Imagine that the dead have risen from their graves. They’ve gotten into a building you’re hiding out in. You slink down the hallway and enter what you think is a safe room.
It’s empty, and looks like a good place to hide. As you stand in the middle of the room, you look around. There’s only two doors: the one that you came through and one on the opposite side of the room. You should be able to barricade them both with furniture. But, oh no! The zombies have found the room, too. They’re shambling around both doors, with more crowding the doorway you just used, and now you have to get out. Which door do you exit through?
The less crowded one, I’m sure you’re saying. Of course, that makes the most sense. If both doors are the same distance from where you’re standing, why not use the one that’s got fewer obstacles?
Well, science has some bad news for you: You’ll probably wind up as a snack for the living dead, or at least stuck in a crowded doorway. Stress makes us do stupid things, like seek familiar routes even if they’re not the best ones. Over and over, eyewitness reports from real-life evacuations have suggested that, in emergencies, people tend to exit buildings from the main entrance that they used to enter the building, ignoring one or more emergency exits along the way. The crowding at these entryways slows evacuation times and sometimes results in injuries and even deaths.
Earlier this year, the Science Museum of London held a zombie-themed science festival called “ZombieLab.” Researchers Nikolai Bode and Edward Codling, from the University of Essex, took advantage of the event to look at the decisions people make in emergencies. They set up a computer simulation of a room evacuation similar to what I described above. One hundred and eighty-five museum guests took control of a computer person in a virtual environment filled with 80 virtual zombies.
At the start of the experiment, the participants just had to move their person from the hallway and into the central room. Next, they had to move back out again, through one of two doors, to where they started in the hall. During this second part, the researchers presented the visitors with a few different conditions. Some just had to simply exit the room. Others were encouraged to beat the fastest exit time. Others were presented with a crowd of zombies split unevenly between the two exits. A last group had to deal with the crowed exits while trying to beat the best time.
In the normal exit scenario and when they were trying to set the best time, the museum visitors split evenly between the two exit routes and showed no clear preference for one or the other. Faced with zombie-crowded exits, though, the visitors started to show some bias for the doorway they had come through, even if it was more crowded. Presented with the zombie obstacles alone, some of the visitors went for they door they came through, and then changed their mind when they realized how crowded the doorway was. With the added pressure of the time clock, fewer people changed their mind and stuck with trying to get out that exit, even though it was the slowest route.
Bode and Codling’s results fit with what other researchers have found in theoretical models and real-life evacuations. Under stress, people make irrational decisions. Here, the museum visitors under pressure to exit quickly were more likely to stick to the route they knew even if it wound up taking them longer to get out, and were less likely to change their mind and adapt to the situation.
In a real-world situation, the researchers say, their results suggest some strategies for minimizing risks during stressful evacuations. One idea they offer is having people in large, crowded buildings enter from several different locations. If they have to get out quickly, and their preference for the way they came in holds up, they’ll spread out to different routes and avoid overcrowding any one exit.
It’s worth mentioning that the idea that the other virtual characters in the room were zombies was just meant to fit the experiment in with the theme of the festival and keep participants blind to the purpose of the experiment. In the simulation, the zombies didn’t attack participants or pose any danger, but simply blocked the doorways. The study participants didn’t have to treat them as a threat, so they focused on choosing one door or the other without worrying about getting their brains eaten. I wonder if, or how, the results would differ if the “zombies” acted more like zombies, and how decision-making in an evacuation is affected if there are obstacles at exits that pose active threats.