How do crowd disasters like Indonesia's football tragedy happen and can they be prevented?

The deaths of at least 125 people in Indonesia on October 1 was one of the world's deadliest sporting stadium disasters in recent history.

For many, the tragedy was a stark reminder of the 1989 incident at Britain's Hillsborough Stadium, in which an influx of people caused a severe crush that left 97 football fans dead.

More recently, a crowd crush during rap star Travis Scott's Astroworld music concert in the United States killed at least eight people and injured dozens.

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The disasters are not always linked to high-energy sports events or music festivals - in 2015, at least 2,411 Muslim pilgrims died in a crush during the annual Hajj pilgrimage in Saudi Arabia and in 2008, 168 people were killed when thousands of Hindu pilgrims were caught in a panic at a temple in Jodhpur, India.

But what causes these major crowd disasters to happen? And how can they be prevented?

There is no one reason or cause behind a crowd disaster, but instead, a multitude of causes coming together at the same time, according to Ise Murphy, a crowd safety consultant for major sports events and large public events in the UK.

"It also doesn't come out of the blue, there is always a slow build-up before this happens," she added. "Often, if you look into a disaster timeline, and especially the cultural and economic background surrounding the event, there are always warning signs that indicate something like this might happen."

This might ring true for the disaster in Indonesia, where football is the most popular sport and the domestic league is widely followed. The sport also has a history of inciting strong passions and fanaticism that have led to brawls and clashes resulting in deaths in the past.

Officials knew there was precedence for conflict between fans of Arema FC and long-time rivals Persebaya Surabaya at the match in Indonesia on Saturday night. So, they took precautions such as increasing security presence and banning away fans from attending.

However, things started to go awry when home fans, disappointed by their team's loss, stormed onto the field and attacked players and football officials.

One of the primary causes for disasters is the fight-or-flight response triggered by a radical change in environment, such as the introduction of a noxious substance, according to Keith Still, a visiting professor of crowd science at the University of Suffolk and a specialist in crowd safety.

"Stampede is an incorrect word to describe what happened in the disaster," he said. "Fight-or-flight syndrome is a more appropriate description of what happened as the crowd was reacting to get away from the perceived or real threat.

"It is an entirely predictable reaction to the use of tear gas in that space."

The relationship between police and spectators is also an important consideration, according to Murphy. "The way the police dress, the modes of escalation they use can really impact the rapport between the police and the spectators, you want that to be positive."

World football's governing body Fifa has banned the use of tear gas as a crowd control measure.

Following the match, Amnesty International called for an investigation into why tear gas was deployed in a confined space, saying it should only be used "when other methods have failed".

When a group of people who are panicked or in pain are packed into a tight space, disasters like this are inevitable, according to Murphy.

"If you or I were in a crowd in a stadium and tear gas was thrown, we would be in pain, we would be scared, and we would want to get out," she said. "When people are rushing for those exits, they might all move towards the same direction."

"When you have anything over a density of more than five people per square metre, you're starting to put pressure on the human body. That increased pressure leads to asphyxiation and that inability to breathe is often the cause of death in these situations," she added.

Some of the world's largest crowd disasters have been linked to religious gatherings, where people are often congregated together.

"In particular religious events, people would want to do a special ritual, and so people might push forward in a limited area all at the same time," said Faisel Illiyas, a disaster risk management specialist for a World Bank-linked recovery project in India.

Often, people are very emotional in these situations and might not be considerate of their surroundings, he added. "It is very difficult to manage these events, so proper queuing mechanisms and crowd control measures need to be implemented specific to each ritual and event."

There needs to be a lot of work and planning done before an event to properly look into all the potential risks, and see how they can be avoided, Murphy said.

"A multi-agency approach is necessary. In the case of a stadium, you have the stadium managers, police and local authorities, the stewarding company, they all need to work together to assess what environmental and cultural risks are associated with the event, and what can be done to avoid potential risks," she added.

"Understanding the causes of previous disasters, and increasing education on how they occur is the best start to preventing them down the road," said Still from the University of Suffolk.

This article originally appeared on the South China Morning Post (SCMP).

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