There isn't a readily accessible, easily located fuel pump cut-off switch on a 1999 Chevrolet Prism (or most other passenger vehicles of that era for that matter). Unlike some heavier equipment or older vehicles, fuel pump shutoff is typically handled through the car's electrical system and controlled by the computer. Disconnecting the battery's negative terminal is the most common and effective way to cut off power to the fuel pump in an emergency.
If you need a dedicated shut-off switch, it would have to be professionally installed.
