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How do Airbags Work?

Stephen Rampur
Airbags are an ingenious invention. They protect people traveling in a vehicle, in case of an accident. Do you know what makes them pop out to save your head in an accident? The answers are forthcoming in this story.

Did You Know?

Airbags are known by many technical names, such as Supplementary Restraint System (SRS), Air Cushion Restraint System (ACRS), and Supplemental Inflatable Restraint (SIR).
Airbags are one of the safety features that can be incorporated in your car to protect you in the event of an accident. The use of an airbag can protect your head, neck, and chest areas. They are fixed by the vehicle manufacturers for the safety of the driver and passengers.
Normally, they emerge out of the steering wheel or from the dashboard, within a few milliseconds of the collision. When your head hits the airbag, the bag starts deflating slowly, allowing you to get out of the car. In some cars, when the speed exceeds 200-300 mph, airbags deploy automatically, even in the absence of a collision.
Often airbags may prove inadequate, if you aren't wearing a seat-belt. Due to the increasing number of accidents, governments of many countries have made the use of seat-belts mandatory, which is said to have effectively reduced the number of injuries, due to vehicle accidents. However, the latest designs in airbags can protect the person.
There is a common misconception that airbags stop our body from being thrown forward after a collision. They are actually meant for protecting the driver's head, and stop it from hitting the steering wheel. It is the seat-belt that keeps the driver in his seat, even after a collision.
If the seat-belt and airbag work together, they can completely eliminate the possibility of an injury, even in severe car crashes.

Working of an Airbag

When the crash sensor in the car detects a collision, it sends a signal to the control module which deploys the airbag. There are various types of crash sensors, like the older ones which were placed in the front of the car (in the crash zone area), and the latest micromachined accelerometers that are installed inside the control module or the airbag brain.
The micromachined accelerometers actually measure the speed and severity of the collision. There are also sensors placed in doors, for deploying side airbags. The front and the side sensors only work with the front and side airbags, respectively.
An airbag installed in the dashboard or in the steering wheel will only be deployed, if there is a front-end collision, such as in the case of a head-on collision or within 30 degrees from any side from the core of the car. The same rule applies to airbags installed at the sides of the car.
The airbag is deployed when the car is hit at a certain angle. The ones on the left won't deploy, if the collision is on the right side and vice versa.
The control module, or the airbag brain, is a small computer that receives data of the crash from different sensors, and then decides which airbag is to be deployed. It is unable to deploy an airbag, if it receives only one pulse. It would need two or more pulses from the sensors to do so.
The second pulse comes from the arming sensor that is located inside the car, which senses a sudden decrease in speed. When the control module is certain about a severe crash, it signals the squib inflator, also known as the igniter, which is an electrical device that has a thin bridge wire.
As the current flows through the wire, it overheats, and ignites the airbag propellant which is made of sodium azide. Sodium azide is a fast-burning fuel that produces large amounts of nitrogen gas, which goes through filters and fills the nylon airbags.
After your head hits the nitrogen-filled bag, the bag deflates by releasing the gas through tiny holes. The cloud of smoke that fills the vehicle, is actually talcum powder or cornstarch. The powder prevents the bag from sticking to itself, while it's folded inside.
The nitrogen gas that is released from the tiny holes is absolutely harmless. One just needs to open the doors or windows, for the gas and powder to escape.
The side airbag system differs from the one in the front. It uses a stored-gas inflator which consists of a cylinder that incorporates 3000-4000 psi of compressed argon gas. The control module signals the igniter, which melts a tiny bladder inside the cylinder. The argon gas then fills the airbag and helps inflate it.
Like nitrogen, argon is also harmless. If you are planning on buying a car, ensure that it has an airbag system. With the use of seat-belts and airbags, injuries caused in vehicle crashes have reduced considerably throughout the world.