Image of forest fire buring at night

Bobbie Scopa worked the Yellowstone fire of 1988. The smoke was so thick that it had created its own weather—an inversion that locked the forest into a dense cloud of soot. “In the middle of the day we had to have our headlamps on just to read our maps,” she recalled years later. Visibility was down to 30 or 40 feet and the fire itself was hidden. All she had to go on was the sound.

There would be dead calm as the fire choked on its own smoke at times, and then it would come to life with fresh oxygen. Scopa, now a Deputy Regional Fire Director with the Bureau of Land Management, told me the story several years ago, and this summer’s intense fire season prompted me to revisit our conversation. She had talked vividly about what she heard on that day.

“The fire was on the hill above us,” she recalled, “and about every 30 minutes we would hear a roaring sound where that fire would get enough air and make a run. And that sound is something that will always stick with me. I’d been around some blowups before, but that was probably the most intense one that I’d heard up until that time.”

When fire fighters talk about “blowups”—a sudden rush of flames and thermal wind as a wildfire explodes—they often talk about the sound.

Perhaps the most famous description comes from Norman Maclean in his book “Young Men and Fire”, in which he describes his own encounter as a firefighter in Montana in 1949. “Behind where I did not dare to look, the main fire was sound and heat, a ground noise like a freight train.” Maclean refers to the noisiest machine of the 1940s, but Scopa updated it a little.

“It sounds kind of like a jet engine at the airport when you’re sitting there and the jet throttles up. Well, imagine if that jet throttles up but it’s fastened hard to the tarmac at the airport. It’s just a roaring sound.”

Scopa has since heard the sound at other fires and she said it is easy to recognize and always a signal to retreat. “If you heard that sound,” she said, “even if you didn’t know what that sound was, you’d know that this is either the end of the world or there must be some major fire activity going on.”

Not all fires turn into blowups. The conditions have to be just right. Wind, dryness and topography all conspire to create literal tornadoes of fire that roar like gigantic blowtorches. They are one of the chief dangers of fighting forest fires, and they can easily outrun a human. Maclean dedicates most of “Young Men and Fire” to understanding the blowup that killed 12 smoke jumpers in the Mason Gulch Fire of 1949.

I’ve been searching all over for a recording of the sound of a blowup, but so far have had no luck. The typical answer I get when I ask around is that anyone who has ever heard it was probably running too fast to bother to turn on a tape recorder.

“If you’re not too close, it’s pretty awesome to watch,” recalled Scopa. “It’s like watching a tornado or some other force of nature at work. It’s pretty cool to watch it until it gets close and you realize it’s coming your way.”