JACKSON, Wyo. — What do the different fire danger ratings and restrictions actually mean? It’s all about math, said Evan Guzik.
Guzik is the public affairs specialist for Bridger-Teton National Forest and Teton Interagency Fire crewmember. Fire danger is a careful calculation, he said.
“There’s no social component; it’s strictly based on factual data on the ground.”
To determine fire danger — that is, the rankings you see on signs in town and at trailheads that go from “low” to “extreme” — fire crews look at two things: reports from seven Remote Automated Weather Stations (RAWS) scattered in the forest, and fuel moisture. The former gives a snapshot of recent weather: rain, heat, wind, etc. The latter is a little more complicated.
A fuel source is what it sounds like: anything that could burn. But different fuel types have different burn potentials, measured in time it would take moisture to saturate. Grass is going to get pretty wet if it rains, Guzik explained. That’s considered a “one-hour fuel.” Big logs and downed trees, on the other hand, are going to take more time to dampen. They might be considered “10-hour” fuels, “100-hour” fuels, or even 1,000-hour fuels. In order to measure fuel moisture, the Forest Service collects samples of each fuel size and weighs them when they’re wet, then puts them in an oven to remove all the moisture and weigh them dry, Guzik explained. This happens, on average, every two weeks.
Still following? Great. This is where it gets complicated, but we’ll spare you the math. Basically, Guzik said, fire crews do a bunch of calculations to determine fuel moisture. They use those numbers, combined with weather reports from the RAWS, and come up with one final number: an Energy Release Component (ERC). That’s what they use to determine fire danger.
The Forest Service carries seasonal charts that map seasonal ERCs with historical averages, Guzik explained.
Fire danger is a “snap shot” of one moment, Guzik said. It’s all numbers. Fire restrictions take into account some more imprecise factors — what the weather might do, how this summer’s numbers compare to historic averages, local and national staffing available to respond to potential local fires. Above all, there’s the human factor.
“We look at things like how many fire starts we’ve had, how many abandoned campfires, visitor use numbers,” Guzik said.
It’s easy to think a couple of days of rain make for safer fire conditions. But it’s more complicated than that.
The stakes are too high to disregard fire danger and fire restrictions. Guzik calls it “values at risk.”
“In Teton County, you have million-dollar homes that are values at risk,” he said. “But you also have immaculate and wonderful viewsheds that people are drawn to and hold a really powerful emotional feeling with, and that is a value at risk at well.”
Editor’s note: This article was originally published on July 12, 2021, by Reporter Shannon Sollitt, under the title, “The science behind fire danger ratings and regulations.”
