Physicists hope ideas help manage panicky crowds


Monday, October 2nd 2000, 12:00 am
By: News On 6


By Sue Goetinck Ambrose / The Dallas Morning News

In case of emergency, walk, don't run. And think, don't just follow.

That's what physicists have prescribed to escape a crowded room or stadium with fewer injuries.

Several times a year, somewhere in the world, people are trampled or crushed to death at stadiums, concert halls or other crowded gatherings.

Although many venues meet regulations for a safe evacuation, the regulations don't necessarily account for the quirks of human nature, said Dirk Helbing, a physicist at the Dresden University of Technology in Germany.

In the latest issue of the journal Nature, he and colleagues Illés Farkas and Tamás Vicsek from Hungary report on computer programs that mimic panicked crowds trying to escape various situations. Dr. Helbing says he hopes engineers will try to put his ideas to use to make crowded events safer.

At first glance, it sounds difficult to mimic people's behavior on a computer program. After all, people often act unexpectedly.

But Dr. Helbing has found that people are actually pretty predictable.

"Pedestrians are most of the time acting and interacting quite automatically," he said. "That's why we can use these physical equations."

To make the computer simulations, the scientists first collected media reports of panic situations. They found that often, people don't use all available exits in a building, but only a few. When that happens, building safety guidelines that assume all exits will be used equally become useless, he said.

Also, people get nervous and don't think for themselves.

"Nervous people start to do what other people do," Dr. Helbing said. "They think the best thing is to do what the majority of others are doing."

That's not always smart, he said.

"If there is no one who knows the right way to the exit, like if it's smoky or dark, then this herding instinct can have terrible consequences."

The computer simulations showed that in the simplest situation – where many people had to leave a room through a single exit – walking quickly through the door caused many problems.

Initially, a crowd forms and fills a semicircular region outside the door. Flow through the door stops for some time, and when the semicircle breaks up, groups of people leave the room at the same time. The flow of people is irregular and inefficient, Dr. Helbing said.

Part of the problem is that people try to walk faster. That puts them closer to other pedestrians, and people start brushing against each other, slowing movement.

"People are trying to get out faster, but as a consequence they get out slower," he said. "This is really tragic because they decrease their chance of survival by rushing."

Widening an escape route can also cause problems if the route narrows later on, Dr. Helbing found. When people try to squeeze into the main flow after the widened area, progress is slowed because too many people are bumping into each other. And if people begin to fall, they create obstructions that slow progress even further.

It doesn't take many people to produce deadly force, Dr. Helbing said.

"Fifty people pressing from behind produce a pressure of one ton," Dr. Helbing said. "If you've been in such a situation, you can't keep your feet on the ground and cannot control where you move. You can just try to keep your balance."

A pressure of four tons can break brick walls or steel barriers, he said.

Besides offering simulations of fatal scenarios, the scientists also offered a possible solution. They found that placing a column in front of an exit door can decrease the risk of injury by crushing. The column absorbs pressure from behind, easing pressure on people passing through the door. The column works best if placed asymmetrically with respect to the door opening, he said.

The simulations of panicked crowds, and descriptions of crowd disasters, are available on the researchers' World Wide Web site, angel.elte.hu/~panic.

It would be ideal for engineers, said Peter Molnar of Clark Atlanta University in Atlanta, if scientists could calibrate Dr. Helbing's computer simulations to more precisely imitate crowd behavior. Scientists have done that to study traffic flow, Dr. Molnar said, by taking videos of automobiles and entering the data into a computer.

But doing the same for people is more difficult. Video technology for tracking large numbers of people isn't available, he said.

If that data existed, engineers could design buildings with more confidence.

"In the future, it would be great," Dr. Molnar said. "We would have a software that designs the lobby of the building, and puts estimated pedestrian traffic in there. We could create a simulated panic."