Buick Century 2003 Owner's Manual page 64

When Should an Air Bag Inflate?
The driver's and right front passenger's frontal air bags
are designed to inflate in moderate to severe frontal
or near-frontal crashes. But they are designed to inflate
only if the impact speed is above the system's
designed "threshold level."
If the front of your vehicle goes straight into a wall that
does not move or deform, the threshold level is
about 12 to 18 mph (19 to 29 km/h). The threshold level
can vary, however, with specific vehicle design, so
that it can be somewhat above or below this range.
If your vehicle strikes something that will move or
deform, such as a parked car, the threshold level will be
higher. The driver's and right front passenger's frontal
air bags are not designed to inflate in rollovers, rear
impacts, or in many side impacts because inflation
would not help the occupant.
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Your vehicle may or may not have a side impact air
bag. See Air Bag Systems on page 1-53 . A driver 's side
impact air bag is designed to inflate in moderate to
severe side crashes involving the driver's door. A side
impact air bag will inflate if the crash severity is
above the system's designed "threshold level." The
threshold level can vary with specific vehicle design.
A driver's side impact air bag is not designed to inflate
in frontal or near-frontal impacts, rollovers or rear
impacts, because inflation would not help the occupant.
In any particular crash, no one can say whether an
air bag should have inflated simply because of
the damage to a vehicle or because of what the repair
costs were. For frontal air bags, inflation is determined
by the angle of the impact and how quickly the
vehicle slows down in frontal and near-frontal impacts.
For side impact air bags, inflation is determined by
the location and severity of the impact.