As Houston police and the FBI investigate Friday's deadly Astroworld concert, some experts are questioning what role, if any, having only one stage operating during Travis Scott's prime-time performance may have played.
By the time Scott took the main stage Friday evening, most of the thousands of fans at the event had gathered as close to it as they could, concertgoers have said.
The chaos unfolded shortly after 9 p.m. when the crowd began to "compress" toward the front of the stage, officials have said. Houston Police Chief Troy Finner has said a few people started "going down" at 9:30 p.m. Officials told producers what was happening, and the show ended at about 10:10 p.m., he said.
The crush, which killed eight people and injured hundreds of others, coincided with the start of Scott's set.
"That sounds pretty scary," said Keith Still, a crowd science expert in the United Kingdom. "If you have a multi-stage setup, you would assume people would be distributed among stages."
Scott's set started after SZA wrapped up on the second stage, which then went dark for the evening. The top-of-the-bill appearance by Scott, Houston's native son, was alerted by a countdown and lit up by pyrotechnics, and it included a surprise appearance by the star rapper Drake.
The main stage was the place to be — and it was essentially Astroworld's only place to be once Scott stepped out.
The event's two-stage setup was to have been used as a crucial crowd control measure, Houston Fire Chief Samuel Peña said Saturday at a news conference.
"Part of when we have large events, one of the things that we consider is to ensure that the crowds are subdivided," he said. "They had two separate stages in two separate areas. That was part of the plan."
But to be effective, alternate stages at festivals must be used, concert promoters say.
"If you've got favorable artists on different stages at the same time, then the crowd will be split," said Reza Gerami, a veteran Los Angeles festival promoter. "You've got to have secondary options for stages and other talent."
But Scott had the only spotlight Friday night.
"Once Travis Scott came on, I told myself this is the moment I've been preparing for, I just need to breathe," said witness Diana Amira, 19. "But ... my rib cage was so squished that I couldn't expand my lungs to catch a breath."
Scott said in the Instagram story on his account Saturday that he was "devastated" by the deaths and the injuries.
"I could never imagine anything like this just happening," he said. "My fans really mean the world to me, and I always just really want to leave them with a positive experience. Any time I can make out ... anything that's going on, I'd stop the show and ... help them get the help they need."
He added that he could "never imagine the severity of the situation."
Often, large music festivals will use alternate stages and exhibits to draw at least some fans away from major headliners. In addition to being crowd control safety measures, they help producers create the artistic mix that has become a hallmark of the festival experience.
Fort Lauderdale, Florida-based safety consultant Scott Atlas noted that many festivals feature staggered schedules on multiple stages so crowds don't all move at once. "You want to disperse the crowd a little bit," he said.
It's not clear whether the festival setup and the stage scheduling are part of the investigation.
Police and fire officials didn't respond to requests for comment, and neither did the festival's organizer, Live Nation, or the venue and security manager, ASM Global.
Nina S. Jackson, a spokesperson for the venue, NRG Park, a Harris County-owned complex in Houston, declined to comment, citing pending litigation and ongoing investigations.
Peña, the fire chief, said Saturday that the event "was limited to 50,000" and that the location could have handled thousands more people.
"They could have had over 200,000 people in this venue," he said.
Rafael Lemaitre, a spokesperson for Harris County Judge Lina Hildago, said the maximum capacity for the space is 240,000 people. (County chief executives are called "judges" in Texas.)
Experts say such a number is based on a ground-space formula that doesn't necessarily consider police, security, EMTs, stages or concessions or how the crowd would move from place to place.
"It doesn't matter what the space is," said Still, the crowd science expert. "It's how that space is utilized."
Peña said Saturday that investigators were focusing on whatever "incidents" might have sparked the panic.
"What we're looking into is what caused the crowd surge, what led to the crowd surge and those incidents at the point of where the concert was looking at the stage," he said.