The Impact of Seat Belt Pretensioner Deployment on Forward-Leaning Occupants

Abstract

Pyrotechnic seat belt pretensioners typically remove 8–15 cm of belt slack and help couple an occupant to the seat. Our study investigated pretensioner deployment on forward-leaning, live volunteers. The forward-leaning position was chosen because research indicates that passengers frequently depart from a standard sitting position. Characteristics of the 3D kinematics of forward-leaning volunteers following pretensioner deployment determines if body size is correlated with subject response. Nine adult subjects (three female), ages 18–43 years old, across a wide range of body sizes (50–120 kg) were tested. The age was limited to young, active adults as pyrotechnic pretensioners can deliver a notable force to the trunk. Subjects assumed a forward-leaning position, with 26 cm between C7 and the headrest, in a laboratory setting that replicated the passenger seat of a vehicle. At an unexpected time, the pretensioner was deployed. 3D kinematics were measured through a nine-camera motion capture system with reflective markers on the left and right glabella, tragus, manubrium, C7, lateral proximal head of humerus, olecranon process, patella, and lateral malleolus. For uniformity, all pretensioners were of the same model made by Autoliv and were dual systems (having deployment in the retractor and outbound anchor). The initial velocity of the trunk (first 50 ms) was dependent on the body size, with smaller subjects getting pulled back quicker. Following the first ~160 ms, there was a slight rebound where subjects briefly moved forward, followed by a period of high intersubject variance in movement. By isolating the effects of pyrotechnic pretensioner deployment on live volunteers, this study fills in an important gap in automotive safety research and may help with evaluating computer models or designing future restraint systems with advanced sensor technology where pretensioners deploy prior to significant vehicle deceleration.