Crowd disasters, like the 2010 Love Parade tragedy in Germany, are often caused by uncontrolled collective motions. At that event, sadly, 21 people died in a stampede.

Now, they do. In the middle of the dense crowd, you can barely hear XCX’s vocals over the crowd’s thunderous vocals, singing “I don’t care / I love it” over and over again.

This happens when a crowd becomes so dense that its very nature changes. “When a crowd gets to a density of more than five people per square meter, it starts acting as more like a liquid than a ...

The crowd is so dense that it would be like fitting 900 people in a one bedroom apartment. And, as festival goers cheers and sways, the movement looks like ripples of water. Denis Bartolo is a ...

Videos posted online show a gray minivan plowing into the dense crowd, sending people flying into the air and dragging others under the vehicle. When the van came to a stop, the crowd charged at ...

CHANG: Yeah. BARBER: The density of this crowd is comparable to, like, putting 900 people in a one-bedroom apartment. And they are - they're, like, kind of moving like water.

To accurately capture crowd density, then can use grid-sampling, as in the Jacobs Method. Most analysts recommend using a combination of approaches to ensure an accurate estimate.

CHANG: Yeah. BARBER: The density of this crowd is comparable to, like, putting 900 people in a one-bedroom apartment. And they are - they're, like, kind of moving like water.

When the crowd density was beyond this threshold, the local density varied tremendously — reaching up to nine people per square metre in some places.