Glossary: Airbag (SRS)

An airbag, a.k.a. a Supplementary Restraint System (SRS), is a flexible membrane or envelope that prevents impact of the driver’s chest and face colliding with the steering wheel in the event of a collision. An airbag might also be installed in various other parts of the cabin to protect the passengers from severe injuries. Analysis of accidents has concluded that, in 68% of cases, an airbag provides a significant safety measure.

The system uses a number of deceleration sensors installed at the front of the vehicle to sense the beginning of a frontal impact. When there is a moderate to severe frontal crash that requires the air bag to deploy, a signal is sent to the inflator unit. An igniter begins a rapid chemical reaction generating nitrogen gas (N2) to fill the air bag making it deploy through the module cover. Airbags inflate and deflate in about 0,05 seconds. The speed of the airbag coming out of the steering wheel hub or dashboard is roughly about 220 mph.

The entire system consists of the following parts:

- A thin bag made of nylon fabric, which is folded into the steering wheel or dashboard or anywhere else in the car.

- A sensor, which instructs the bag to inflate. The sensors receive information from an accelerometer built into a microchip and thus in the event of rapid deceleration(event of collision), it informs the airbag to inflate.

- The airbag’s inflator unit. Sodium azide (NaN3) and Potassium nitrate (KNO3) react in here produce nitrogen gas. This Nitrogen gas inflates the airbag.