Chevrolet 2004 Impala Owner's Manual page 270

While refueling, let the fuel cap hang by the tether
below the fuel fill opening.
To remove the fuel cap, turn it slowly to the left
(counterclockwise).
5-8
CAUTION:
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If you spill fuel and then something ignites it,
you could be badly burned. Fuel can spray out
on you if you open the fuel cap too quickly.
This spray can happen if your tank is nearly
full, and is more likely in hot weather. Open
the fuel cap slowly and wait for any "hiss"
noise to stop. Then unscrew the cap all
the way.
Be careful not to spill fuel. Don't top off or overfill your
tank, and wait a few seconds after you've finished
pumping before you remove the nozzle. Clean fuel from
painted surfaces as soon as possible. See Cleaning
the Outside of Your Vehicle on page 5-90. When filling
the tank do not overfill by squeezing in much more
fuel after the pump shuts off.