How does an airbag work?

★ wanayoo — archive 1999 http://howstuffworks.com/question130.htm

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Question

How does an airbag work? Do they use compressed air or what? Thanks for a great site!

Answer

Air bags have saved thousands of lives since their introduction in the early 1980s. If you run into something, your air bag can inflate in less than a tenth of a second to protect you from the forces of a head-on collision.

There are three parts to an air bag. First there is the bag iself, which is made of a thin nylon fabric and folded into the steering wheel or the dash board. Then there is the sensor that tells the bag to inflate. It detects a collision force equal to running into a brick wall at 10 to 15 MPH.

Finally there is the inflation system. Air bags are actually inflated by the equivilent of a solid rocket booster. Sodium azide (NaN₃) and potassium nitrate (KNO₃) react very quickly to produce a large pulse of hot nitrogen gas. This gas inflates the bag, which literally bursts out of the steering wheel as the bag expands. About a second later the bag is already deflating (it has holes in it) to get out of your way.

Here's some interesting links to learn more:

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