Thoracic injury metrics with side air bag: stationary and dynamic occupants

Abstract

Objective: Injury risk from side air bag deployment has been assessed using stationary out-of-position occupant test protocols. However, stationary conditions may not always represent real-world environments. Therefore, the objective of the present study was to evaluate the effects of torso side air bag deployment on close-proximity occupants, comparing a stationary test protocol with dynamic sled conditions.

Methods: Chest compression and viscous metrics were quantified from sled tests utilizing postmortem human specimens (PMHS) and computational simulations with 3 boundary conditions: rigid wall, ideal air bag interaction, and close-proximity air bag deployment. PMHS metrics were quantified from chestband contour reconstructions. The parametric effect of DeltaV on close-proximity occupants was examined with the computational model.

Results: PMHS injuries suggested that close-proximity occupants may sustain visceral trauma, which was not observed in occupants subjected to rigid wall or ideal air bag boundary conditions. Peak injury metrics were also elevated with close-proximity occupants relative to other boundary conditions. The computational model indicated decreasing influence of air bag on compression metrics with increasing DeltaV. Air bag influence on viscous metric was greatest with close-proximity occupants at DeltaV = 7.0 m/s, at which the response magnitude was greater than linear summation of metrics resulting from rigid impact and stationary close-proximity interaction.

Conclusions: These results suggest that stationary close-proximity occupants may not represent the only scenario of side air bag deployment harmful to the thoraco-abdominal region. The sensitivity of the viscous metric and implications for visceral trauma are also discussed.

Fig. 1

Model and sled environment

Fig. 2

Occupant model with thorax contours at four levels

Fig. 3

Chest contours reconstructed from (a) chestband measurements and (b) computational model. Contours are shown undeformed, at instant of maximum deflection, and at two intermediate times. Open circle indicates deflection computation points.

Fig. 4

Aggregate injury metric response from rigid wall boundary condition at the eighth rib level from PMHS (ΔV = 6.7 ± 0.3 m/s) and computational occupant models (ΔV = 6.0 and 7.0 m/s): (a) chest compression, (b) deflection velocity, and (c) viscous metric

Fig. 5

Biomechanical response in time domain from simulation of stationary close-proximity occupant as measured by the (a) compression and (b) viscous metric at the four thoracic levels

Fig. 6

Peak thoracic biomechanical response from simulations in stationary scenario and at all ΔV as measured by the (a) compression metric and (b) viscous metric

Fig. 7

Simulation thoracic peak biomechanical response to ΔV with and without SAB measured by the (a) compression metric and (b) viscous metric. Numerical values indicate metric increase induced by close-proximity boundary condition relative to rigid contact.

Fig. 8

Normalized metric response to close-proximity airbag, i.e., rigid metric subtracted from close-proximity metric