Normalization and Scaling for Human Response Corridors and Development of Injury Risk Curves

To ‘collate’ impact response data from a group of samples from tests using unembalmed human cadavers (Post-Mortem Human Subjects, PMHS) for crashworthiness applications, it is important to transform the fundamental measured variable such as acceleration, force and deflection to a standard or reference, termed as normalization. Scaling can be defined as a process by which normalized data can be transformed from one Standard to another (example, mid-size adult male to large-male and small-size female adults, and pediatric populations). This chapter examines the pros and cons of approaches used in normalization/scaling processes for over four decades in impact biomechanics, with a focus on automotive applications. Specifically, the equal stress equal velocity and impulse momentum methods are discussed. The process of corridor development is critical to ensure that all anthropomorphic test devices mimic human impact responses. The chapter also examines methods used in developing human corridors, ranging from subjective to objective approaches in terms of incorporating individual variations or spread in the measured metrics. The variability in the response should also be taken into account in the determination of the human tolerance to impact, routinely used as a tool to improve occupant protection in crashes. Human tolerance can be expressed in terms of a human injury risk curve. The different empirical and statistical methods historically used in the biomechanical field to develop injury risk curves are presented in this chapter. The normalization group ISO/TC22/SC12/WG6 recommended a procedure to construct injury risk curves aiming at harmonizing the development of injury risk curves. This procedure is presented in detail. It includes several steps taking into account the specific censored status of the biomechanical data and including some checks related to the statistical modeling of the injury risk. Topics allowing future improvement of the procedure are discussed.