a self piercing cover assembly for concealing an air bag restraint system in a vehicle passenger compartment has a retractable cutter blade that is attached to the underside of an instrument panel next to front end of an invisible door beneath the instrument panel . when the air bag inflates , the cutter blade is pushed up by a deflector shield against the bias of springs and cuts through the instrument panel at several locations making it easier for the door to swing open . the deflector shield is then bent and broken off or deformed by the inflating air bag to provide a shield for protecting against contact with the sharp edges of the cutter blade . the shield and cutter blade retract under the action of the springs so that the shielded cutting edge is below the surface of the instrument panel to provide primary protection against contact with the sharp edges of the cutter blade after the air bag collapses .