GMC Sierra 2005 Owner's Manual page 70

Here are the most important things to know about the
airbag system:
CAUTION:
{
You can be severely injured or killed in a crash
if you are not wearing your safety belt — even
if you have airbags. Wearing your safety belt
during a crash helps reduce your chance of
hitting things inside the vehicle or being
ejected from it. Airbags are designed to work
with safety belts, but do not replace them.
Airbags are designed to deploy only in
moderate to severe frontal and near frontal
crashes. They are not designed to inflate in
rollover, rear or low-speed frontal crashes,
or in many side crashes. And, for some
unrestrained occupants, airbags may provide
less protection in frontal crashes than more
forceful airbags have provided in the past.
Everyone in your vehicle should wear a safety
belt properly — whether or not there is an
airbag for that person.
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CAUTION:
{
Airbags inflate with great force, faster than
the blink of an eye. If you are too close to an
inflating airbag, as you would be if you were
leaning forward, it could seriously injure you.
Safety belts help keep you in position before
and during a crash. Always wear your safety
belt, even with airbags. The driver should sit
as far back as possible while still maintaining
control of the vehicle.