ESTABLISHING LUMBAR INJURY TOLERANCE FOR ENERGY ABSORBING SEATS CRITERIA AND TESTING LIMITATIONS

This paper deals with the criteria used to assess energy absorbing seat performance. It does not deal with physiological aspects of human tolerance. It identifies the current approaches for establishing whether energy absorbing seats limit the axial loads imposed on an occupant’s spine (Z axis) to tolerable levels, emphasizes the differences in current criteria, and discusses some of the inadequacies in both the criteria and test devices. It presents a summary of the backgrounds for the current approaches, and mentions a few of the questions inherent in the approaches. Inadequacies in current anthropomorphic dummies (ATDs) currently used to evaluate the energy absorption systems are discussed. The paper then describes the approach used in a previous study referred to as the Advanced Energy Absorber (AEA) study that led to recommended tolerances that are believed to be too high. The approach used in the AEA study is expanded upon and an approach is developed that expresses tolerance in a manner that could be insensitive to variations in the weight of the ATD. The tolerance is expressed as a factor that when multiplied by the weight of the nude torso (weight of the nude portion of the ATD supported by the lumbar load cell) of the ATD yields the maximum tolerable lumbar load that should not be exceeded in the specified test. This paper suggests a specific value for the basic multiplier. An approach is recommended for current use that is based on current capability. Suggestions are made for future development that would improve the ability to not only assess the capability of energy absorbing systems, but also to enable optimization of the capability of the systems. It suggests that a single criterion needs to be chosen and standardized to enable comparable products and levels of protection to be provided to the occupants of the many crashworthy seats now being offered. It also recommends that a family of ATDs be developed that more closely replicates the weight distribution of humans and that is capable of reproducing the response of humans, and each other, when impulsively loaded in the Z direction.