The death toll in 1990 was over 1,400. It was 270 in 1994, 118 in 1998 and 251 in 2004. Hundreds of people crushed, trampled and choked to death. Anders Johansson knew Mecca the way every prospective panic researcher gets to know the city: in terms of casualty numbers.
It is Jan. 12, 2006 and Johansson is experiencing the reality behind the statistics at first hand. He has travelled to Mecca on the invitation of the Saudi Arabian Ministry of Municipal and Rural Affairs. Johansson is here to study the flow of pilgrims -- the subject of his dissertation at Dresden University of Technology.
As the sun reaches its zenith, Johansson watches a sea of colored dots on a monitor. The dots are pilgrims dressed in white robes, on their way to the three pillars in a valley outside Mina, several kilometers from Mecca. The pillars symbolize the devil, who will now be ceremonially stoned. It is here that Abraham is said to have once chased the devil away by throwing stones. These days, the area is under video surveillance.
Around 11:53 a.m., the pilgrims at one of the entrances to the area begin pushing each other about. The crowd forces its way forward. At 12:19 a.m., the flow of pilgrims is stalled, and at 12:30 a.m. a gap forms suddenly in the midst of the crowd. Some of the pilgrims have fallen to the ground and others are stumbling over them.
Anders Johansson senses what is happening at this moment and has to sit down. He knows that when so many people crowd together, the body is exposed to pressure equivalent to more than one ton -- the weight of a small car. Tragically, the 2006 stoning entered the annual statistics with a total of 364 deaths.
When Anders Johansson returns to his office at the Dresden University of Technology a few days later, he is carrying video tapes in his luggage: films of people pressed closely together and forcing their way forward. Now he must examine the cause of the catastrophe. He does not have much time. The next pilgrimage will begin on Dec. 28, 2006.
After the mass panic on Jan. 12, authorities had had enough. They resolved to regain control of the growing streams of pilgrims and sought advice from Dirk Helbing of the Dresden University of Technology.
Helbing, a youthful six-footer, is a pioneer in the field of panic studies. His scholarly articles on the flow of pedestrians and cases of stampedes in football stadiums are the most frequently quoted within the field.
Helbing put together a team of German experts for the Saudis, comprised of traffic planners from Aachen, logistics experts from Dresden and his doctoral student Anders Johansson. For Helbing, Mecca is "the biggest pedestrian problem in the world."
Every Muslim is required to make the pilgrimage to Mecca once in his life in order to prove his obedience to God. The pilgrimage, known as the hajj, takes place every year on five days during the last month of the Islamic lunar calendar. The Prophet Muhammad originated the hajj tradition in the seventh century. First, hundreds of Muslims came -- then thousands, then tens of thousands. By January 2006 the number had climbed to 3 million.
That makes Mecca, the place of redemption, a place of risk. Nowhere else in the world do as many people crowd onto as small an area. The valley at Mina is about three kilometers by three kilometers (1.9 miles by 1.9 miles) large. Every year, it's as if Berlin's entire population were to converge on the city's Schönefeld airport.
The pilgrims arrive from more than 100 different countries. For most, it is the first time they have flown in an airplane. They land at Jeddah airport by the Red Sea, which opens a special terminal during the hajj. Hundreds of thousands of them are illiterate, and they speak dozens of different languages. In some of their countries of origins, the custom is to walk on the right side of the street; in others, the custom is to walk on the left. The situation involves "many uncontrollable variables," Dirk Helbing notes soberly.
Researchers have learned from computer simulations that people who want to escape from a room may block each others' way in a phenomenon known as "escape panic." When those at the back push and the exit at the front is blocked, people are crushed to death. But the case in Mecca presented the scientists with a puzzle: People have died even in open areas there.
In order to evaluate the 2006 videos, Anders Johansson developed a computer program to count the pilgrims. When people crowd into a subway or an elevator, three or four of them can fit onto one square meter (10.8 square feet). In scenarios developed by researchers studying pedestrian behavior, based on the size of the average European, the maximum density was six people per square meter. In Mecca, the number per square meter was 10.
Helbing and Johansson scanned the video material for early warning signals announcing the start of a mass panic. When they viewed the film at 10 times the normal speed, they found what they were looking for: Twenty minutes before the catastrophe, the first patterns of irregular movement appeared in the crowd, which had previously been flowing at an even pace. Shortly before the catastrophe, blocks of hundreds of people suddenly began jerkily drifting in every direction. What had appeared fluid just a moment before was now behaving "like the earth during an earthquake," Helbing explains. Crevices appear between blocks of people. Some people lose traction. Those people who fall down may never stand up again.