Abstract
Legislation in Europe requires children younger than 12 or shorter than 150cm to use a child restraint system (CRS) when travelling in motor vehicles. These have decreased the number of children fatalities in car accidents, yet certain body regions such as the abdomen are still prone to severe trauma. One of the mechanisms by which injuries to this body region occur is called "submarining". It involves the seat-belt slipping over the pelvis onto the abdomen during rapid deceleration, therefore afflicting the abdomen with injurious loads. The motion characterising submarining with CRS is as of yet poorly defined, and although CRS are assessed for protection level, there is currently no established identification criteria for submarining. As part of the Enabling Protection for Older Children project (EPOCh), standard frontal impact sled tests of 10 CRS (6 high back booster seats; 4 booster cushions) with 10 year old anthropomorphic testing devices (ATDs) were analysed qualitatively, transversally and longitudinally for submarining detection. The methods used included video analysis, descriptive and inferential statistics, principal component analysis, time series analysis, as well as multiple linear regression and logistic regression, applied on both ATD trajectories and ATD instrumentation recordings (dynamic data). From the videos, trajectories and dynamic data, submarining motion is shown to embody an exaggerated slouching movement regardless of the CRS type. The observations and quantitative results confirm that exaggerated forward knee displacement is characteristic of submarining, as well as a very strong criterion for the latter's detection. No other individual trajectory or dynamic variable distinguish clear submarining behaviour, however the regression analyses on dynamic variables establish the association of the pelvis, lumbar and chest as representative of the knee displacement, and demonstrate the combination's capacity to distinguish submarining cases. These findings establish the complexity of the movement involved in submarining and the potential of using current ATD instrumentation for its assessment with CRS. This opens a path for an integral approach to ATD movement in CRS appraisal and suggests considering pelvis, lumbar and chest motion control for submarining prevention.