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Strategically Placed Obstacle Near an Exit Can Speed Evacuations

Limiting the number of pedestrians that approach an exit at once can have beneficial effects, a study finds



©iStockphoto/Lars Christensen

If you find yourself in a crowded building during an emergency, perhaps the last thing you want to see is an obstructed exit. But a new study by a group of Japanese researchers shows that wide-open exits are not always the most efficient at speeding pedestrians through. A judiciously placed obstacle, such as a column, can actually reduce bottlenecking and evacuation times.

Daichi Yanagisawa, a graduate student in the School of Engineering at the University of Tokyo, and his colleagues examined various ways of reducing conflicts—friction, essentially—between individuals as they try to squeeze through an exit.

In research set to appear in the journal Physical Review E, Yanagisawa and his co-authors tested various theories using a model incorporating both the friction of conflicting pedestrians and the slowing effects of obstacles that they must circumnavigate. The researchers also ran evacuation drills with 50 human subjects working toward a narrow exit.

The research team found that the problem with wide-open spaces in front of exits is that evacuees can approach from all sides, allowing the maximum number of pedestrians to enter into conflict at the exit. Reducing exit access with an obstacle can pare down the severity of those conflicts. "When a proper obstacle is set up at an appropriate position in front of the exit," Yanagisawa says, "it blocks a pedestrian moving to the exit and decreases the number of pedestrians moving to the exit at the same time."

Not just any old obstacle will do, of course. Yanagisawa notes that its size, shape and orientation has to be tailored to the space and to the width of the exit itself. In general, however, off-center obstacles are more effective than those placed directly in front of an exit. "When an obstacle is set up at the center of the exit," Yanagisawa says, "it makes pedestrians detour and slows down the evacuation." An obstacle placed to one side, on the other hand, "decreases the probability and the impact of conflicts without making pedestrians detour a lot," he explains.

Andreas Schadschneider, a professor at the University of Cologne's Institute of Theoretical Physics in Germany who has studied pedestrian and traffic flows, says that the obstacle effect has popped up occasionally in the literature for several years. But the new work is, to his knowledge, the first time it has been empirically tested. "So, it no longer remains a vague theoretical prediction, but should be considered a serious effect that might be used for substantial increase in the safety of sports arenas and other large public buildings," Schadschneider says.

He adds that even empirical tests with human subjects cannot fully replicate the conditions of an evacuation, however. For one thing, real-world evacuees might be discouraged by the appearance of an obstacle and retreat toward a different exit, which could negate the obstacle's benefits. Real evacuation simulations are extremely difficult to carry out and can be extremely dangerous, Schadschneider says, pointing to a 2006 test of Airbus's A-380 aircraft in which one subject suffered a broken leg and dozens of others sustained lesser injuries.

The researchers also note that their model does not yet compensate for the intelligence of real-life pedestrians, and Yanagisawa cautions that the new results do not imply that building managers should start blockading fire exits. The findings, he says, merely suggest that researchers should start to "consider installing obstacles as one option which holds potential to shorten a total evacuation time."

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