The seatbelt is a primary and the most important passive safety device protecting occupants in all crash modes. The belt must work in harmony with other passive safety devices such as the frontal airbag, knee bolster and the seat to increase the level of occupant protection in a head-on crash. Failure of any component to restraint the occupant effectively in conjunction with the seatbelt can produce adverse occupant kinematics. Occupant submarining in a frontal crash is an occurrence when the belt moves from the desired stronger skeletal site and loads undesired anatomical location during the forward excursion of the occupant. The focal loading of the abdomen and ribs by the seatbelt produces abdominal and thorax severe injuries.

Subcutaneous fat appears typically darker on the radiographic film with an appropriate window. The focal loading from the seatbelt on the body tends to increase the density of the fat along the course of the seatbelt routing. The increase in the density of fat rises its attenuation and makes the fat appear lighter/whiter on the film. The change in the density, due to traumatic seatbelt loading, can be used in conjunction with other medical and physical evidence to demonstrate the occurrence of submarining. This type of analysis is also useful for the medical provider to take appropriate actions when the trauma patient first appears in the emergency department.

The purpose of this study is twofold:​ (1) to demonstrate the submarining detection techniques and methodologies using the NHTSA crash-test instrumentation data;​ and (2) to present real-world crashes as evidence of occupant submarining using fat-stranding analysis in conjunction with other medical and physical evidence.