Smash! You drive head-on into a tree. Bang! Your air bag inflates. Whew! You live.
You hope. Air bags have developed a bad rep for crushing children and small adults with their fast and furious inflation. As a result, the National Highway Traffic Safety Administration has ordered stricter standards for occupant protection and safety. Under a new ruling, auto manufacturers are required to begin phasing in advanced air-bag technology that may include occupant-weight sensors in the seats and variable-rate inflators behind the bags by 2002.
Until then, here's a look at today's state-of-the-art explosion waiting to happen right under your nose.
Crash sensors The determination of whether or not to deploy the air bag is made by electromechanical devices or, increasingly, microelectromechanical systems. Sophisticated algorithms in the air bag's control microprocessor analyze the MEMS signal and determine within 20 milliseconds whether to complete the air-bag firing circuit.
MEMS A tiny silicon mass inside the microelectromechanical system is mounted on tethers that form a spring. As the mass moves back and forth along the axis of acceleration, its force is measured by electronics that sense small changes.
Inflator housing The pyrotechnic inflator housing is generally fabricated from lightweight aluminum or stainless steel.
Air bag Dusted with cornstarch to ease opening, a standard driver-side air bag holds about 60 liters of gas, which is released through exhaust vents facing away from the occupant less than 2 seconds after the nylon bag is deployed.
Igniter When the crash-sensing circuit is completed, an electrically triggered igniter initiates a chemical chain reaction that sets off sodium-azide fuel pellets.
Steering wheel cover Folded inside a central steering wheel cavity, the deployed air bag bursts through its cover at 100 to 200 mph, fully expanding within 50 to 70 milliseconds of impact.
Fuel pellets Sodium-azide pellets or disks break down to rapidly produce a large volume of nitrogen gas.
Diffuser A diffuser cools and filters the nitrogen gas as it's expelled from the inflator to fill the air bag.
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