Submarining occurs when the lap-belt, under load generated by the occupant, in a car collision slips up over the iliac crests and compresses the abdomen. The process has been found injurious if it occurs before the lab-belt force has dropped below 3kN. Most of the severe cases have been found in high violence crashes. By a series of sled tests followed by mathematical simulations of typical front seat and rear seat belt geometries and with a seat comprising of a homogenous cushion on a flat steel plate it has been shown that:​

• Occupants are more likely to submarine if the upper belt anchorage is far behind their shoulder (as in a rear seat or in a from seat in a two-door car).
• The closer to the seat the occupant’s feet are placed, the more likely submarining is to occur.
• Belt slack increases the risk of submarining.
• A pre-tensioner that operates on the buckle, signifi cantly reduces the risk of submarining.

It is also shown that the angle between the lap-belt and the pelvis, measured when the belt force has peaked and dropped to 3 kN, well can predict the risk of submarining.