By Kara Fox, Thomas Bordeaux, Lou Robinson, CNN
(CNN) — As young partygoers rang in the New Year at a packed bar in the Swiss Alps, the celebrating quickly turned into a nightmare when a devastating fire tore through the basement, killing at least 40 people and injuring 119 others.
The blaze at Le Constellation in Crans-Montana has been described by Switzerland’s president as one of the country’s “worst tragedies.” As families anxiously await word about missing loved ones and experts work to identify the victims, authorities are still piecing together how the fire started and why it spread so fast.
Swiss authorities said Friday that the champagne sparklers were the likely cause of the fire, though the official inquiry remains ongoing. Emerging videos and eyewitness accounts reveal a deadly combination of hazards: fire-prone ceiling paneling and a crowded bar packed with young patrons funneling toward a narrow escape route.
A night of revelry
Le Constellation, located in the heart of Crans-Montana, a luxury sky resort in the French and German-speaking canton of Valais, is a popular nightspot among young locals and visitors.
Around 200 people were inside the venue on New Year’s Eve, according to eyewitnesses, ready to celebrate 2026 with music, drinks and dancing.
Sparkles that turned to smoke
Imagery widely shared online show staff in motorcycle helmets perched on others’ shoulders, holding champagne bottles with sparklers amid the packed crowd.
One clip shows at least six bottles raised in the air as flames and smoke erupt from the ceiling.
The sparklers appear to have ignited what experts believe is acoustic paneling on the ceiling, a material designed to improve sound but that can also be highly flammable.
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 looking into the installation of foam paneling at the bar, and if it complied with regulations.
A fast-spreading fire
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.
Horrific escape
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.”
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