Seat mounted airbag with force concentrator

An airbag system includes an airbag module 58 within a seat 16 having a pad 36, a seam 48 of a trim cover 24 of said seat being aligned with the airbag 70 so as to be ruptured by the inflating airbag and having force concentrating means 86 coupled to said seam to concentrate the force of the inflating airbag at the seam and so to ensure the rupturing of said seam. The force concentrating means may be at least one flexible non-elastic sheet (76, 78 fig 2) strong enough to withstand the force of the inflating airbag without tearing or a moulded plastic panel (110 fig 4). The force concentrator may be two flexible sheets (76, 78 fig 2) extending in opposite directions from the seam or a tubular sleeve 86 surrounding the airbag and having opposite ends joined to opposite sides of the seam. When the force concentrator comprises a panel it may have a weakened portion forming a break line (116 fig 4) and may be attached to the trim cover by hook and loop fastener strips (130 fig 4A), adhesive or adhesive tape. The flexible sheet may be woven nylon or airbag material and may be laminated with the seat trim or sewn to it.