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

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

Officials said at a press conference on Friday: sparklers attached to champagne bottles A fire held “very close to the ceiling” appears to have started the fire in the basement of Le Constellation bar in Crans-Montana.

But how the fire spread so violently, killing at least 40 people and injuring 119, many seriously, is now a key focus for authorities, as is the bar’s safety record.

​BBC Verify examines videos shot by survivors and onlookers and speaks to fire safety experts to find clues as to what went wrong.

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

In one photo, flames begin to gather on the ceiling of people holding five of these bottles aloft.

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

The sparks from this bottle appear to be closer to the ceiling.

Confirming the absence of earlier versions, BBC Verify determined that these images were taken after midnight on 1 January and matched them with publicly available photographs of Le Constellation using details such as the bar design and distinctive plumbing.

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

In other videos we have confirmed from the night of the fire, some people in the bar can be seen filming the flames while loud club music can be heard in the background. In one video, some people start screaming and running towards the exit staircase.

Béatrice Pilloud, chief prosecutor for the Valais region, said Friday that everything led investigators to believe that the fire was caused by sparklers attached to champagne bottles that were “moved very close to the ceiling.”

Another focus is the foam-like padding on the bar’s ceiling and whether it complies with safety standards.

Two fire safety experts told BBC Verify that the materials seen in photos and videos of Le Constellation included “egg box foam”, a type of sound-absorbing material made from polyurethane (PU).

In the photo where the bottles are lifted into the air, flames can be seen on the part of the ceiling covered with a foam-like coating.

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

However, it can be extremely flammable if left untreated.

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

Professor Edwin Galea from the University of Greenwich said the effectiveness of retardant treatment on PU foam may decrease over time.

Swiss authorities said they could not confirm what type of foam padding was used in the bar and whether it met safety standards.

At Friday’s press conferenceAuthorities said there was a “flash” at the bar.

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

According to Michael Klippel, a fire safety expert at ETH Zurich University, “the probability of survival after the flash is very low.”

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

At a press conference, Swiss officials said that inspections should be carried out every year in a building the size of Le Constellation.

BBC Verify contacted OCF to request access to previous audit documents.

Officials say they will also focus on exit routes from the bar, which spans two floors, the ground floor and the basement. It is thought that the fire started in the basement where the two images mentioned above were shot.

Videos taken as the fire grew showed people trying to extinguish the flames before trying to escape from the basement via a narrow staircase.

Prof Galea said stairways could be deadly bottlenecks that could cause people to trip and be crushed.

Even if there are other fire exits, panicked people in unfamiliar areas are more likely to leave the way they came, he said.

Officials also confirmed there were multiple exits from the building, but added that they “cannot tell at this time” whether the emergency exit was open or closed at the time.

Valais state councilor Stéphane Ganzer said: “There is not a single door, despite the fact that most people left the main entrance during the fire. But this building is a public place. It was clearly equipped with an emergency exit.”

Pilloud told reporters that the bar’s two French managers were interviewed, as well as people who survived the fire.

One of the bar’s owners reportedly told local media that the bar had been inspected three times in the last decade and that everything was done according to the rules.

Investigators say they are analyzing other videos of the location as well.

In a video we found, it can be seen that sparklers attached to bottles have been used inside the bar since 2024.

The photo shows women wearing distinctive helmets removing bottles and pyrotechnics and carrying them to customers before pouring the drinks.

The footage was uploaded to YouTube by the account @ConstellationCransMontana in May 2024, but we can’t be sure when it was taken.