Evaluation of Seat Belt Assembly Physical Evidence in Properly Functioning and Intentionally Disabled Retractor Demonstrations

For more than 30 years, field research and laboratory testing have consistently demonstrated that properly wearing a seat belt dramatically reduces the risk of occupant death or serious injury in motor vehicle crashes. The emergency-locking portions of seat belt retractors are critical components that engage as a result of vehicle deceleration and lock the retractor as webbing is withdrawn during the onset of occupant loading. The field performance of emergency-locking retractors (ELRs) is commonly called into question. Recent studies have raised concerns about the effectiveness of retractor locking mechanisms in multi-planar collisions, including rollovers. Investigators of vehicle crashes would benefit from samples of diagnostic physical evidence which could be used to assist in distinguishing between an unrestrained occupant, a properly restrained occupant and a restrained occupant where the ELR mechanism was disabled in a crash environment and allowed webbing to “spool-out”.

This study investigates and compares the physical evidence created on seat belt assemblies in various crash modes with properly functioning ELRs and intentionally disabled ELRs. This is accomplished through the analysis of sled and vehicle drop demonstrations in which the ELR was properly functioning and intentionally disabled. Results of these demonstrations indicate that physical evidence on restraint system hardware is likely to be created on the D-ring, latch plate and/or webbing load surface in both properly functioning and intentionally disabled retractor scenarios. The restraint system physical evidence from these demonstrations provides a useful diagnostic tool for evaluating proper ELR performance or alleged improper ELR performance. If “spool-out” were to occur during collisions, physical evidence would be expected and lack there-of is not evidence of restraint malfunction. Finally, the presence of polymer flow on latch plate or D-ring abrasions is not sufficient to indicate that a retractor malfunction occurred, however, it does appear to be a necessary condition.