One of the most important safety features found in modern cars are air bags. Essentially airbags are occupant restraints. They consist of a soft flexible container, made of nylon or a similar material, which inflates very rapidly following a collision in order to protect occupants from impacting with internal objects such as the dashboard, windscreen or steering wheel. Modern cars generally have several air bags designed to protect the driver and front seat passengers. In addition some cars have side airbags and airbags designed to protect the legs. Progressively more cars are also being fitted with rear passenger air bags too.

Airbags are designed to be used in conjunction with seatbelts rather than as stand alone restraints. Failure to wear a seatbelt can result in serious injury even if the air bag is deployed, particularly if the impact between the car occupant and the airbag occurs before the bag is fully inflated. The rate of inflation of the airbag is explosive and they are designed to be fully inflated prior to occupant impact. Controlled deceleration of the occupant is achieved by controlled deflation of the airbag.

Note that airbags are not reusable. They are inflated using a pyrotechnic device (essentially a controlled explosion) and must they be replaced after they have been deployed. In many cars en electronic system continually monitors the condition of the airbag and a warning light is switched on if any faults are detected. If this happens then it is important that the air bag system is checked by a qualified technician at the earliest opportunity.

The operation of a car’s airbag system is controlled by an ACU or airbag control unit. This is connected to an array of sensors which are distributed around the car. These sensors are essentially accelerometers, impact sensors, pressure sensors, speed sensors, gyroscopes and brake sensors along with seat occupancy sensors. The ACU continually monitors these and when a critical status is detected the ACU triggers a pyrotechnic device that produces rapidly a large volume of gas which inflates the appropriate airbags.

If a child seat is fitted in the passenger seat any corresponding airbags must be disabled in order to protect the child from a potentially lethal airbag impact.

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