On 24 July 2010, 21 people were crushed to death at the entrance to a festival known as the Love Parade in Duisberg, Germany.

Various experts have analysed this disaster and identified numerous failings that contributed to the disaster. Among them the decision to route all visitors, both leaving and arriving, through a single entrance tunnel that turned out to have a bottleneck that limited the flow of people in a way that was not properly accounted for.

Today, Dirk Helbing and Pratik Mukerjee reveal their analysis of the events leading up to the tragedy. Helbing is one of the world’s leading experts on crowd dynamics so his views hold some weight.

Their conclusion is also that the disaster was a complex event with many contributing causes. However, what’s unusual about this report is that Helbing and Mukerjee go to some length to show that certain factors and behaviours didn’t cause the disaster.

In particular, these guys focus on crowd behaviours such as mass panic, stampeding and intentional pushing, factors that have been widely discussed in the media as causes of the disaster.

Much of the media coverage focused on people attempting to escape the crush via a staircase that led away from the area.

But Helbing and Mukerjee say that most of the deaths did not occur here. And although there was undoubtedly severe crushing at this point, this was periodically relieved.

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.

This kind of jamming can cause the forces to build up to lethal levels. What’s more, these chains can suddenly break sending pressure waves through the crowd.

And this is what kills: not the overall density of the crowd but the transmission of lethal force through the crowd in ways that are almost random. This causes people to fall, creating a domino effect that crushes people to death.

An interesting corollary is that their analysis relies in large part on publicly available video footage of the disaster taken by members of the public at the time. Helbing and Mukerjee have assembled this into a webpage that gives a macabre overview of events. The webpage is here but be warned: it makes for shocking viewing at times.

They say that this kind of publicly available media could greatly contribute to the understanding of disaster like this and how to prevent. By contrast, most videos of previous crowd disasters are not public and not accessible to most researchers wanting to study it.

That gives them good insight into the disaster itself. However, they are on less sure ground when they discuss the allocation of blame for the tragedy.

Helbing and Mukerjee say: “The systemic nature of many crowd disasters makes their legal handling very difficult, since it is hard to determine the fraction of responsibility that different people and institutions had.”

The complex interaction between these people and institutions is itself a contributing factor to the disaster. In fact, Helbing and Mukerjee go further. They say they are convinced that the division of responsibility itself is the problem, and that this calls for political and regulatory attention.

And they issue a challenge: “Scientists could perhaps make a major contribution to the cultural heritage of humanity if they managed to find new ways to address this fundamental problem.”

Perhaps. Alternatively, it may be that we live in a complex world in which complex events will always occur. We can certainly hope to hold events and create institutions and perhaps entire industries that are robust against most types of disaster.

But the goal of eliminating disasters altogether or designing events in a way that leads to a clear allocation of blame afterwards, seems a goal too far.

Ref: arxiv.org/abs/1206.5856: Crowd Disasters as Systemic Failures: Analysis of the Love Parade Disaster