GMC 1997 Safari Owner's Manual page 262

While refueling, place the cap in the holder on the fuel
filler door.
To take off the cap, turn it slowly to the left
(counterclockwise). The cap has a spring in
it; if you let
go of the cap too soon, it will spring back to the right.
/ I \
CAb I'ION:
If you get gasoline on yourself and then
something ignites it, you could be badly burned.
Gasoline can spray out on you if you open the
fuel filler cap too quickly. This spray can happen
if your tank is nearly full, and is more likely in
hot weather. Open the fuel filler cap slowly and
wait for any "hiss" noise to stop. Then unscrew
the cap all the way.
Be careful not to spill gasoline. Clean gasoline from
painted surfaces as soon as possible. See "Cleaning the
Outside of Your Vehicle" in the Index.