At my work we had our generators on the roof above 6th floor. It had a small tank that can run for a couple of hours. In the basement, a larger tank that had fuel for 2 days.
Sadly when the power went away, so did the power to the pump that were supposed to lift it to the root. So the our electrician all of the suddon got busy.
At another workplace we had two huge generators with flywheels for starting them, plenty of fuel and even our own redundant line to the powerplant some miles away. Sadly when the installation got upgraded, someone rewired the part that monitored the power coming in so it monitored itself. So after it had fired up and run for some time and synchronized the phases to itself. It shut down and we lost power again. That went on for the most of the day and almost drained our UPS batteries before they figured out what was wrong.
ah the memories.