The Problem with Backup Power
The collapse of Seven World Trade Center (remember that?) may have been caused by a fire fed by the fuel tank for backup power:
As engineers and scientists struggle to explain the collapse of 7 World Trade Center, they have begun considering whether a type of fuel that was inside the building all along created intensely hot fires like those in the towers: diesel fuel, thousands of gallons of it, intended to run electricity generators in a power failure.
One tank holding 6,000 gallons of fuel was in the building to provide power to the command bunker on the 23rd floor. Another set of four tanks holding as much as 36,000 gallons were just below ground on the building's southwest side for generators that served some of the other tenants.
Engineers said that here and across the country, diesel-powered generators are used in buildings like hospitals and trading houses, where avoiding power outages is crucial. Partly for that reason, Jonathan Barnett said, a definitive answer to the question of what happened in 7 World Trade Center is perhaps the most important question facing investigators.