The Crans-Montana fire bears the signature of flashover, the terrifying phenomenon by which a growing fire ignites much of a room nearby simultaneously. As America’s National Institute of Standards and Technology describes it, flashover occurs when a fire’s gases become so hot—exceeding 1,100 degrees Fahrenheit—that the intense heat ignites exposed surfaces almost at once, suddenly engulfing an entire space. In a low-ceiling basement lined with combustible finishes—as Le Constellation seems to have been—a small fire can rapidly generate a superheated smoke layer near the ceiling that gradually expands downward. Once that layer reaches critical temperature, the entire room can catch fire in seconds, turning a crowd-control problem into an inescapable inferno.