How airbags work？

An airbag is actually one component of a three 3part system that protects the occupants of a vehicle in the event of a crash. The system consists of airbag module,  crash sensor, and diagnostic unit. Newer vehicles may also have an on/off switch that allows the system to be turned off.

The airbag module (is the actual "airbag") is a bag made of lightweight fabric and is located on the steering wheel pad or center console of the dashboard along with the inflator module. It consists of the inflator unit and the lightweight fabric airbag. The driver's airbag is much smaller than the passenger's airbag due to the distance between the airbag and the occupant and the physical space the airbag is housed in.

The crash sensor is usually located on the vehicle's bumper or grille, but may be located in the dashboard or passenger compartment in some models. There may be only one sensor or multiple sensors in a vehicle. Although it is commonly believed that the sensors are activated by impact, they are actually triggered by the rapid deceleration or rate of deceleration of the vehicle. Therefore, the sensors do not activate at the same rate in different speeds and crashes. Sudden braking, or driving over rough or uneven roads, will not usually produce enough deceleration rate to trigger the sensor to activate the system if the system is functioning properly.

The final component is the diagnostic unit, which monitors the status of the airbag system. When the vehicle ignition is on, the diagnostic unit checks for functional problems within the system and illuminates a warning light to alert the driver that the system is not functioning properly. To protect against power failure, most diagnostic units store enough power to trigger the airbag if the vehicle battery is damaged in a collision.

When the vehicle decelerates sufficiently, the airbag is designed to perform two main functions. The airbag is designed to provide a soft "cushion" between the occupant and the hard surfaces inside the vehicle and to spread the energy of the collision over a wider area. The deceleration sensor triggers the inflation of the airbag during rapid deceleration and deflates it within a few seconds. A front-end collision with a solid, stationary object, such as a tree, at speeds of 10 to 15 miles per hour (equivalent to a 28 mph front-end collision with another vehicle, as the other vehicle absorbs some of the energy) triggers inflation, activating a mechanical switch that closes electrical contacts, signaling the sensor that a collision has occurred. The airbag's inflation system contains sodium&azide (NaN3) and potassium nitrate (KNO3), which combine to produce nitrogen gas. The nitrogen mixture inflates the airbag at speeds approaching 200 miles per hour.

When an airbag is functioning properly, it can reduce the frequency and severity of injuries in a vehicle accident. The effectiveness of a properly functioning airbag is enhanced by wearing a lap/shoulder restraint, such as a seat belt, and a structurally sound vehicle roof.