A flashover likely occurred during the Swiss nightclub fire. Here’s what that means
Soaring temperatures in enclosed-space fires mean the entire contents of a room can ignite almost simultaneously, with unsurvivable consequences for those inside.
A flashover likely occurred during the Swiss nightclub fire. Here’s what that means
By John Yoon
January 3, 2026 — 1.30pm
The cause of the fire that left dozens dead at a bar in Switzerland in the early hours of Thursday is still under investigation. But Swiss authorities have said it’s likely that the explosion reported from the site was caused by a flashover.
A flashover is a common and deadly phenomenon in which a fire in an enclosed space rapidly spreads, igniting nearly everything in the room almost simultaneously, according to fire experts.
Social media footage showed the early stages of the fire as it spread across the ceiling.Credit: X
Authorities said this probably happened at Le Constellation, the bar in the ski resort town of Crans-Montana, where flames ripped through the building, causing at least one explosion and killing about 40 people.
Béatrice Pilloud, the local attorney-general, said at a news conference on Friday that initial evidence suggested that the fire started from sparklers attached to bottles of champagne that were held too close to the ceiling.
When a flame in a room is not quickly put out, hot gases rise to the ceiling and spread heat throughout the space, fire experts say. Temperatures can rise quickly to as high as 1000 degrees, a point at which everything in the room can start burning at once, according to the US National Fire Protection Association.
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“All the wood, all the seats, all of the decorations and everything else in the room would be heated to the ignition temperature,” said Steve Kerber, executive director of the Fire Safety Research Institute in Maryland. “If you have very combustible materials, like plastics, it happens very fast.”
In a flashover, a flame can spread from a candle to a sofa, then to the carpet and the rest of the room in three to five minutes, depending on the types of materials involved, Kerber said.
It would burn the people inside, too.
Even a firefighter in full protective gear would be unlikely to survive a flashover, according to the National Fire Protection Association.
