Why did 21 people die at the Love Parade two years ago? The answer is interesting:
They say there is no evidence of a stampede in the form of a sudden rush of people at the place where the deaths occurred .
Neither is there evidence that intentional pushing caused the crush. And while there was good reason or individuals in the crowd to panic when their lives were in danger, there is no evidence that a kind mass hysteria was at work as a contributing factor.
So if the deaths did not occur near the staircase, which was the focus of many people's attempts to get away, where did they occur and why?
Helbing and Mukerjee say most deaths occurred elsewhere in the crowd because of a phenomenon known as crowd quakes. These occur when the density of a crowd becomes so great that individuals are forced into bodily contact with each other.
When this happens, the forces are transmitted through the crowd in chains from one body to the next. Crucially, when this happens, the transmitted forces add up.
This transmission of force is similar to the way force chains occur in a granular material like sand. In fact, at times groups of individuals in such a chain can become jammed, like grains of sand that jam as they pass through an hour glass.
The whole paper is here (pdf). A collection of amateur videos which the researchers used in their study, can be found here. The website warns you that some of the images are graphic, but what it doesn't warn you is that GEMA has blocked some of the videos! Our benevolent overseers strike again...