There isn't a single, universally located "emergency fuel shutoff switch" on a 1993 Pontiac Transport (or most passenger vehicles of that era). Modern cars often have fuel pump inertia switches, which shut off the fuel pump in a collision to prevent fires. However, these are typically located under the vehicle, often near the fuel tank, and are not intended as an easily accessible emergency shut-off.
To stop the fuel flow in an emergency situation with a 1993 Pontiac Transport, your best bet would be to disconnect the negative (-) cable from the battery. This will cut power to the entire vehicle, including the fuel pump. Remember that this also disables all other electrical systems. This should only be done if there is an immediate and serious fire risk.
