Case Study of Clothing Fabric Transfer to Seat Belt Webbing Under Accident Forces

Accident investigators are often required to determine if an occupant was wearing their seat belt during a collision. Previous studies have provided examples of physical evidence relied upon by investigators to determine if the seat belt assembly was subjected to occupant restraint loading. This paper examines the potential for clothing fibers to be permanently transferred to the seat belt webbing during a collision. To evaluate fabric transfer evidence as an indicator of restraint usage by an occupant during a collision, the following issues were examined: automotive seat belt webbing construction and behavior under load, fiber evidence found on the webbing in new and used conditions, and the transfer of different types of clothing fibers to webbing during full-scale sled testing. Our investigation suggests that, for the seat belt assemblies tested, certain clothing fibers may become permanently affixed or melted onto the webbing, but only under conditions that also produce load marks or telltales on the seat belt hardware indicative of occupant usage during a collision. No fibers were observed to be embedded or “caught” within the weave of the seat belt webbing, even when subjected to severe collision-type loading. This is consistent with the observed mechanics of webbing under load. This study was limited to one type of seat belt assembly and several types of clothing fabric. It is intended to be a methodology for evaluating potential fabric transfer to webbing in automotive collisions.