Dummy Limitations

Pediatric crash dummies are designed to have the dimensions of an average child of the age they represent, primarily based on a 1977 study of child anthropometry (Snyder et al. 2007). Their overall weight matches the average child weight from this study as well, but the distribution of weight among body segments is scaled from the distribution found in adults. The response to loading of child dummies is also scaled down from adult dummies with limited adjustment made for changes in mass and stiffness (Irwin and Mertz 1997). The responses of adult dummies are primarily based on testing of elderly cadavers under dynamic loading conditions. Most pediatric dummies are designed for frontal impact loading, although some versions are designed for side impact testing.

Results from testing using crash dummies must be viewed within the limitations of the data from which they were developed. On the one hand, child crash dummies have been used to develop the safest restraints available. On the other hand, child dummies do not sit the way children do, have limited amounts of sensors/ instrumentation, and have idiosyncrasies that can affect test results (Ash et al. 2009). When neck loads have been measured in child dummies seated in restraint systems, they often reach alarming levels relative to estimates of neck injury thresholds based on scaling adult values (Park et al. 2011, Menon et al. 2005). Given that serious neck injury to properly restrained children is rare, neck injury-related measurements need to be reviewed with caution. The design of the child dummy’s spine only has flexible components in the neck and lumbar, not the thoracic region, which may be leading to more bending and higher loading in the neck than a real child with a fully flexible spine would experience (Seacrist et al. 2010).

Another example is that standard child dummies cannot currently measure abdominal loading, which is one of the more common body regions injured in older children not using boosters. The movement of the dummy during dynamic testing must be reviewed as well as the values from instrumentation, and both must consider the limitations of the dummy and instrumentation. Design of good child restraints must balance test results with field data and judgment.