How do air bags protect us in collisions?

Answer 1

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 the doors, for deploying the side airbags. The front and the side sensors only work with the front and the 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 inflater, 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 (nitrogen actually constitutes 78% of the air that we inhale). One just needs to open the doors or windows for the gas and the powder to escape.

The side airbag system differs from the one in the front. It uses a stored-gas inflater 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.