The federal agency investigating the September 11, 2001 terrorist attacks on the World Trade Center says it was likely fire, and not the impact of the hijacked planes that crashed into the twin towers, that caused the buildings to collapse.
The National Institute of Standards and Technology issued that finding in an interim report Friday on its building and fire investigation of the World Trade Center.
NIST also says the original team that designed the twin towers may have underestimated the force the wind exerted on the World Trade Center.
In addition, the report says it would have taken four hours to evacuate the World Trade Center if the twin towers had been filled to capacity at the time of the tragedy. Investigators estimate there were between 16,000 and 18,000 people in the towers on September 11.
NIST is expected to issue its final report in December. It will include recommendations on how to better equip buildings to handle catastrophic events and improve evacuation methods.
