How does an air bag work

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 itself, which is made of 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 miles per hour (16 to 24 kph).

Finally, there is the inflation system. Air bags are actually inflated by the equivalent 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 or dashboard as it expands. About a second later, the bag is already deflating (it has holes in it) in order to get out of your way.

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