Airbag

An airbag, designated SRS for Supplemental Restraint System, is a folded fabric cushion that inflates almost instantaneously during a serious collision to soften the impact between an occupant's body and the hard interior of the car. It exists to spread the deceleration forces of a crash over a larger area and a longer time, preventing the head and chest from striking the steering wheel, dashboard, pillars or glass at full speed. The word supplemental is deliberate: the airbag is engineered to work alongside the seat belt, not in place of it.

Deployment is extraordinarily fast. Crash sensors detect the sudden deceleration of an impact and signal the airbag control unit, which, if it confirms a genuine crash, fires an igniter inside the inflator. The inflator rapidly generates gas, traditionally through the burning of a solid propellant such as sodium azide in older designs or cleaner compounds in modern ones, and in some cases by releasing stored compressed gas. This fills the nylon bag in roughly twenty to thirty milliseconds, far faster than the blink of an eye. The bag then begins to deflate through vents almost immediately, so that by the time the occupant makes contact it is already yielding, cushioning the body rather than presenting a rigid surface.

The protective effect is greatest for the head and torso, the regions most vulnerable to fatal injury in a frontal crash. By catching the occupant against a large, gas-filled surface, the airbag reduces peak forces on the skull, neck and chest and lessens the risk of contact with intruding structures. Crucially, the system relies on the belt to position the occupant correctly and to slow their forward motion so that they meet the bag at the right moment and distance; an unbelted occupant can be too close when the bag fires, turning a life-saving device into a source of injury.

Modern vehicles carry far more than the single driver's airbag of early designs. Frontal airbags protect the driver and front passenger, while side airbags in the seats or doors shield the torso and pelvis in a side impact. Curtain airbags drop from the roofline to cover the side windows and protect the head of front and rear occupants and to reduce ejection, and additional units such as knee, far-side and even central airbags between front seats address specific injury patterns. Each is tuned to particular crash types.

Airbags do have limitations and maintenance considerations. They are single-use devices that must be replaced after deployment, the system self-tests at each start, and a persistent SRS warning light indicates a fault that should be investigated, since a disabled airbag offers no protection. They are designed to deploy only in significant impacts of the relevant direction, not minor knocks. The airbag works as part of an integrated restraint system, governed by the airbag electronic control unit, paired with seat-belt pretensioners and curtain or window airbags, and complemented by the car's crumple zones, which manage the structural energy the airbags are calibrated to handle.