An actuation arrangement for a motor vehicle safety device

There is disclosed an actuation arrangement for a motor vehicle safety device such as a seat-belt pretensioning device. The actuation arrangement comprises an actuating piston for connection to the safety device, the piston being provided within a housing for movement relative to the housing from an initial position to an actuating position. The housing has an inlet configured for connection to a pressurized gas source for the supply of actuating gas to the housing to drive the piston towards said actuating position. The arrangement is configured to initially prevent movement of the piston towards the actuation position under the action of said actuating gas, and is characterised by the provision of a trigger means which is operable so as to act directly on the piston in a manner effective to permit said actuating gas to drive to piston towards said actuation position. In a preferred arrangement the inlet is arranged through the side of the housing and is occluded by the piston when the piston is located in said initial position. The trigger means can comprise a valve which is operable to direct a flow of triggering gas against the piston to move it out of the initial position and thus open the inlet for the flow of said actuating gas therethrough.