What Makes An Airbag Inflate; How Does An Airbag Restrain - GMC Sierra 2008 Owner's Manual

Vehicles with dual stage airbags also have seat position
sensors which enables the sensing system to monitor
the position of the driver's seat. The seat position sensor
provides information that is used to determine if the
airbags should deploy at a reduced level or at full
deployment.
Your vehicle may or may not have roof-rail airbags.
See Airbag System on page 1-67. Roof-rail airbags are
intended to inflate in moderate to severe side crashes.
In addition, these roof-rail airbags are intended to inflate
during a rollover or in a severe frontal impact. Roof-rail
airbags will inflate if the crash severity is above the
system's designed threshold level. The threshold level
can vary with specific vehicle design.
Roof-rail airbags are not intended to inflate in rear
impacts. Both roof-rail airbags will deploy when either
side of the vehicle is struck, or if the sensing system
predicts that the vehicle is about to roll over, or in
a severe frontal impact.
In any particular crash, no one can say whether an
airbag should have inflated simply because of the
damage to a vehicle or because of what the repair costs
were. For frontal airbags, inflation is determined by
what the vehicle hits, the angle of the impact, and how
quickly the vehicle slows down. For roof-rail airbags,
deployment is determined by the location and severity of
the side impact. In a rollover event, roof-rail airbag
deployment is determined by the direction of the roll.
What Makes an Airbag Inflate?
In a deployment event, the sensing system sends an
electrical signal triggering a release of gas from the
inflator. Gas from the inflator fills the airbag causing the
bag to break out of the cover and deploy. The inflator,
the airbag, and related hardware are all part of the
airbag module.
Frontal airbag modules are located inside the steering
wheel and instrument panel. For vehicles with roof-rail
airbags, there are airbag modules in the ceiling of the
vehicle, near the side windows that have occupant
seating positions.

How Does an Airbag 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.
Airbags supplement the protection provided by safety
belts. Frontal airbags distribute the force of the
impact more evenly over the occupant's upper body,
stopping the occupant more gradually. Roof-rail airbags
distribute the force of the impact more evenly over
the occupant's upper body.
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