An air bag safety system for cushioning restraint of a vehicle occupant during an impact event, the safety system comprising: a variable depth inflatable air bag cushion (20, 120, 220, 220') adapted to be inflatable to one of a first depth and at least a second depth greater than the first depth, wherein the air bag cushion (20, 120, 220, 220') includes at least one vent opening (64, 164, 264, 264'); and a displaceable vent blocking cover element (63, 163, 263, 263') of substantially pliable material supported at a surface of the air bag cushion (20, 120, 220, 220') and disposed in opposing relation to said at least one vent opening (64, 164, 264, 264'), wherein the cover element (63, 163, 263, 263') is adjustable from a first operative position relative to the vent opening (64, 164, 264, 264') when the air bag cushion (20, 120, 220, 220') is inflated to said first depth and to a second different operative position relative to the vent opening when the air bag cushion is inflated to said second depth so as to vary emission of inflation gas through said at least one vent opening (64, 164, 264, 264') in a predefined manner based upon the depth of inflation of the air bag cushion (20, 120, 220, 220'), characterized in that the cover element (63, 163, 263, 263') is operatively attached to at least one elongate tensioning strap (71, 171, 271, 271') extending between the cover element (63,163, 263, 263') and a shape defining tethering element (30, 130, 230, 230') operatively connected to a surface of the air bag cushion (20, 120, 220, 220') and to a releasable attachment mechanism, such that the airbag cushion is selectively inflatable to the first depth or the second depth. a variable depth inflatable air bag cushion (20, 120, 220, 220') adapted to be inflatable to one of a first depth and at least a second depth greater than the first depth, wherein the air bag cushion (20, 120, 220, 220') includes at least one vent opening (64, 164, 264, 264'); and a displaceable vent blocking cover element (63, 163, 263, 263') of substantially pliable material supported at a surface of the air bag cushion (20, 120, 220, 220') and disposed in opposing relation to said at least one vent opening (64, 164, 264, 264'), wherein the cover element (63, 163, 263, 263') is adjustable from a first operative position relative to the vent opening (64, 164, 264, 264') when the air bag cushion (20, 120, 220, 220') is inflated to said first depth and to a second different operative position relative to the vent opening when the air bag cushion is inflated to said second depth so as to vary emission of inflation gas through said at least one vent opening (64, 164, 264, 264') in a predefined manner based upon the depth of inflation of the air bag cushion (20, 120, 220, 220'), characterized in that the cover element (63, 163, 263, 263') is operatively attached to at least one elongate tensioning strap (71, 171, 271, 271') extending between the cover element (63,163, 263, 263') and a shape defining tethering element (30, 130, 230, 230') operatively connected to a surface of the air bag cushion (20, 120, 220, 220') and to a releasable attachment mechanism, such that the airbag cushion is selectively inflatable to the first depth or the second depth.