Seat belts
Seat belts are there to keep a person safe. In many fatal crashes, un-restrained occupants died because they were flung out of their vehicles. Thereafter they may have hit an object outside or the vehicle rolled over them.
Airbags
Although airbags may be regarded as the best ever invention since the wheel, it is important to know that they work best in conjunction with a seat belt. Manufacturers also warn people about the importance of wearing a seat belt when a vehicle is equipped with airbags. If an unrestrained person flies forward at the same velocity the vehicle was travelling at prior to the crash and suddenly collides with a deploying airbag, it could result in serious or even fatal injuries.
Airbags deploy to full capacity in milliseconds (about 0.05 seconds). It is therefore vital to keep a child in a child restraint away from airbags in the front of a vehicle.
Forces during a crash
To answer this, we need to look at what happens when we sit in a moving vehicle. As the vehicle speeds up, our bodies travel at the same speed of that vehicle. If a vehicle pulls away with force, the occupants will feel the force pushing them back into their seat. The same happens when a vehicle severely reduces speed during heavy braking when the occupants feel a heavy forward force. This is the G-force. Astronauts experience a G-force of between 2- and 3G’s during take offs and when the rocket booster kicks in before leaving the earth’s atmosphere.
In a traffic situation the important side of this G-force comes into play when a vehicle suddenly decelerates, like during heavy braking or a crash.
Crash at 50 km/h
At a speed of 50km/h a vehicle travels at 13.88 meter per second. If this vehicle hits another solid object (like another vehicle) and forces the vehicle to a complete standstill in 0.3 seconds, the G-force will be 4.7G, nearly double what astronauts experience.
Crash at 100km/h
At 100km/h to a complete standstill in 0.4 seconds, the force will be a massive 9.4G’s! In a head on collision between two cars, both traveling at 100km/h, the G-force is 68G’s.
Now let’s take the example of the 50km/h crash at 4.7G. For this exercise we make the body weight of the occupant 70 kg. Multiply the 70 kilogram with the G-force (4.7) equals a 329 kilogram force that pushes forward. Just image what this will do to a baby that sits on someone’s lap at the time of a crash!
Rear passengers
Other things to consider are the false sense of safety when a passenger is unrestrained in the back seat. As we can see in the examples with the different speeds, even at a 50km/h crash, the rear passenger can push forward against the driver or the passenger with such heavy force, which may cause injury or even death. The seats are not designed to handle that much force. Heavier passengers will push forward at nearly 500 kg and that is only in a 50km/h crash!