Friday, July 15, 2011

Car seat safety part 1: Why rear-facing?

Last week, I actually started toying with the idea of turning Josh forward-facing in the car.  He's about 22 pounds, I reasoned.  And, basically, he hates the car seat, hates not being able to see Mom, and the whole thing is really a struggle.
And then I was rear-ended by a truck.

In a rear end collision, the force of the impact travels through the car.  Newton's first law of motion, An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an external force, comes into play here.  Most rear end collisions happen when vehicle one is stopped, whether at  red light, stop signing, turning, or what have you. So you have vehicle 1, at rest, with its passengers inside, also at rest.  Vehicle 2 comes along, strikes vehicle 1(vehicle 2 is your external force here), causing it to move forward.  A properly seatbelted passenger's hips and torso will move forward to the vehicle, but the unrestrained head and neck stay where they are, and are pushed back into the headrest(and you thought headrests were just for comfort).  The neck muscles, however, hold the head to the torso, suddenly "whipping" the head forward.  The head keeps moving until it is ahead of the torso, and those same neck muscles will then catch and stop the head from moving, bringing it back level with the torso.
Thus your poor, unfortunate occupant now has whiplash.

What does this have to do with car seats?

Babies are born with weak neck muscles.  Though they generally strengthen greatly by 6 months, the sheer mass of the head in proportion to a baby or todder's body is still much greater.  To put it in perspective, the mass of a baby's head is 25% of the body, compared to 6% of an adults.  A forward-facing car seat puts an extreme strain on the baby's neck, which has to hold that large head back in the event of a crash.  Those neck muscles are doing everyting the adult's neck muscle are doing in the scenario I described, but are responsible for a much, much larger mass proportionally.  A baby or toddler's neck sustains an incredible amount of force in a crash, stretching, stressing, and possible even fracturing the spinal cord.  In a forward facing car seat, the child's body, restrained by the straps, is held in place while the head is thrown forward. A rear-facing car seat, however, keeps the head, neck and spine fully aligned while in a crash.  The head is not thrown forward, but is held firmly in place.  The child is able to "ride down" the crash, as the car seat itself takes the brunt of the force(this is why you must get a new car seat after an accident, and do not ever use a used car seat unless you are sure it has never been in a car crash). 


  (University of Michigan Child Passenger Protection)

See the difference?  Same seat, same car seat, same size child dummy, same force applied--the only difference is how the car seat is located.

And this is why Joshua will remain rear-facing in the car for quite some time.


This is part 1 of my summer series on safety while traveling with children. Next week I will be talking about making sure your car seat is safe and properly installed, as well as some hints on choosing a good car seat.

1 comments:

Life More Simply said...

Thanks for the great post--let me know if I could re-post this on my blog, linking to your blog!