We know child seats are important, but do we know why? How do they work to keep our children safer in a car accident, and why is it so vitally important that they be installed correctly?
It helps to first examine how seat belts work. There’s an old saying in injury analysis — “it’s not how fast you’re going, but how fast you stop,” meaning injuries occur not because you are traveling fast, but because you stop incredibly quickly (like under a tenth of a second). To give an obvious example of this, a passenger jet lands at something like 150 mph, and everyone is fine because it comes to a stop over a relatively long period of time. If that same jet crashes into the ground at the same speed, everyone dies instantly. The difference is the time period over which the plane stops.
So let’s apply this to seat belts and child safety seats. Let’s say John runs his car into a wall at 50 mph, and is stupid
enough to not be wearing a seat belt. John’s car stops in the blink of
an eye, but poor John keeps moving at 50 mph . . . until he hits the
windshield with his head (for all of you smart alecks out there – his
car didn’t have an airbag). John has bought himself a ticket to the
morgue, because his skull couldn’t withstand those forces.
Obviously, one thing a seat belt would have done is keep John from striking the interior of the vehicle. But another, less obvious, benefit of a seat belt is that it would have coupled John to the vehicle and allowed him to “ride down” the forces of the crash. Vehicles today are designed with crumple zones which are designed to collapse and absorb the energy from a collision, thereby lessening the forces on the occupants. Ideally, the occupant compartment is designed like a cage, and minimizes intrusion from other parts of the vehicle. As long as an occupant is wearing a seat belt correctly, he will gain the benefit of the cars crumple zones absorbing energy, and, like a jet landing, he will be able to ride down the accident forces over a longer period.
The seat belt retractor is designed to make sure the belt is snug to an occupant’s body at all times. During normal movement of a passenger, it allows a person to move freely, but in an accident, or with a sudden stop, it locks quickly. It’s important that the retractor lock quickly. Let’s use the example of a 50 mph crash. If the retractor doesn’t lock at the moment of impact, the occupant keeps moving at 50 mph. When the retractor locks too late, there are tremendous forces put on the person as he slams into the belt. An analogy would be the snapping of a whip.
This is why it’s so important to install child carseats correctly. If a carseat is tightly coupled to the vehicle, via a seatbelt or “latch” system, and also a tether, then an infant or child will gain the benefit of the vehicle absorbing most of the accident forces — the forces to the child are lessened. If the car seat is not tightly coupled, the child is going to keep moving forward at the vehicle’s speed. Two things can happen – both of them bad. 1) The child can move forward so far that he strikes a component of the vehicles interior, and, 2) when the retractor does finally catch the seat, tremendous forces are put on the child’s head and neck as he is snapped violently.
So, that’s a quick lessen in seat belt safety, and why it’s so important to install car seats correctly. In my next posts, we’ll talk about how to install them so that your child is as safe as possible when he or she is riding in a car.
Most people have no idea how violent a high speed crash is. If you’d like to see the forces involved on a child, click here to see a video of testing done on a child accident dummy. As you’ll see, it’s still incredibly violent. Keep in mind that this is slow motion — everything you see takes place in the blink of an eye.
If anyone ever questions the importance of a car seat, or jokes about how they didn’t have them when they were kids, and they turned out fine, show them this video comparing a child in a car seat to one who’s unrestrained.