What is the purpose of the 'Emergency Stop Switch' (Batteriehauptschalter / Not-Aus-Schalter) located near the driver's dashboard on passenger buses?

1. To eject the passenger luggage
2. To turn off the windshield wipers
3. To deflate the tires
4. To instantly disconnect the main 24V electrical battery circuits from the entire vehicle in an emergency (fire, collision, short-circuit), preventing electrical fires and fuel ignition