Are the consequences the same at 20 km/h as at 50 km/h? Of course not. However, that doesn't mean the child restraint system hasn't been damaged. You need to remember that car seats are intended to protect children in the event of any kind of impact. They are designed for that, but what happens to the CSR itself? Should you get a new one?
The report entitled “The contribution of speed in preventing accidents in Spain” by Fundación MAPFRE reveals that approximately 400 lives would be saved each year if all drivers refrained from speeding. Speeding is the cause of over half of all collisions between vehicles entailing fatalities and of 44 percent of all collisions resulting in serious injuries. Speeding is intrinsically linked to the consequences of the accident and its severity. Seat belts and child restraint systems can reduce the effects of the accident by keeping us inside the vehicle and preventing us from hitting the car, other people or objects.
It's very difficult to determine how seriously a car seat has been damaged after braking sharply or if you're involved in a collision. There is often damage which is not visible to the naked eye: damage to the internal structure, the anchorage systems or the harness, or the plastic might be misshapen. If you continue to use the CRS your child won't be suitably protected and could be injured if you have to brake suddenly again.
You need to remember that if you're travelling at 60 km/h, inertia multiplies by 56 the weight of objects and people (a body which is slowing down will suffer inertia which propels it forward at a rate which is its weight multiplied by the value of the deceleration). Driving at 60 km/ is not excessive if you consider that in towns the speed limit can be 20-50 km/h. At that speed a child's weight is multiplied by 56. So if we're talking about an 18 month old child who weighs 12 kg, at that speed their weight increases to 672 Kg.
This also depends on whether we're talking about braking over distance or having to brake suddenly or a collision involving an object blocking our path. Here the consequences and the impact are greater as you're going from 50 km/h to zero in a milliseconds. Other factors at play are whether you've hit another vehicle from behind or whether you've been hit from behind. It all depends on the speed you're going and the type of accident. However, seat belts and child seats can be damaged nonetheless.
Many manufacturers recommend replacing the car seat if you're involved in an accident at over 10-20 km/h. In the Euro NCAP impact tests dummies representing children aged 6 to 10 were placed straight on the car seat or on a cushion. The impact tests are intended to ensure the safety of children travelling at 64 km/h but sometimes they don't factor in the state of the child seat after the accident.
Many child seat manufacturers also carry out their own impact tests on their products involving speeds of 30-50 km/h, although tests at 65 km/h are also often carried out. The dummies used in these tests suffer the same injuries your children will in the event of a collision. The dummies used are the closest in size and weight to the children in the age group being studied.
In the event of an impact, the safety belt loosens and stretches for a few seconds before retracting. The seat and its occupant are thrown forward momentarily before slowing down and coming to a halt. A rigid structure starts to slow down at the same time as the vehicle. So we can see here how the type of anchorage is as important as the car seat itself.
In any event, you're advised to check the state of the CRS after any collision or if you've had to brake suddenly. If you're in any doubt you should buy a new one. It's not worth taking risks when safety is at stake.