These are the warning signs that a crowd is dangerously dense

(CNN) –If you are in a crowd and people are close enough to bump into you, there may be too many people.

That’s according to G. Keith Still, Visiting Professor of Mass Science at Suffolk University and Director of GKSkill International, a consultancy that trains event organizers on how to spot hazards.

Still has been studying crowd behavior and safety dynamics for 32 years, and while he was unable to speak directly about the tragedy at the Houston Astroworld Festival, he said organizers can help prevent crowd-crushing incidents by monitoring the crowd. crowd density in real-time conditions and regulate the flow of people to a place.

The density of the crowd can be calculated in number of people per square meter. Younger and smaller people take up less space than older and larger people, but, as a general rule, things get awkward once you hit five people per square meter, Still said, and anything with more people can become dangerous.

“When bodies touch, that high energy and density can lead to these avalanches and human collapses,” Still said.

One sign that the crowd has become too dense is what Still called a “wheat field effect,” where people sway uncontrollably. He said that you can see an example in the videos online from a 2005 Oasis concert in Manchester, England, just before a huge stampede of people rushed onto the stage.

Keeping people safe means being able to detect when a crowd is getting too dense, but that’s trickier than it sounds. Among other things, he said, it depends on the viewing angle, say from a helicopter or a stage.

The key to preventing a disaster, Still said, is for organizers to watch the density and, if it starts to increase, slow or stop the flow of people entering the area. He said it is much more difficult to reduce overcrowding once the situation has become too dense.

If a venue gets too crowded, Still said, artists should stop and ask everyone to step back. Over the years, various artists, including A $ AP Rocky and Linkin Park, have done exactly that.

Following crowd-related disasters such as a 1989 Hillsborough football stadium collapse, a 2003 Station nightclub fire, and a stampede at the E2 nightclub, the same year, many jurisdictions adopted crowd-related regulations and required licensed “crowd managers” to be on site and enforce safety rules.

A 56-page plan of operations for the Astroworld event, obtained by CNN, includes a section on “incident management” that reads: “The Festival employs experienced and licensed event security to assist with crowd management and security at the scene of an incident “. Another section reads: “Crowd management techniques will be employed to identify potentially dangerous crowd behavior in its early stages in an effort to prevent riots or civil unrest.”

If you’re in a crowd, Still said you can help keep yourself safe by keeping an eye out for areas that are likely to be the busiest and fighting your way through the crowd if you don’t have enough personal space.

Amy Hoy, who produces festivals and events as the senior vice president of Deep South Entertainment, said she has a simple rule of thumb for crowd events. “Personally, for me it’s: can I put my hands on my hips comfortably without touching anyone else?”