Against the speculation that third tower at WTC had fallen because of explosives kept inside, a new investigation report reveals that it collapsed because of fire caused by the debris from falling twin towers. Twin towers were located just 400 ft away from it, and falling debris damaged structural columns and ignited fires on at least 10 floors at 7 World Trade Center.

 

Leading investigator, S. Shyam Sunder (National Institute of Standards and Technology) said that subsequently, these fires might have been fed partly by the diesel from tanks and a pressurized fuel line in the fifth to the ninth floors. Also, the same fire according to the investigators must have been fuelled by office paper and furnishings.

 

Accordingly, the collapse started when a girder on the 13th floor disconnected from a critical column which supported a long open floor span. And, once that floor gave way to flows fifth floor too collapsed. The building housed a branch office of the CIA, the Secret Service and New York mayor's emergency operating office. However, there was no casualty as people were evacuated before fire could break in.