GMC 2002 Envoy Owner's Manual page 39

What makes an air bag inflate?
In an impact of sufficient severity, the air bag sensing
system detects that the vehicle is in a crash. For both
frontal and side impact air bags, the sensing system
triggers a release of gas from the inflator, which inflates
the air bag. The inflator, air bag and related hardware
are all part of the air bag modules inside the steering
wheel, instrument panel and the side of the front
seatbacks closest to the door.
How does an air bag restrain?
In moderate to severe frontal or near frontal collisions,
even belted occupants can contact the steering wheel or
the instrument panel. In moderate to severe side
collisions, even belted occupants can contact the inside
of the vehicle. The air bag supplements the protection
provided by safety belts. Air bags distribute the force of
the impact more evenly over the occupant's upper body,
stopping the occupant more gradually. But the frontal air
bags would not help you in many types of collisions,
including rollovers, rear impacts, and side impacts,
primarily because an occupant's motion is not toward
the air bag. Side impact air bags would not help you in
many types of collisions, including frontal or near
frontal collisions, rollovers, and rear impacts, primarily
because an occupant's motion is not toward those air
bags. Air bags should never be regarded as anything
more than a supplement to safety belts, and then only in
moderate to severe frontal or near
the driver's and right front passenger's frontal air bags,
and only in moderate to severe side collisions for the
driver's and right front passenger's side impact air bags.
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frontal collisions for
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