What is the purpose of the 'Emergency Fuel Cut-Off Valve' (Not-Kraftstoffabsperrventil) on a passenger bus?

1. To prevent unauthorized passengers from stealing fuel
2. To increase fuel flow during hill climbs
3. To switch between diesel and water
4. To mechanically or pneumatically cut off fuel supply directly at the fuel tank outlet in the event of an engine fire or severe collision, starving the fire of diesel fuel