airbag deployment cannot be determined. Accident reconstruction and biomechanics also investigates the occupant’s role in the algorithm’s decision making, such as seat track positions, occupant size, and occupant location. Accident reconstruction also provides the foundations for understanding the occupants’ interactions within the vehicle.
How do delta-V and crash pulse influence air bag deployment?
The crash deceleration pulse and resulting delta-V provide key information to the ACM in determining if an airbag should deploy. The deceleration and rate of deceleration in the first few milliseconds of structural engagement are used to evaluate the severity of the accident before passive occupant restraint systems need to be commanded. The ACM also takes input from other sources such as door pressure sensors to determine if deployment is needed.
Common Misconceptions and Clarifications
Does air bag non-deployment automatically indicate a system defect?
No – an understanding of the severity of the accident combined with knowledge of the occupant including their size and positioning can help in determining the logic used in the decision. Accident reconstruction, review of EDR data, if available, and pulse severity analyses can also provide insight into whether or not a deployment would be expected. Each circumstance needs to be investigated and analyzed to understand if an airbag deployment would have been expected.
Are air bag deployment thresholds the same for all vehicles?
Definitely not. There are similarities between vehicles because of the occupant performance metrics within Federal Motor Vehicle Safety Standards (FMVSS) and general sensor misuse and abuse testing that defines the algorithms, but each vehicle has its own distinct algorithms. There are biomechanical gray zones inherent in each algorithm as well, where two outcomes can be possible, such as the cross-over between low output and high output deployments for frontal airbags, for example. We have ways to understand the general expectation of when an airbag should or should not deploy with advanced analysis techniques to understand borderline scenarios.
Value of a One-Stop Expert Approach
Why is a one-stop approach beneficial in air bag investigations?
Air bag investigations are generally multifaceted and require a holistic approach to understand the circumstances of the accident, resulting injuries, and airbag deployment logic. Funneling all of these questions through Rimkus consultants allows the analysis to flow between all aspects of the accident which provide insight into alternate causes of a non-deployment, such as an occupant that is out of position and unloading their occupant classification sensor.
Meet the Consulting Expert®
With significant experience in both the vehicle manufacturing industry and the United States government, Dr. Kelly Bosch is uniquely qualified to perform biomechanical investigations of vehicle accidents due to her deep understanding of vehicle design, safety systems, and human injury mechanisms in crash scenarios.
Contact Dr. Bosch to learn more about the Biomechanical Engineering and Transportation services that Rimkus can provide.
Kelly Bosch, Ph.D., P.E., ACTAR
Principal Consultant
+1 248 765 8128
[email protected]