Five-point harnesses are the most effective fastening systems for cars in that they are able, in the event of a crash, to prevent the body being thrown in almost any direction: forwards, sideways and upwards, as well as avoiding the submarining effect. This is the type of harness used in competition vehicles and, of course, in child seats up to the current Group I.
A beneficial consequence of these five anchor points for a CRS up to Group I is that they protect the child's abdominal area, whereas a three-point seat belt, used to anchor a CRS from Group II upwards, offers less protection in this respect. It is a susceptible area in a collision if the child's posture is not correct when traveling in the car, something that happens frequently with nearly all children.
Objective: reduce the probabilities of children sustaining abdominal injuries
To avoid or reduce the risk of child abdominal injuries in the event of a collision, there are different solutions ranging from the child's posture and the CRS used. The simplest one is for the Group 2/3 booster seat to be equipped with a low guide to keep the lap belt in an optimum position.
Another more involved and, a priori, more effective solution is for the CRS itself to have a fourth anchor point that will assist in keeping the lap belt in place and contribute to reducing the forces applied to the abdomen in the event of a crash. As with five-point harnesses, this central piece eliminates the submarining effect and avoids the belt slipping up over the belly, keeping it the lower abdomen area.
The child restraint system manufacturer Britax Römer has developed SecureGuard, patent pending technology that restricts any undesired movement of the lap belt. This method implies having to pass the lap belt through the central piece when positioning the child in the seat.
The extent of abdominal injuries varies according to the posture adopted and the correct positioning of the seat belt. In cases where the lower strap of the seat belt is positioned above the belly, these injuries can affect the liver, spleen or kidneys, and this is more likely when the child is sleeping and not aware of its own posture.
All this could be improved by using a five-point harness. The problem is that safely restraining a body weighing 15 to 18 kilos implies the need to use extremely resistant harnesses and supports capable of holding the whole system in place in the event of a crash. This is why it is recommended that any child weighing more than 18 kilos should use a CRS suited to their physical characteristics held in place by the car's seat belts.