Paris Soir - Soundproofing foam in focus in probe of deadly Swiss bar fire

The question of whether safety standards were respected has been debated since the fire broke out at Le Constellation bar in Switzerland's glitzy resort town Crans-Montana at around 1:30 am (0030 GMT) on Thursday, as the venue was crammed with young partygoers.

Beatrice Pilloud, the lead prosecutor in Switzerland's southwestern Wallis canton, told reporters Friday that the leading hypothesis was that "sparklers or Bengal candles attached to champagne bottles and lifted too close to the ceiling" of the bar's basement had ignited the deadly blaze.

One video shared on social media showed the low ceiling -- covered with soundproofing foam -- catching alight and the flames spreading quickly, as revellers continued to dance, unaware of the death trap they were in.

Once they realised, panic set in.

"The investigation is indeed focusing on the installation of this foam", and it will have to determine whether this soundproofing material "is compliant" and whether it "caused the fire or not", Pilloud said.

- 'Very easily flammable' -

For Freddy Rigaux, a former professional firefighter in France and a court-appointed expert, the material visible in videos shared online corresponds to products that are "easily, even very easily, flammable".

It clearly did not meet the so-called M1 fire-resistance standards required for ceilings in public buildings in France, he said, explaining that M1-rated materials are combustible, but not flammable.

"They will degrade under the effect of heat, but will not produce flames, particularly flaming droplets as seen in the video," he said.

When soundproofing foam is not treated with flame retardants, fire can spread very rapidly, the expert explained.

- 'Inconceivable' -

According to Romain Amisse, another court-appointed fire expert, the fumes emitted when such material burns are toxic, especially in very confined spaces, as is the case in the Le Constellation's packed basement.

He said the Swiss tragedy was reminiscent of the Cuba Libre bar fire, which killed 14 people in Rouen, northern France, in 2016.

In Crans-Montana, "you have pretty much the same situation, with highly flammable foam on the ceiling that produces a lot of smoke", he said.

David Zenouda, the vice-president of the Union of Trades and Industries in the Hotel and Catering Sector in Paris, said using the type of foam seen in the Crans-Montana images for soundproofing a venue was "inconceivable".

"For soundproofing, we have specific materials for covering ceilings and walls, creating a kind of box within a box," he told AFP.

What you want, he said, was to create a "box with a plasterboard panel... on which you place tar paper panels with rock wool, and then another panel".

"It is very complex and requires significant investment," he acknowledged.

By contrast, he said, the method that appears to have been used at the Le Constellation bar is equivalent to "soundproofing material for media booths or recording studios", not for establishments open to the public.

The danger posed was "exactly the same" as if the bar managers had decided to cover their venue with nylon sheets, he said.

"Combined with the sparklers... the effects would have been the same."

U.Andre--PS