The characteristics of collision-induced markings generated on seat belt systems are not solely dependent on the belted status of the occupant, but also the technological features incorporated in the seat belt assembly. Pretensioner deployment can leave physical evidence on restraint system hardware and webbing in the absence of occupant loading and may be misinterpreted as evidence of seat belt use.
The presence of physical evidence on restraint system hardware and webbing is inadequate to conclude that a seat belt restraint was in use. Careful consideration of restraint system physical evidence combined with restraint system geometry and incorporated technological features can distinguish physical evidence related to seat belt use or non-use during a collision event.
Gregg R. and Petroskey K. Assessment of Collision Markings on Non-Used Vehicle Restraint Systems. Society of Automotive Engineers. SAE 2020-01-0975.