Why do air bags sometimes fail to deploy during a crash?

NATIONAL – The activation of an air bag in a crash is dependent on several important factors including: the characteristics of the crash (e.g., speed, other vehicle(s) involved, impact direction, etc.); the individual vehicle air bag system’s design strategy; and the crash sensor locations. Air bags are not intended to deploy in all crashes. There may be circumstances when an air bag does not deploy. Some possible examples follow:
The crash conditions may be sufficiently moderate where an air bag would not be needed to protect an occupant wearing a seat belt. The seat belt may provide sufficient protection from a head or chest injury in such a crash.
Many advanced frontal air bag systems automatically turn off the passenger air bag when the vehicle detects a small-stature passenger or child, child in a child restraint system, or no occupant in the right front passenger seat.
Some advanced side air bag systems will similarly shut off the passenger side air bag system when detecting a small-stature passenger or child in the right front passenger seat who is positioned too close to the side air bag.
Some vehicles, such as pick-up trucks or sports cars without rear seats, may have a manual ON-OFF switch for the front passenger air bag. If the manual ON-OFF switch is positioned in the “off” position, the front passenger air bag will not deploy.
An air bag may also not deploy or work properly if the vehicle’s air bag readiness light is illuminated. When illuminated, the air bag readiness light warns consumers of potential problems with a vehicle’s air bag system. (If an air bag readiness light is illuminated, the vehicle should be serviced without delay.)
In used vehicles, a possible reason for the air bag not to deploy is that the air bag may not have been replaced after a previous crash. NHTSA recommends that 1) Air bags always be replaced after a deployment and 2) If, for any reason, a deployed air bag is not replaced, this information about the non-functioning air bag should be disclosed to the new owner upon the sale of the vehicle.
Any air bag that fails to deploy in an injury-producing crash should be reported to NHTSA’s Office of Defects Investigation for investigation of possible system defects and potential recall. You can file a report by phone at 888-327-4236, or by mail at the following address: National Highway Traffic Safety Administration, Office of Defects Investigation, 1200 New Jersey Avenue, SE, Washington, DC, 20590.

SOURCE: http://www.safercar.gov/

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