airbag

An airbag is a fabric envelope, typically made from nylon, that inflates rapidly during a collision to cushion occupants against impact with the vehicle interior. The system consists of three core components: a sensor that detects sudden deceleration, an inflator unit containing a chemical propellant, and the bag itself. When triggered, the inflator ignites sodium azide or other energetic compounds, generating nitrogen gas that fills the bag in roughly 30 to 50 milliseconds, well before an unrestrained occupant would strike the dashboard, steering wheel, or side panel.

Modern vehicles deploy multiple airbags in different positions. The traditional frontal airbag, mounted in the steering wheel hub or dashboard, protects drivers and front passengers from head and chest trauma. Side-impact airbags, housed in seat frames or door panels, cushion the torso during lateral collisions. Curtain airbags run along the roof line to protect the head in side impacts and rollovers. Some vehicles also install airbags behind rear seats and in the seat bolsters themselves. Each type uses a separate sensor circuit so that deployment can be tailored to the direction and severity of the crash.

Deployment and failure modes

Airbag sensors measure deceleration rates, typically triggering deployment only when impact exceeds a threshold of roughly 13 to 15 g-forces, enough to reflect a genuine crash rather than a pothole or curb strike. A diagnostic circuit continuously monitors the system, checking electrical continuity and sensor function. Failures can occur if sensors corrode, wiring connections loosen, or the inflator charge degrades over time. Premature deployment, usually caused by electrical faults, is rare but dangerous; late or non-deployment from sensor failure or chemical deterioration leaves occupants unprotected.

The airbag itself must rupture or vent once it has absorbed the impact, allowing gas to escape so that it does not suffocate the occupant or prevent them from moving. The bag fabric is engineered to tear along predetermined seams or through ports sized to bleed off pressure within a few hundred milliseconds. Improper venting can trap the occupant against the bag; excessive venting allows the bag to deflate too quickly and lose protective effect.

Airbags work most effectively in conjunction with seatbelts, which restrain the torso and reduce forward motion so the bag has less distance to decelerate the head and chest. Occupants sitting too close to the steering wheel or dashboard face risk of injury from the bag itself, since the inflator reaches temperatures exceeding 200 degrees Celsius and the bag expands with significant force. Children and small-stature adults are at higher risk, which is why many regions now mandate that front passenger airbags can be disabled manually if needed.