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An airbag is a vehicle occupant-restraint system using a bag designed to inflate in milliseconds during a collision and then deflate afterwards. It consists of an airbag cushion, a flexible fabric bag, an inflation module, and an impact sensor. The purpose of the airbag is to provide a vehicle occupant with soft cushioning and restraint during a collision. It can reduce injuries between the flailing occupant and the vehicle's interior.

The airbag provides an energy-absorbing surface between the vehicle's occupants and a steering wheel, instrument panel, body pillar, headliner, and windshield. Modern vehicles may contain up to ten airbag modules in various configurations, including driver, passenger, side-curtain, seat-mounted, door-mounted, B- and C-pillar mounted side-impact, knee bolster, inflatable seat belt, and pedestrian airbag modules.

During a crash, the vehicle's crash sensors provide crucial information to the airbag electronic controller unit (ECU), including collision type, angle, and severity of impact. Using this information, the airbag ECU's crash algorithm determines if the crash event meets the criteria for deployment and triggers various firing circuits to deploy one or more airbag modules within the vehicle. Airbag module deployments are activated through a pyrotechnic process designed to be used once as a supplemental restraint system for the vehicle's seat belt systems. Newer side-impact airbag modules consist of compressed-air cylinders that are triggered in the event of a side-on vehicle impact.

The first commercial designs were introduced in passenger automobiles during the 1970s, with limited success and caused some fatalities. Broad commercial adoption of airbags occurred in many markets during the late 1980s and early 1990s.

Full article: Airbag