Mercedes-Benz equips the S-Class with belt tensioners on the front seats and outer rear seats which in conjunction with the belt force limiters and airbags significantly reduce the forces acting on the occupants’ chest.

The belt force limiter is located inside the inertia reel and consists of a torsion bar which turns slowly when a force exceeding a pre-determined level acts on the belt strap, thereby producing a controlled reduction in the locking effect of the inertia reel. From a pre-specified point, the inertia-reel seatbelt slackens and the force exerted by the belt strap on the occupant is reduced.