GMC 2010 Sierra Denali Owner's Manual page 98

Vehicles with dual stage airbags also have a driver's
seat position sensor which enables the sensing system
to monitor the position of the driver seat (all models).
The seat position sensor provides information that is
used to determine if the airbags should deploy at a
reduced level or at full deployment.
The vehicle may or may not have seat mounted side
impact and roof-rail airbags. See Airbag System on
page 2 56. Seat mounted side impact and 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. Seat mounted side impact and 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.
2-62
Roof-rail airbags are not intended to inflate in rear
impacts. A seat mounted side impact airbag is intended
to deploy on the side of the vehicle that is struck. 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 seat mounted side
impact and 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.