How Does an Airbag Work? Simply Explained
How does an airbag work?
An airbag is a gas-filled air cushion that deploys within 30 milliseconds during a collision and cushions the impact for occupants. Crash sensors detect the impact, the control unit evaluates the data and ignites the gas generator – a controlled chemical reaction fills the air cushion in fractions of a second.
The airbag, together with the seat belt, is part of the vehicle's passive safety system. Both systems are coordinated with each other: the belt keeps the occupant in position, while the airbag cushions the impact on the steering wheel, dashboard or side structure. Without a fastened seat belt, the airbag cannot provide optimal protection.
Airbag structure
An airbag system consists of four main components: the air cushion (nylon fabric), the gas generator (produces the filling gas), the control unit (electronics center) and the crash sensors (detect the impact). All parts work in perfect harmony.
| Component | Function | Position in vehicle |
|---|---|---|
| Air cushion | Catches the occupant on impact | Steering wheel, dashboard, side trim, roof frame |
| Gas generator | Produces nitrogen to fill the air cushion | Installed behind the air cushion in the module |
| Airbag control unit | Evaluates sensor data, triggers airbag | Under the center console (central) |
| Crash sensors | Measure deceleration/acceleration on impact | Front, sides, partially rear |
| Spiral spring | Electrical connection to steering wheel airbag | Between steering column and steering wheel |
| Belt tensioner | Tightens the belt instantly on impact | In the belt buckle or belt retractor |
Step by step: How the airbag deploys
Airbag deployment takes only about 30-50 milliseconds – from impact to fully deployed air cushion. The control unit decides in less than 10 milliseconds, based on sensor data, whether and which airbags need to be triggered.
- Impact (0 ms):The vehicle hits an obstacle, crash sensors measure strong deceleration
- Signal processing (5-10 ms):The control unit compares sensor data with stored crash patterns and determines accident severity
- Deployment decision (10 ms):If the crash is severe enough, the control unit sends the ignition current to the gas generator
- Ignition (10-15 ms):The ignition pellet ignites the propellant charge (sodium azide), gas is created through chemical reaction
- Deployment (15-30 ms):Nitrogen flows into the air cushion, the cover cap breaks at predetermined breaking points
- Full deployment (30 ms):The airbag is fully inflated and catches the occupant
- Deflation (50-100 ms):The air cushion releases gas in a controlled manner and collapses
Why does the airbag deflate so quickly?
After about 100 milliseconds, the air cushion has already collapsed. There are two reasons for this: First, the occupant should not be trapped between the airbag and the seat. Second, rescue personnel must have unobstructed access to occupants after the accident.
The gas generator: The heart of the system
The gas generator contains a propellant charge made of sodium azide tablets and an electrical ignition pellet. When triggered, an electrical impulse heats a thin wire in the ignition pellet, which ignites the propellant charge. The resulting gas (nitrogen) is filtered and cooled before being directed into the air cushion.
| Gas generator type | How it works | Application |
|---|---|---|
| Pyrotechnic | Solid propellant charge (sodium azide) is ignited | Classic, widely used |
| Hybrid | Compressed gas + small propellant charge as trigger | Modern, more uniform filling |
| Cold gas | Compressed gas only, mechanical triggering | Rare, e.g. knee airbags |
What types of airbags are there?
Modern vehicles have up to 12 different airbags: driver and passenger front airbags, side airbags, head/curtain airbags, knee airbags and sometimes also rear and center airbags. Each airbag is optimized for its position and the body area it protects.
| Airbag type | Position | Protection area |
|---|---|---|
| Driver airbag | In steering wheel | Head and upper body of driver |
| Passenger airbag | In dashboard | Head and upper body of passenger |
| Side airbag | In seat backrest or door trim | Chest and pelvis |
| Head/curtain airbag | In roof frame | Head in side impact |
| Knee airbag | Under dashboard | Knees and lower legs |
| Center airbag | Between front seats | Prevents occupants from colliding |
What happens after deployment?
After an airbag is deployed, all triggered airbags, belt tensioners and in many cases the control unit must be replaced or repaired. The control unit stores crash data and locks itself – this data must be professionally deleted before further use.
- Deployed airbags:Must be completely replaced (no reset possible)
- Belt tensioners:Also one-time use – must be replaced
- Control unit:Stores crash data in EEPROM, must be repaired
- Crash sensors:Often damaged in the impact area, must be checked
- Trim panels:Cover caps on steering wheel/dashboard are broken
Delete crash data at Airbag24
After an accident with airbag deployment, the control unit stores crash data and must be repaired. Airbag24 professionally deletes the crash data and resets the control unit – for all makes and models, TÜV-certified and with over 20 years of experience.
- Delete crash data:Control unit is reset from locked state
- All makes:VW, Audi, BMW, Mercedes, Opel, Ford, Seat, Skoda and many more
- Spare parts:Crash sensors, spiral springs and belt tensioners in shop
- Repair time:3-4 business days (express on request)
- Cost savings:Up to 50% cheaper than a new control unit
Frequently asked questions about airbag function
Here you will find answers to the most important questions about how airbags work.
Does the airbag deploy in every accident?
No, the airbag only deploys if the accident is severe enough. The control unit compares sensor data with stored crash patterns and decides individually. In minor rear-end collisions or parking lot bumps, no airbag deploys – the deceleration forces are too low.
Can an airbag deploy without an accident?
With an intact system, accidental deployment is extremely unlikely. Only with faulty gas generators (as in the Takata recall) or with massive electronic defects can unintended deployment theoretically occur. This is why regular inspections and participation in recall campaigns are important.
Does the airbag work with the ignition off?
No, with the ignition off, the airbag system is not active. However, the control unit has an energy reserve (capacitors) that can still trigger the airbag if the battery is damaged during impact – but only with the ignition on.
How dangerous is a deployed airbag?
An airbag deploys at high speed and force. With correct seating distance (at least 25 cm from the steering wheel), the airbag provides reliable protection. However, insufficient distance, incorrect seating position or unfastened seat belts can lead to injuries from the airbag itself.