How are airbags deployed?

Airbag 1 deployment

The airbag (airbag) is a component of passive safety in automobiles. Like the seat belt, the airbag is one of the occupant restraint systems in motor vehicles.

Abbreviation: SRS = Safety Restraint System or Supplement Restraint System

Brief history of the airbag

  • Mercedes received the patent for the airbag in 1971

  • In 1980, an airbag system was offered as an extra for luxury vehicles for the first time

  • In 1987 the first Volvo with a driver airbag came onto the market in the USA, the Volvo 760.

  • The installation of an airbag has been mandatory in America since 1990


Airbag deployment (Source: Mercedes)

Triggering and process of the airbag ignition

With modern airbag systems, it is triggered as soon as
a frontal impact at speeds greater than 30 km / h or
there is a frontal impact at speeds greater than 30 km / h and a lateral offset of up to 30 °.

After an accident, drivers often wonder why the airbag did not deploy. The triggering algorithms that ultimately lead to the triggering command coming are quite complicated. Not every impact triggers a trip.

A distinction is made between different crash severities and trigger thresholds.

Crash severity

Through numerous crash and driving tests under extreme conditions, the triggering thresholds were set by BMW for all possible types of accidents. The trigger thresholds depend on the severity of the crash. The crash severity is divided into 4 groups:


- CS 0: no pyrotechnic restraint systems necessary
- CS 1: slight crash
- CS 2: moderate crash
- CS 3: severe crash

Trip levels

The trigger levels were set depending on theCrash severity as well as taking into account other factors such as direction, Overlay on impact and depending on the evaluation, whether the inmate is belted or not. This results in different trigger thresholds for activating the various restraint systems. Due to the different triggering thresholds, the triggering for the second stage of the front airbags can be varied depending on the severity of the crash.

Using the following exampleFront crash (Source BMW) the possible activated actuators are shown:

In the case of a front crash, a distinction is made between crash severity "light to moderate collision" (CS 1 / CS 2) and "severe collision" (CS 3).

Crash severity CS1

In the event of a severity of crash CS1 (minor collision), the belt tensioners are triggered. The driver / front passenger airbag is not deployed if it is detected that the occupants are wearing seat belts. Exception: if the occupants are not wearing their seat belts, the driver and front passenger airbags are triggered.

Crash severity CS2

From crash severity CS 2 (moderate collision), the driver / front passenger airbag and the belt tensioner are triggered. The safety battery terminal is activated, the electric fuel pump is switched off and an emergency call is made if a suitably prepared telephone is available in the vehicle.

Crash severity CS3

In the case of a crash severity CS3 (severe collision), the driver / front passenger airbag and the belt tensioner are triggered, but with a different time delay.

Trigger example front crash (BMW E60)

(Source BMW)

Short video on airbag deployment

Another funny video about airbag deployment.

Is the video a fake video? Can the airbag even deploy when the vehicle is stationary?