In 2020, a series of wildfires burned in Napa county CA. My mom lived just 25 miles away. She was worried. She had heard that embers can blow miles downwind from a fire and burn down houses.
Was she right to be worried?
Short answer: No. The Napa fires never came close enough for its embers to threaten her home.
Let’s take a look at when mom should worry.
It’s the embers that do it!
Mom was right that most homes that burn down in a wildfire are set on fire by embers falling on them and lighting the house.
“An ember is a small, glowing piece of superheated wood, coal or other material that remains after (or sometimes precedes) a fire. Embers can glow as hot as the fire from which they arise, and are light enough to be carried by the wind for long distances without being extinguished. They’re the primary reason properties go up in flames whenever a wildfire is nearby.”
Red White and Blue Fire says that 60% of homes burn from embers. That site also has a video that dramatically demonstrates that it is embers and not radiant heat that you should worry about.
So, Mom is right to be concerned about embers, but how far can they travel?
How far can embers travel?
Our short answer: Possibly as much as 5 miles, but probably less than 1 mile.
We base that answer by looking at many sources across the web, including these:
“These burning embers or firebrands can travel from one-quarter to one mile in the wind.”
“Flying embers can destroy homes up to 1 mile from wildland areas.”
“But embers can travel several miles ahead of the actual fire due to wind and intensity of the fire.”
“Flaming brands and embers can travel as far as five miles ahead of the active front of a wildfire.”
The most definitive answer we found is in Embers start spot fires: The real and the imagined stories, citing research published in the International Journal of Wildland Fire:
“In a study of 245 extinguished fires, experiments and simulations, and observing 48 wildfires, ‘The longest spotting distance was observed as 2.4 km.’”
The wide range of distances cited reflect that situational conditions play a large role, and whether the authors are trying to emphasize the most likely or the most extreme possibilities. If conditions are right (or wrong, so to speak), high winds and the right kind of material is burning, embers can travel far!
So, Mom needn’t have worried about embers from the fires in Napa. They never got close enough to threaten her house.
And then, when the fires are burning, she should monitor alerts from local authorities, even if she does live 25 miles away – fires can move fast.
Finally, of course, should the fire come closer, she should get out early if she felt at all threatened.