The inertia switch is the closest thing to a fuel shutoff switch. It's typically located under the dashboard, often near the driver's side, but its exact location can vary slightly. You might find it under the dash, near the steering column or under the carpet. It's a small, usually red, rectangular box that resets by pushing a button. This switch cuts the fuel supply in a collision to help prevent fires. If your car has been in an accident, check this switch.
There is no other easily accessible, manual switch to cut the fuel flow. To completely stop fuel flow in a non-collision emergency, you'd need to disconnect the fuel pump relay (this requires some mechanical knowledge).