Knee Airbag Supplemental Restraint Systems

SUBJECT: Knee Airbag Supplemental Restraint Systems TOPIC: Knee Airbag 2004 Model Year Update OBJECTIVE: Identify the various designs, locations, and function of knee airbag systems available in vehicles...


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SUBJECT: Knee Airbag Supplemental Restraint Systems
TOPIC: Knee Airbag 2004 Model Year Update
OBJECTIVE: Identify the various designs, locations, and function of knee airbag systems available in vehicles.
TASK: Given pictures of the interior of vehicles, identify the location of the knee airbag, explain its operating features, and describe responder safety considerations for operating near an undeployed knee airbag system.

Currently, 10 models of vehicles sold in the United States are equipped with driver’s knee airbag systems or with dual, driver and front passenger knee airbags. According to one U.S.-based airbag manufacturer, 3 million model year 2004 vehicles will be produced with “inflatable knee bolsters” (see it here).

U.S. Automobile Knee Airbag Systems
Audi A8
(Driver/passenger knee bags)
10 bags total
Model year 2004

BMW 645
(Driver/passenger knee bags)
8 bags total
Model year 2004

Lexus LS 430 sedan
(Driver/passenger knee bags)
8 bags total
Model year 2004

BMW 760
(Driver/passenger knee bags)
8 bags total
Model year 2004

BMW 745
(Driver/passenger knee bags)
12 bags total in vehicle
Model year 2004


BMW Z4 convertible
(Driver/passenger knee bags)
8 bags total in vehicle
Model year 2004
(Also contains side-impact airbags in rear quarter panels of this convertible)

Chrysler Pacifica
Model year 2003
Inflatable knee blocker
for the driver only

Kia Sportage
(Driver only)
3 bags total
Model years 1996-2001

Lexus RX 330 SUV
(Driver knee bag only)
7 bags total
Model year 2004

Mercedes SL-Class SL55
(Driver knee bag only)
5 bags total in vehicle
Model year 2004

Researchers report that hip injuries accounted for 48% of car-crash leg injuries in 1993-2001 vehicles (see “Knee Protection May Cause Worse Hip Injuries” by Jayne O’Donnell and James R. Healey, USA Today, May 18, 2003). To address this injury concern and to help keep front-seat occupants away from frontal airbag inflation zones, manufacturers have dramatically increased their use of knee airbag systems in 2004 model year vehicles.

Knee airbags are installed relatively low along the instrument panel, below the glove compartment on the passenger’s side of the dash. On the driver’s side, the knee airbag is positioned beneath the steering column. This relatively new technology works simultaneously with seatbelts and pre-tensioners to improve overall occupant survival in a frontal collision. In a frontal collision that initiates deployment of one or both frontal airbags, knee airbags deploy outward from the dash toward the front edge of the seat.

There are two basic knee airbag designs. One style uses the inflated knee airbag itself to press against the knees of the front occupants. The other knee airbag design has a “knee bolster” panel permanently attached to the bag itself. It is this padded panel that presses against the occupant’s knees, not the airbag.

This pressure against the knees and legs, along with the firing of the seatbelt pre-tensioners, holds the occupants in their proper seated position at the moment of a frontal collision. An inflated knee airbag increases the chance of the driver and front-seat occupant remaining out of the 10-inch and 18-inch inflation zones of the frontal airbags. It also reduces the risk of “submarining” – the gliding of occupants under their seatbelts, crushing them under the dash and instrument panel on the floorboard.

The popularity of knee airbag systems among automakers is also due in part to the fact that having knee airbags allows the “show surface” of the instrument panel to be designed farther from the front seats, giving the front seat occupant more legroom.

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