A safety arrangement to provide protection for an occupant in a motor vehicle includes a seat-belt provided with a measuring device to measure energy absorbed by the seat-belt. The measuring device may determine the length of safety-belt paid-out after a retractor locks, the belt being paid-out against a force provided by a force-limiter. The energy absorbed is calculated and is used to control the vents of a ventable air-bag. The air-bag is vented if a substantial part of the energy of the occupant is absorbed by the seat-belt, but is not vented if a large proportion of the energy has not been absorbed by the seat-belt.