One way to avoid water condensation and also reduce fire risk is to have the exhaust of the engine piped back to the fuel tank so that it replaces air. With careful design, the exhaust arriving at the tank will be cool enough for fire safety, but it may be set up to contribute to the warming of the fuel. In cold weather, diesel fuel thickens faster than gasoline, and fuel tank heaters will be needed in cold climates. Any additional heat source reduces the power needed for tank heaters.

Tank, generator and battery placement

Lessons about locations for fuel tanks came from both Sept. 11, 2001, and the hurricanes. Without touching the various conspiracy theories touring the Internet, it is clear that having the fuel tanks for the emergency generators on the roof of World Trade Center building 7, which housed New York's Emergency Operations Center, did not contribute to continuing operations when oil cascaded down but instead added to fires.

Other issues may keep the diesel generators from working. If the tanks simply have a spark-shielded vent to let air come in to fill the space created as fuel is used and the vent is covered with floodwaters, water will be sucked into the tank. Tanks with an exhaust return can be engineered to work underwater.

Remember that the diesel generators and their tanks can be a significant distance apart, as long as fuel can be pumped by the available pump motors, and that there is a proper method of getting air or exhaust into the tanks to avoid suction locks.