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Zedeño still did not immediately flee on 9/11, even after her colleague screamed at her. First she reached for her purse, and then she started walking in circles. "I was looking for something to take with me. I remember I took my book. Then I kept looking around for other stuff to take. It was like I was in a trance," she says, smiling at her behavior. When she finally left, her progress remained slow. The estimated 15,410 who got out, the NIST findings show, took about a minute to make it down each floor--twice as long as the standard engineering codes predicted. It took Zedeño more than an hour to descend. "I never found myself in a hurry," she says. "It's weird because the sound, the way the building shook, should have kept me going fast. But it was almost as if I put the sound away in my mind."
Had the planes hit later in the day, when the buildings typically held more than 32,000 additional people, a full evacuation at that pace would have taken more than four hours, according to the NIST study. More than 14,000 probably would have perished, Zedeño among them.
In a crisis, our instincts can be our undoing. William Morgan, who directs the exercise-psychology lab at the University of Wisconsin at Madison, has studied mysterious scuba accidents in which divers drowned with plenty of air in their tanks. It turns out that certain people experience an intense feeling of suffocation when their mouths are covered. They respond to that overwhelming sensation by relying on their instinct, which is to rip out whatever is in their mouths. For scuba divers, unfortunately, it is their oxygen source. On land, that would be a perfect solution.
Why do our instincts sometimes backfire so dramatically? Research on how the mind processes information suggests that part of the problem is a lack of data. Even when we're calm, our brains require 8 to 10 sec. to handle each novel piece of complex information. The more stress, the slower the process. Bombarded with new information, our brains shift into low gear just when we need to move fast. We diligently hunt for a shortcut to solve the problem more quickly. If there aren't any familiar behaviors available for the given situation, the mind seizes upon the first fix in its library of habits--if you can't breathe, remove the object in your mouth.
That neurological process might explain, in part, the urge to stay put in crises. "Most people go their entire lives without a disaster," says Michael Lindell, a professor at the Hazard Reduction & Recovery Center at Texas A&M University. "So, the most reasonable reaction when something bad happens is to say, This can't possibly be happening to me." Lindell sees the same tendency, which disaster researchers call normalcy bias, when entire populations are asked to evacuate.
When people are told to leave in anticipation of a hurricane or flood, most of them check with four or more sources--family, newscasters and officials, among others--before deciding what to do, according to a 2001 study by sociologist Thomas Drabek. That process of checking in, known to experts as milling, is common in disasters. On 9/11 at least 70% of survivors spoke with other people before trying to leave, the NIST study shows. (In that regard, if you work or live with a lot of women, your chances of survival may increase, since women are quicker to evacuate than men are.)