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