What images and videos tell us about why the Swiss bar fire spread so quickly

Investigators are racing to determine how and why a deadly New Year’s Eve fire at a Swiss ski resort bar spread so quickly.

Authorities said at a news conference Friday that sparklers attached to champagne bottles which took place “too close to the ceiling” seem to have started the fire in the cellar of the Le Constellation bar in Crans-Montana.

But the manner in which the fire spread with such ferocity, killing at least 40 people and injuring 119, many seriously, is now a major concern for authorities, as is the bar’s safety record.

​​BBC Verify examined videos taken by survivors and bystanders and spoke to fire safety experts to find clues as to what went wrong.

Two striking images widely shared online show people carrying bottles of champagne with lit candles above their heads, surrounded by a crowd.

One image shows flames beginning to build up on the ceiling above people holding five of these bottles in the air.

The second image is a closer angle, showing a person wearing a helmet and holding a bottle with a lit sparkler, sitting on the shoulders of another person wearing a Guy Fawkes mask.

The sparkles from this bottle seem to be closer to the ceiling.

​​BBC Verify determined that these images were taken after midnight on January 1 by confirming that no earlier versions existed and compared them to public photos of the Constellation – using details such as the bar design and distinctive plumbing.

And there was no evidence that the images had been manipulated using artificial intelligence (AI).

In other videos we checked from the night of the fire, some people in the bar can be seen filming the flames as loud music from the club blares in the background. In one video, some people begin running toward an exit stairwell, screaming.

On Friday, Béatrice Pilloud, attorney general of Valais, said that everything led investigators to believe that the fire started from sparklers attached to champagne bottles “too close to the ceiling”.

Emphasis is also placed on the foam padding of the bar ceiling and its compliance with safety standards.

Two fire safety experts told BBC Verify that materials visible in photos and videos of the Constellation appeared to show “egg carton foam”, a type of sound-deadening material made from polyurethane (PU).

In the photo of the brandished bottles, flames are visible on a part of the ceiling covered with foam covering.

PU foam is often treated with a fire retardant before being installed as a noise dampener in factories and entertainment venues.

But if left untreated, it can be highly flammable.

“Once ignited, polyurethane acoustic foam can exhibit rapid flame spread over its high surface area and produce dense, toxic smoke, significantly accelerating fire growth and reducing available evacuation time,” said Dr Peter Wilkinson of Loughborough University.

Professor Edwin Galea, from the University of Greenwich, said the effectiveness of the retardant treatment on PU foam can fade over time.

Swiss authorities say they cannot confirm what type of foam padding was used in the bar or whether or not it complied with safety standards.

At Friday’s press conferenceofficials spoke of a “flashover” occurring in the bar.

Professor Galea explained that this is what happens when hot gases rise to the ceiling, reach a critical temperature and then ignite the room almost instantly.

According to Michael Klippel, fire safety expert at ETH Zurich, “survival after a flashover is very unlikely.”

The authority responsible for supervising fire safety inspections in Crans-Montana is the Office Cantonal du Feu (OCF) of the Canton of Valais. Inspections are carried out by local agents.

Swiss authorities told a news conference that inspections on a vessel the size of the Constellation should have been carried out every year.

BBC Verify has contacted OCF to request access to previous inspection documents.

Authorities say they will also focus on exit routes to the bar, which spans two levels: a ground floor and a basement. The fire apparently started in the basement, where the two images mentioned above were taken.

Videos filmed at the time the fire broke out show people trying to put out the flames before attempting to exit the basement via a narrow staircase.

Professor Galea said stair exits can be deadly bottlenecks, with people tripping and being trampled.

He added that even if there were other escape routes, panicked people in unfamiliar spaces would be more likely to exit the same way they entered.

Officials also confirmed that there was more than one exit from the building, but added that they were “unable to say at this time” whether the emergency exit was open or closed at the time.

“There is not just one door, even if at the time of the fire, it seems that most people went out through the main entrance. But this building is a public place. It was obviously equipped with an emergency exit,” declared Valais State Councilor Stéphane Ganzer.

Pilloud told reporters that the bar’s two French managers had been questioned as well as people who escaped the fire.

One of the bar’s owners reportedly told local media that the establishment had been inspected three times in the past ten years and that everything had been done according to regulations.

Investigators say they also analyzed other videos from the scene.

A video we found shows sparklers attached to bottles being used inside the bar as early as 2024.

It shows women dressed in distinctive protective helmets carrying the bottles and pyrotechnics to customers, before untying them and serving drinks.

The footage was uploaded to YouTube in May 2024 by the account @ConstellationCransMontana, although we cannot know for sure when it was filmed.