| The air bag system consists of three basic | | | | government-specified criteria and who receive |
| parts-an air bag module, crash sensors and a | | | | government permission. |
| diagnostic unit. Some systems may also have an | | | | Initially, most vehicles featured a single airbag, |
| on/off switch, which allows the air bag to be | | | | mounted in the steering wheel and protecting the |
| deactivated. | | | | driver of the car (who is the most at risk of |
| The air bag module contains both an inflator unit | | | | injury). During the 1990s, airbags for front seat |
| and the lightweight fabric air bag. The driver air | | | | passengers, then separate side impact airbags |
| bag module is located in the steering wheel hub, | | | | placed between the door and occupants, became |
| and the passenger air bag module is located in the | | | | common. |
| instrument panel. When fully inflated, the driver air | | | | Many advanced air bag technologies are being |
| bag is approximately the diameter of a large | | | | developed to tailor air bag deployment to the |
| beach ball. The passenger air bag can be two to | | | | severity of the crash, the size and posture of the |
| three times larger since the distance between the | | | | vehicle occupant, belt usage and how close that |
| right-front passenger and the instrument panel is | | | | person is to the air bag module. Many of these |
| much greater than the distance between the | | | | systems will use multi-stage inflators that deploy |
| driver and the steering wheel. | | | | less forcefully in stages in moderate crashes than |
| The crash sensors are located either in the front | | | | in very severe crashes. Occupant sensing devices |
| of the vehicle and/or in the passenger | | | | let the air bag diagnostic unit know if someone is |
| compartment. Vehicles can have one or more | | | | occupying a seat in front of an air bag, whether |
| crash sensors. The sensors are typically activated | | | | the person is an adult or a child, whether a seat |
| by forces generated in significant frontal or | | | | belt or child restraint is being used and whether |
| near-frontal crashes. Sensors measure | | | | the person is forward in the seat and close to the |
| deceleration, which is the rate at which the vehicle | | | | air bag module. Based on this information and |
| slows down. Because of this, the vehicle speed at | | | | crash severity information, the air bag is deployed |
| which the sensors activate the air bag varies with | | | | at either a high force level, a less forceful level or |
| the nature of the crash. Air bags are not designed | | | | not at all. |
| to activate during sudden braking or while driving | | | | Many new vehicles are also equipped with side air |
| on rough or uneven surfaces. In fact, the | | | | bags. While there are several types of side air |
| maximum deceleration generated in the severest | | | | bags, all are designed to reduce the risk of injury |
| braking is only a small fraction of that necessary | | | | in moderate to severe side impact crashes. These |
| to activate the air bag system. | | | | air bags are generally located in the outboard |
| The diagnostic unit monitors the readiness of the | | | | edge of the seat back, in the door or in the roof |
| air bag system. The unit is activated when the | | | | rail above the door. |
| vehicle's ignition is turned on. If the unit identifies a | | | | The Citroën C4 provides the first "shaped" |
| problem, a warning light alerts the driver to take | | | | driver airbag - made possible by this car's |
| the vehicle for examination of the air bag system. | | | | innovative fixed hub steering wheel. |
| Most diagnostic units contain a device that stores | | | | Seat and door-mounted air bags all provide upper |
| enough electrical energy to deploy the air bag if | | | | body protection. Some also extend upwards to |
| the vehicle's battery is destroyed very early in a | | | | provide head protection. Two types of side air |
| crash sequence. | | | | bags, known as inflatable tubular structures and |
| Some vehicles without rear seats, such as pick-up | | | | inflatable curtains, are specifically designed to |
| trucks and convertibles, or with rear seats too | | | | reduce the risk of head injury and/or help keep |
| small to accommodate rear-facing child safety | | | | the head and upper body inside the vehicle. A few |
| seats, have manual ON/OFF switches for the | | | | vehicles are now being equipped with a different |
| passenger air bag installed at the factory. ON/OFF | | | | type of inflatable curtain designed to help reduce |
| switches for driver or passenger air bags may | | | | injury and ejection from the vehicle in rollover |
| also be installed by qualified service personnel at | | | | crashes. |
| the request of owners who meet | | | | |