Investigators are racing to establish how and why the deadly New Year's Eve fire at a bar in a Swiss ski resort spread so rapidly. Authorities on Friday said in a press conference that sparklers attached to champagne bottles held too close to the ceiling appear to have started the blaze in the basement of Le Constellation bar in Crans-Montana.

But how the fire took hold with such ferocity, killing at least 40 people and leaving 119 injured, many seriously, is now a key focus for officials - as is the bar's safety record.

​​BBC Verify has been examining videos taken by survivors and onlookers and speaking to fire safety experts to find clues about what went wrong.

Bottles with sparklers held in the air

Two striking images shared widely online show people carrying champagne bottles with lit sparklers above their heads, with a crowd around them. One image shows flames starting to gather on the ceiling above people holding these bottles aloft.

The second image is a closer-up angle, showing a person wearing a crash helmet and holding a bottle with a lit sparkler, sitting on the shoulders of another person wearing a Guy Fawkes mask. The sparks from this bottle appear to be closer to the ceiling.

​​BBC Verify determined these images were taken after midnight on 1 January by confirming there were not earlier versions and matched them against public photos of Le Constellation - using details including the bar design and distinctive pipework.

In other videos we verified from the night of the fire, some people can be seen filming the flames as loud club music thumps in the background. In one video, some people start to hurry for an exit stairwell while shouting.

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

Questions about foam padding on ceiling

Another focus is on foam-like padding on the bar's ceiling and whether it was compliant with safety standards.

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

PU foam is often treated with fire-retardant before being installed as a noise dampener in factories and entertainment venues; however, untreated foam can be highly flammable. Experts explained that, once ignited, polyurethane foam could lead to rapid flame spread, significantly reducing escape time for patrons.

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

Exit routes from the bar

The authorities say they will also focus on exit routes at the bar, which sits across two levels - a ground floor and a basement. Videos filmed as the fire took hold show people trying to extinguish the flames before trying to get out of the basement up a narrow set of stairs.

Officials also confirmed there was more than one exit from the building, but they were not currently able to say whether the emergency exit was open or closed at the time.

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

Sparklers used before

The investigators say they have also been analyzing other videos of the venue. One video shows sparklers attached to bottles being used inside the bar as far back as 2024.

It shows women dressed in distinctive crash helmets carrying the bottles and pyrotechnics to customers, before detaching them and pouring drinks.