Seatback failure and collapse remain a danger to automobile occupants in real world rear-end collisions. Despite overwhelming evidence to the contrary, some automakers still like to refer to this collapse and failure event as “yielding” of the seat. They claim that the primary benefit of a seat that “yields” rearward in a rear-line-of-force impact is that the yielding or deformation of the seat structure is supposedly a method of energy absorption and “will” result in less force being applied to the seated occupant in a given crash. This design approach, however, has never been subjected to a rigid or proper engineering hazard analysis; it has never been quantified in terms of the amount of force reduction achieved by the “yielding” of the seat; and it has never been tested with human subjects under crash conditions. In addition, this supposed approach is not represented by a specific design but rather by the empirical result that when metal is deformed, energy is absorbed. The opposing view to this design approach is that simple, uncontrolled deformation of metal, such as what occurs when a seatback collapses, does not take into account the varying crash pulses, or the different weights of occupants, and has never been supported by any learned treatise on the study of human injury tolerance. Still, the proponents of the “yielding” approach argue that with yielding or deformation, there is a reduction of loading on the occupant’s neck and, therefore, an anticipated reduction in whiplash-type injuries in rear-line-of-force collisions. Many cars on the road today still have seats that the auto manufacturers contend were built in accordance with this “yielding” methodology.
A hazard analysis easily identifies the following hazards with a yielding/failing/collapsing seat or seatback:
- Loss of control of the vehicle
- Ramping rearward and impacting structure in the rear of the vehicle
- Ramping rearward and impacting occupants in the rear of the vehicle
- Ramping rearward and ejecting from the vehicle
- Loss of seat belt restraint system effectiveness
ALAN CANTOR, BSAE, of ARCCA Inc., is a nationally recognized vehicular crash expert and has been called upon by the US Congress and other organizations to offer opinions regarding occupant protection during crashes. He has also been involved in numerous design and study efforts on occupant crash protection issues for the National Highway Traffic Safety Administration, the U.S. Navy, the U.S. Army, and NASA.