How Automotive Airbags Work

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When automotive airbags inflate due to a collision, they don’t fill with air. They actually fill with a gas that is created as a result of one chemical being ignited by another. The whole process is fairly simple and happens almost instantaneously when a car is involved in a collision. In this article, Part 1 looks at the history of airbags, Part 2 describes what they’re made from, Part 3 explains how they detect a collision, and Part 4 tells how the sensors work.

Part 1 of 4: Automotive airbag history

Airbags became Federally mandated standard safety equipment in all cars on September 1, 1998, thanks to legislation that was passed in 1991. Some automobile companies, however, began installing airbags in the 1970s. Statistics prove that people are 30% less likely to be killed in a front-end collision when they are in a vehicle equipped with airbags.

Part 2 of 4: What airbags are made from

Airbags are made from nylon fabric that is quite thin and pliable. There are actually tiny little holes in the nylon fabric so that the airbags can deflate right away. The airbags are carefully folded before they are installed to allow for flawless inflation upon impact. The white powdery substance that is expelled when the airbags are deployed is actually just cornstarch or plain old talcum powder. It is used as a type of lubricant that helps the airbag remain pliable and inflate smoothly.

Part 3 of 4: How a collision is detected prior to airbag deployment

Automobile manufacturers install impact sensors in cars that sense when the car is involved in a collision. These sensors used to be installed only in the front and rear of the car. Newer cars that come equipped with side airbags also have collision sensors along the sides of the car. The collision sensors contain microchips that send a signal to the airbag sensors.
  • Note: The whole airbag inflation process takes only about 50 milliseconds. This is the sequence of events that happen in those milliseconds:
  • As the car hits something, it starts to lose speed
  • The accelerometer detects this deceleration
  • This triggers the airbag circuit
  • The chemical explosive is ignited
  • Gas is generated, expanding the airbag
  • The expanding airbag pushes the cover off the steering wheel
  • The driver makes impact with the airbag
  • The impact causes the airbag to deflate

Part 4 of 4: How the sensors trigger airbag deployment

Collision sensors send an electronic signal to sensors at the base of the airbag which triggers the detonation of canisters attached to the airbags. The canisters contain a chemical called sodium azide and a special igniter compound called potassium nitrate. Sodium azide is a very stable chemical compound, until it is exposed to heat from the ignited potassium nitrate.
When it’s ignited, the sodium azide in the airbags generates nitrogen gas. The nitrogen gas is what causes the airbags to inflate. It takes only about 130 grams of sodium azide to produce 67 liters of nitrogen gas. The airbags inflate at around 200 miles per hour.
When an accident occurs, knowing that your car is equipped with airbags should make the potential impact much safer. Make sure to wear your seatbelt at all time because airbags work best if you’re buckled in.

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