Fuel delivery is controlled by the engine's computer (Powertrain Control Module or PCM) and various sensors. If there's a problem, the PCM might cut fuel flow, but this isn't a manually activated safety switch. To stop fuel flow in an emergency, you'd need to disconnect the fuel pump's electrical connector (this requires knowledge and some mechanical skills). However, this is not a recommended method unless you're trained to do so safely, and even then, it's a last resort measure.
If you're looking for a way to disable the vehicle, a more effective method would be to remove the car's key or disconnect the battery's negative terminal.
