A safety arrangement for use in a motor vehicle comprises at least one plastically-deformable element, defining an interior chamber, which will deform only when subjected to at least a first predetermined force. A source of gas is connected to inject gas into the chamber and a signal generator is provided to generate a signal representative of crash severity which is to be applied to the element during a crash situation or in an anticipated crash situation. The signal generator is connected to a control unit so as to provide the control unit with the signal. The control unit is connected to the source of gas in order to control the source of gas and to inject gas into the interior chamber of the deformable element so as to increase the gas pressure in the chamber when the crash severity signal is substantially in excess of a predetermined threshold. The arrangement provides a structure whose energy absorption characteristics can be varied according to the severity of a crash situation.