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.

Airbag Safety Concerns

Since the early days of auto airbags, experts have cautioned that airbags are to be used in tandem with seat belts. Seat belts were still completely necessary because airbags worked only in front-end collisions occurring at more than 10 mph (6 kph). Only seat belts could help in side swipes and crashes (although side-mounted airbags are becoming more common now), rear-end collisions and secondary impacts.

“Even as the technology advances, airbags still are only effective when used with a lap/shoulder seat belt.”

It didn’t take long to learn that the force of an airbag can hurt those who are too close to it. Researchers have determined that the risk zone for driver airbags is the first 2 to 3 inches (5 to 8 cm) of inflation. So, placing yourself 10 inches (25 cm) from your driver airbag gives you a clear margin of safety. Measure this distance from the center of the steering wheel to your breastbone. If you currently sit less than 10 inches away, you can adjust your driving position in the following ways:

  • Move your seat to the rear as far as possible while still reaching the pedals comfortably.
  • Slightly recline the back of your seat. Although car designs vary, most drivers can achieve the 10-inch distance even with the driver seat all the way forward by slightly reclining the back of the seat. If reclining the seat makes it hard to see the road, you can raise yourself up by using your car’s seat-raising system (not all cars have this!) or a firm, non-slippery cushion to achieve the same effect.

Point the airbag toward your chest, instead of your head and neck, by tilting your steering wheel downward (this only works if your steering wheel is adjustable).

Airbag Inflation

The goal of an airbag is to slow the passenger’s forward motion as evenly as possible in a fraction of a second. There are three parts to an airbag that help to accomplish this feat:

  • The bag itself is made of a thin, nylon fabric, which is folded into the steering wheel or dashboard or, more recently, the seat or door.
  • The sensor is the device that tells the bag to inflate. Inflation happens when there is a collision force equal to running into a brick wall at 10 to 15 miles per hour (16 to 24 km per hour). A mechanical switch is flipped when there is a mass shift that closes an electrical contact, telling the sensors that a crash has occurred. The sensors receive information from an accelerometer built into a microchip.
  • The airbag’s inflation system reacts sodium azide (NaN3) with potassium nitrate (KNO3) to produce nitrogen gas. Hot blasts of the nitrogen inflate the airbag.

Early efforts to adapt the airbag for use in cars bumped up against prohibitive prices and technical hurdles involving the storage and release of compressed gas. Researchers wondered

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