How Airbags Work

The trusty seat belt provided the singular form of passive restraint in our cars for years.  There were discussions about their safety, especially relating to children, but finally much of the country adopted mandatory seat-belt laws. Statistics have shown that the use of seat belts has saved thousands of lives that could have been lost in collisions.  The concept of the airbag — a soft pillow to land against in a crash — has been around for years with the first commercial airbags appearing in automobiles in the 1980’s.

Since the model year 1998, all new cars sold in the United States have been mandated to have airbags on both driver and passenger sides of the vehicle. (Light trucks came under the rule in 1999.) To date, statistics show that airbags minimise the risk of dying in a direct frontal crash by about 30 percent. Later came seat-mounted and door-mounted side airbags. Today, there are cars go far beyond having dual airbags to having six or even eight airbags. Having awakened some of the same controversy that surrounded seat-belt use in its early years, airbags are the subject of earnest government and industry research and testing.

When a car crashes, the physical energy required to stop an object is very great because the car’s momentum has changed instantly while the passengers’ has not — there is not a lot of time to work with. The design of any supplemental restraint system is to help stop the passenger while doing as little damage to him or her as possible. What an airbag wants to accomplish is to slow the passenger’s speed to zero with little or no damage. The airbag has the space between the passenger and the steering wheel or dashboard and a fraction of a second in which to obtain its purpose.  Even that tiny amount of area and time is valuable, however, if the system can slow the passenger smoothly rather than forcing an abrupt stop to his or her motion. The bag itself is made of a thin, nylon fabric, which is gathered into the steering wheel or dashboard or, more recently, the seat or door.  The sensor is the tool that tells the bag to inflate.

Inflation happens when there is a crash 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 triggered when there is a mass shift that closes an electrical contact, telling the sensors that a crash has happened. The sensors receive information from an accelerometer built into a microchip. The air bag’s inflation system combines sodium azide (NaN3) with potassium nitrate (KNO3) to produce nitrogen gas. Hot blasts of the nitrogen immediately inflate the airbag. The inflation system is much like a solid rocket booster. The airbag system ignites a solid propellant, which burns extremely quick to create a large volume of gas to inflate the bag. The bag then literally bursts from its storage site at up to 200 mph (322 kph) — faster than the blink of an eye!  A second later, the gas quickly escapes through tiny holes in the bag, thus deflating the bag so you can move. Even though the whole process happens in only one-twenty-fifth of a second, the additional time is enough to help prevent serious injury. The powdery substance that is released from the airbag, is regular, everyday cornstarch or talcum powder, which is used by the airbag manufacturers to keep the air bags flexible and lubricated while it’s in storage.