One of the biggest problems in protecting occupants is keeping them in the proper position. For example if the driver’s lower body slides under the seat belt, not only will his knees crash into the dash, but his head and face become lower in the seat. With the airbag deploying at the angle of the steering wheel, this put his face much closer to the bottom of the deploying airbag, endangering him of being hit. Also by his face not landing in the center of the bag, the distribution of impact over a lager area is defeated, therefore not properly cushioning him from the impact.    

Manufacturers have developed many devices to stop this submarining effect and are in the process of developing many others. 

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Knee Bolsters or Knee Airbags

Knee airbags or bolsters were some of the first of these devices to be developed and are still the most commonly used. These devices are actually multi purpose, they not only stop the submarining effect, holding the occupant in place but, they also protect against leg and hip injuries. Though many manufacturers used heavy padding on their lower dashes for years, in a sever crash occupants still sustained major leg and hip injuries from their knees hitting the dash.

 Knee Bolster

The airbag extends out from the dash approximately 5 inches when fully inflated. The deployment of the bag pushes a bolster or padded panel against the occupant's lower legs, contacting them at approximately the knee cap level and cushioning the legs down to approximately the shin and ankle area. This in turn distributes the forces over the lower legs rather than the femur and at the same time holds the occupant properly positioned in the seat.

The first knee airbag in the US came out on the 1996 model Kia Sportage and was only offered on the driver’s side. Today many are standard equipment on both the driver’s and passenger’s side. These systems use an airbag attached to the back of the lower dash panel, under the steering column or clove box.

Carpet Airbags

These airbags are mounted under the carpet; they are deployed by a stored gas inflator mounted over the center tunnel and like the knee bolster they are actuated by the same sensors as the frontal airbag, but at a faster rate.

Also like the knee bolster they are multi purpose, providing cushioning for the occupant’s feet and with the upward motion on the legs they are holding the occupant’s lower body in the proper position in the seat.

These work in conjunction with another airbag mounted under the driver’s seat, that when inflated tilts the seat back. By tilting the seat back and the upward motion to the legs, the lower body is held in place and the upper body is moved further away from the deploying frontal airbag.

1.  A gas generator inflates the metallic envelope compressing the foam of the cushion up in the front portion of the seat, pushing the occupant back against the back rest, as the side foam forms around the pelvis.

2.  A deflation controller, situated beneath the module, then allows the metallic envelope to slowly deflate and the metal to deform to assume the shape of the occupant’s pelvis. This forms like a pocket in the seat to hold the occupant in position and a protective shield around the pelvic area to prevent injuries. It also lifts the weight of the legs, preventing the downward force of the feet pushing into the floor.

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