Amanda Ripley in Time:
Most of the people who died on 9/11 had no choice. They were above the impact zone of the planes and could not find a way out. But investigators are only now beginning to understand the actions and psychology of the thousands who had a chance to escape. The people who made it out of the World Trade Center, for example, waited an average of 6 min. before heading downstairs, according to a new National Institute of Standards and Technology (NIST) study drawn from interviews with nearly 900 survivors. But the range was enormous. Why did certain people leave immediately while others lingered for as long as half an hour?