As families endure a tense wait for news about their missing loved ones, authorities continue to unravel the tragic sequence of events behind the fire’s rapid spread. Meanwhile, experts diligently work to identify the victims, slowly piecing together the circumstances that led to this disaster.

Newly surfaced videos and eyewitness testimonies paint a grim picture, highlighting a perilous mix of factors: flammable ceiling materials and a bustling bar teeming with young patrons, all converging toward a narrow exit.

One particularly haunting video captures at least six bottles lifted high as smoke and flames suddenly consume the ceiling above.

The sparklers seem to have set off what specialists suspect is acoustic panelling on the ceiling, a substance designed for sound enhancement but notorious for its flammability.

Commenting on the situation, independent fire consultant Stephen MacKenzie likened the material to “plastic petrol,” noting, “That’s why we’re seeing reports of many young individuals suffering from first, second, third, and tragically, fourth-degree burns.”

Independent fire consultant Stephen MacKenzie described it as “plastic petrol,” adding: “That’s why we’re seeing reports of many of the young people with a first, second, third and unfortunately, fourth degree burns.”

Swiss chief prosecutor Beatrice Pilloud told reporters on Friday that investigators are examining the installation of foam panelling at the bar, and whether it complied with regulations.

Once the fire broke out, it spread quickly.

One video shows a young man attempting to put the fire out by hitting it with a cloth, while others record on their phones or continue dancing, seemingly unaware of the imminent danger.

“Once the ceiling was on fire, within about 10 seconds, the entire nightclub was on fire,” one witness said.

Another eyewitness, Axel, who did not give his surname, told Reuters news that he and others in the bar didn’t initially realise the danger was serious.

“We were yelling, ‘Fire! Fire!’ and then we thought it was a joke or that it wasn’t necessarily serious.

And then suddenly, a huge cloud of black smoke, we couldn’t breathe anymore,” he said, describing how he eventually got upstairs and smashed a window to get out.

As smoke filled the lounge and the fire blazed, partygoers rushed toward a narrow staircase.

Video verified by CNN shows dozens trapped at the exit, with one person jumping through a window as thick, red smoke engulfed the building.

MacKenzie explained the fire’s rapid spread through a process called a flashover, in which nearly everything in a room ignites almost simultaneously.

“Combustions pick up at ceiling level,” causing the fire to “spread laterally,” he said. This process is like a “stone drop in an ocean,” with smoke rippling out sideways and starting to “preheat” everything in front of it.

When the fire door was opened, it could have created a “chimney effect” which accelerated the flow of smoke and combustible gases upward, MacKenzie said. “The smoke is actually on fire, a ‘flashover,’” he added.

On Friday afternoon, Pilloud, the Swiss prosecutor, said all signs supported that theory.

“As things stand, everything points to the fire starting from sparklers or flares placed in champagne bottles that came too close to the ceiling, which very rapidly led to a flashover fire.”

Laetitia Place, a 17-year-old partygoer from Lausanne, recounted her harrowing escape from the fire, saying that there was a crush at the narrow exit that made it difficult for others to get through.

“The first stairs are pretty easy to get through since they’re wide and all that. But after that, there’s the small door where everyone was pushing, and so we all fell.”

“We were piled on top of each other, some people were burning, and some were dead next to us,” the teenager told Reuters.

Video obtained by CNN shows multiple people lying motionless outside, while bystanders try to help.

Resident Samuel Rapp, 21, witnessed that aftermath.

“There were people screaming, and then people lying on the ground, probably dead.”

Emergency services arrive

Edmund Coquette told CNN-affiliate RTL Germany that he saw “bodies on the streets,” and young people “totally burned in the face,” who were missing fingers.

A man living near Le Constellation, who ran to assist people fleeing the burning building, described searching for an emergency exit behind the bar and finding a jammed door with people trying to get out.

The man, Paolo Campolo, told French media outlet “20 Minutes” that he asked the fire captain for help but soon decided to intervene himself.

“We didn’t wait. With someone who happened to be passing by, we broke the door open and got the people out,” Campolo said from a hospital bed.

Dr Robert Larribau, head of emergency care at Geneva University Hospital, told CNN that most patients the hospital received were 15 to 30 years old, many with “extremely serious injuries” caused by flashover and possible backdraft.

Flashover typically causes severe burns, particularly on the face, back and upper limbs, often combined with critical inhalation injuries from radiant heat and superheated gases.

Backdraft, an oxygen-driven explosion, can cause instantaneous fatal burns and toxic inhalation.

An investigation has been opened into the circumstances surrounding the fire and how it spread so quickly, as Swiss officials said Friday that the two French owners of the bar have been interviewed by police to gather information.

Meanwhile, as of Friday evening, many loved ones of the victims and injured were still waiting for answers, and authorities continue the process of identifying the dead.