Abstract: A vehicle subject to high level and low level impact conditions includes an occupant restraint cushion which is inflated at a relatively high rate under high impact conditions and at a relatively low rate under low level impact conditions. The inflator for the cushion includes a pressure vessel containing pressurized stored gas and a combustion chamber containing a propellant. Under low level impact conditions, the propellant is ignited and the resultant gases flow through a fluted orifice into the pressure vessel and then flow with the stored gas to the cushion. The area of the orifice controls the flow rate of the resultant gases out of the combustion chamber to control the pressure within the chamber and the burn rate. Under high level impact conditions, a ball within the combustion chamber is explosively fired into the orifice to restrict the flow area of the orifice. This increases the pressure within the combustion chamber to increase the burn rate and the flow rate to the cushion.