ROOF CRUSH 4 .
INJURY MECHANISMS:
It might seem obvious that
roof crush is potentially harmful to motor vehicle occupants, but this has
actually been denied by the auto industry and the real reason it
is harmful is actually a little obscure. Most rollover injuries are not
related to crushing, most are impact injuries. That is, the injury results
from an occupant hitting something either inside or outside the
vehicle. As is always the case for impacts, the higher the
relative speed between the colliding objects, the more severe the impact.
Consider what might happen to you if you were riding in an open convertible and it rolled over. Your head could hit the ground with the speed of the vehicle.
The situation with s collapsing roof is similar. When the roof collapses, the occupant can be exposes to the linear –along the ground- velocity of the vehicle. This is because the roof is moving in toward the occupant instead of staying the same distance away as it was before the ground contact. If it moves inward, the velocity of the roof relative to the ground can approach zero. It might even be zero. Thus, anybody making contact with the collapsing roof can experience an impact like the occupant of the open convertible, essentially feeling the entire velocity of the vehicle with respect to the ground.
In this situation, with
the collapsing roof, the total velocity of the occupant with respect to
the ground is a combination of the linear velocity along the ground and the
rotational velocity (like the hand of a clock ) of the vehicle.
If instead, the roof does not collapse, the only velocity difference that the occupant can be exposed to inside the rolling vehicle is the rotational velocity of the vehicle plus the small changes that the intact vehicle experiences with ground contact. Thus, even while the occupant’s velocity is different from that of the part of the vehicle they happen to strike, the roof pillar for example, the resultant impact will still be less severe than the “ground “ impact they can experience with a collapsing roof.
Watch this VIDEO to get a clearer understanding of this. Note the differences in speed between the head approaching the roof rail and the head rebounding after the ground strike with the roof collapse. Notice also the displacement of the head and body as a result of the structural collapse. This displacement, which may be an important part of the mechanism of a spinal column injury, is only possible as a result of the roof crush.
See Also: "The Causes of Injury in Rollover Accidents."
