Evaluation of devices to improve shoulder belt fit.

Sullivan, Lisa K.; Chambers, Fletcher K. · 1994 · ROSA P / United States. Department of Transportation. National Highway Traffic Safety Administration

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Summary

This study evaluates the safety performance of three commercially available shoulder belt fit devices—Child-Safer™, SafeFit™, and Seatbelt Adjuster™—designed to reposition lap/shoulder belts for improved comfort. Conducted by the National Highway Traffic Safety Administration (NHTSA), the research addresses concerns that these unregulated devices might inadvertently increase injury risk during crashes. The study utilized 35 dynamic HYGE sled tests employing FMVSS No. 213 test pulses and seat fixtures. Tests were performed using 3-year-old and 6-year-old child dummies, as well as 5th-percentile female and 50th-percentile male adult dummies. Impact orientations included standard frontal, 15° clockwise oblique, and 15° counterclockwise oblique. Baseline tests without devices were conducted for comparison, and one test evaluated the Child-Safer™ in conjunction with a belt-positioning booster seat. The results indicated that the devices frequently failed to meet FMVSS No. 213 injury criteria, particularly for smaller occupants. Head Injury Criterion (HIC) values exceeded the 1000 limit in 5 of 8 tests with the 3-year-old dummy and in 5 of 12 tests with the 5th-percentile female dummy. Specifically, the Child-Safer™ and SafeFit™ devices consistently produced high HIC values for the 3-year-old and 5th-percentile female dummies across multiple orientations. Chest acceleration limits (60 g’s) were exceeded in two tests with the 6-year-old dummy using the Child-Safer™ and in one test with the 3-year-old dummy using the SafeFit™. When the Child-Safer™ was used with a booster seat, the 3-year-old dummy recorded a HIC of 1575 and chest acceleration of 61.6 g’s, significantly higher than the booster-only baseline (HIC 906, 48.8 g’s). Kinematic analysis revealed that the devices altered occupant motion in ways that increased injury risk. The Child-Safer™ allowed approximately 51 mm of webbing to release during impact, causing significant forward torso rotation in the 3-year-old dummy. All three devices contributed to "roll-out," where the dummy’s torso slipped out from under the shoulder belt, particularly in oblique impacts. For the 5th-percentile female dummy, the SafeFit™ delayed submarining until later in the crash event, while the Child-Safer™ increased neck loads and moments by up to 51.5% and 83%, respectively, compared to baseline conditions. The study concludes that these belt fit devices do not improve safety and may significantly increase the risk of head, chest, and neck injuries, especially for children and small adults. The devices altered belt geometry and occupant kinematics in detrimental ways, such as allowing excessive torso rotation or delaying proper belt positioning. NHTSA determined that the devices failed to provide the intended safety benefits and posed potential hazards, highlighting the need for regulatory scrutiny of aftermarket restraint accessories.

Key finding

The use of Child-Safer, SafeFit, and Seatbelt Adjuster devices resulted in Head Injury Criterion values exceeding 1000 in multiple test configurations for 3-year-old and 5th percentile female dummies, indicating increased head injury risk compared to baseline conditions.

Methodology

simulator

Sample size: 35

Provenance

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Topics

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• seat belt use