While the cause of the Los Angeles area fires remains undetermined, the spread of flames is clearly linked to embers.
The fires, which began last Tuesday, have sadly resulted in fatalities and destroyed over 12,000 structures. Strong winds have exacerbated the fires, increasing oxygen supply and carrying embers to unburned areas.
Contrary to common assumptions, experts explain that most wildfire-related home destructions are caused not by direct flame engulfment, but by ignition from airborne embers.
Let’s examine what embers are and their role in wildfire propagation.
What is an ember?
An ember is a piece of burning debris; once airborne, it’s technically termed a firebrand, explains James Urban, an assistant professor of Fire Protection Engineering at Worcester Polytechnic Institute.
“In wildland fires, these are typically burning pieces of wood or vegetation,” he states. “However, in urban fires, they can be vegetation, parts of houses, or virtually any combustible material.”
Their size varies, from tiny particles to larger fragments.
What are they capable of?
Anne Cope, chief engineer at the Insurance Institute for Business & Home Safety, highlights the significant difference between embers from a campfire and those involved in wildfires.
“These embers can travel for miles, often overwhelming neighborhoods near wildlands with a shower of embers,” she explains.
Wind intensifies ember combustion and energy release, making them potent ignition sources, Urban adds. These firebrands accumulate, often nesting in spaces like between fence slats or in shrubbery, starting new fires.
In 2017, embers crossed a six-lane highway in Northern California, igniting businesses and spreading rapidly from house to house in Santa Rosa.
“The prevailing belief was that embers wouldn’t travel that far across an interstate,” Cope recalls. “Clearly, that assumption proved dangerously wrong.”
While a ground ember might extinguish within minutes, it can also smolder, Urban notes. “Then, a sudden shift in conditions, like a wind gust, can reignite flames and cause widespread destruction,” he adds.
How are researchers studying embers?
Worcester Polytechnic Institute, collaborating with San José State University, is part of a Wildfire Interdisciplinary Research Center. With funding from the U.S. Forest Service and National Science Foundation, researchers investigate firebrand production and incorporate this knowledge into wildfire spread models and home defense strategies, Urban explains. For instance, his students have experimented on how vegetation management around buildings affects fire spread between structures.
“I am optimistic that the ongoing research will improve our preparedness for future fires,” he says. “We will see more such events, and changes are necessary to alter the outcomes.”
Cope concurs.
“We need to strategically incorporate wildfire ember preparedness in far more areas than we currently do,” she emphasizes.
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