Even the best belt designs can't prevent all head and chest impacts in serious frontal crashes. Air bags help by creating an energy-absorbing cushion between the upper body and steering wheel, instrument panel, or windshield. To get the maximum benefits, you should use a belt and sit away from the bag. This way, you'll be in position with sufficient space for the air bag to inflate rapidly and create a protective buffer.
Driver deaths in frontal crashes are about 20 percent lower with air bags than in similar cars without them. At the time of publication, it has been estimated that more than 2,500 lives have been saved. But in some circumstances, air bags can cause injuries, mostly minor, but occasionally serious or, in rare cases, fatal. The most serious injuries occur when people are very close to air bags when they first begin to inflate. Some of the deaths have been infants in rear-facing restraints and unrestrained or improperly restrained children. This risk can be eliminated by making sure all youngsters travel in the back seat.
Although different manufacturers' systems vary slightly, the air bag system is composed of a few basic parts. Two sensors located in the area of the front bumper, or in the firewall area, sense the impact. The sensors activate inflator(s) that blow-up a passenger air bag in the right-hand side of the dashboard, and a driver air bag located in the steering wheel hub.
The system has an indicator lamp activated by the ignition key to let you know the system is working. If the car is involved in a frontal crash equivalent to running into a stationary barrier at least 10-12 mph, the sudden deceleration (impact) causes the sensor to activate a gas cartridge that instantly inflates the air bag preventing the occupants from contacting the inside of the vehicle. The air cushions absorb the impact.
The air bags themselves are porous and the air is actually beginning to escape as they are being inflated. The entire process (sensing, inflation and partial deflation) is completed in about 1⁄25 th of a second, or about the time it takes to blink your eye.