Marks on Seat Belt Systems with Pretensioners and Force Limiters in Airbag Deployment Crashes

Restraint system physical evidence is often examined during crash analysis to understand seat belt system use and effectiveness. As occupant restraint technologies have evolved over the years, the seat belt witness marks that occur in crashes have changed as well. Occupant loading has traditionally been the primary cause of marks on seat belt systems prior to pretensioners and force limiters. This research focused on newer seat belt systems equipped with force limiters and pretensioners, and how those features affect crash-induced witness marks.

The front seat occupant seat belt systems studied contained both retractor pretensioners and retractor torsion-type force limiters. The crashes that were analyzed occurred on U.S. roadways where at least one airbag deployed. Distinct marks were located on the retractor, D-ring, latch plate or webbing surfaces resulting from the activation of pretensioners and/or force limiters. The seat belt system marks from field crashes were compared to marks on components from laboratory crash-tested vehicles.