*The following footage may be confronting. It features a crash test dummy undergoing a violent dynamic event.
In the video above, a child accessory harness (also known as 'H harnesses') is used in conjunction with a TNO P10 crash test dummy. The scariest part of this footage is that even though the dummy undergoes such a violent event (which would very likely have been fatal), this was classed as a 'Pass' under the 2010 version of the Australian Standard. In that standard, the accessory harness must keep the child restrained - in this video it achieves this by destroying abdominal soft tissues and literally hooking itself between the dummy's spinal cord and rib cage.
The way the dummy slides underneath the lap portion of the seatbelt is known as 'submarining' and can be deadly. Submarining of this nature can cause horrific internal injuries, and has tragically lead to the deaths of a number of children. While submarining can occur without the use of child accessory harness, the design of a child accessory harness is such that it makes submarining more prevalent when fitted or used incorrectly (which is reported to be as high as 100% of the time).
In 2009, a joint study on the efficacy of child accessory harnesses was carried out by members of the Prince of Wales Medical Research Institute and the New South Wales Centre for Road Safety.
The report concludes;
“Based on pelvic restraint, head excursion and abdominal injury potential, results from this study suggest that in frontal impact at least, accessory child safety harness systems provide no better protection than lap–shoulder belt systems. When accessory child safety harness systems are misused the level of protection provided is seriously degraded. Given the high frequencies of child safety harness system misuse seen in ﬁeld observation studies, and the fact that even when correctly used these system provide no improvement over a lap–shoulder belt, it seems likely that the risks of injury outweigh any perceived beneﬁt of a child safety harness system over a lap–shoulder system.”
We've also conducted our own comparative testing program, and we observed the same results as were published in the report – there was no increase in protection when an accessory child harness was used, compared to a standard lap-sash seatbelt, and in instances when the accessory child harness was not fitted correctly, the result was far, far worse. This testing resulted in InfaSecure discontinuing our child accessory harness, and modifying our booster seats to be incompatible with other brands of accessory harnesses.
Many Government and advocacy groups advise against their use unless the only available spot in the vehicle is a lap-only belt – and VicRoads go on to recommend parents consider having the lap-only belt replaced before resorting to using a child accessory harness.