A safety arrangement (1) to provide protection for an occupant (2) in a motor vehicle includes a seat-belt (4) provided with a measuring device (8) to measure energy absorbed by the seat-belt. The measuring device may determine the length of safety-belt paid-out after a retractor (5) locks, the belt being paid-out against a force provided by a force-limiter (6). The energy absorbed is calculated and is used to control the vents of a ventable air-bag (15). The air-bag is vented if a substantial part of the energy of the occupant (2) 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.