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Embers, Wind, and Fire: A Dangerous Mix

Robert Ferrell
June 1, 2023

Wildfires can advance so rapidly that "spread like wildfire" has earned cliché status. But one of the key ways wildfires spread just might surprise you. Embers, also called firebrands, can act as wildfire super spreaders. Read on to better understand embers and explore specific tips you can share with your customers to help them protect their homes.

Embers are burning pieces of airborne wood and/or vegetation produced by wildfires, and they can travel miles in the wind, posing a major fire risk to structures in and around the wildland-urban interface (WUI).1 The Insurance Institute for Business & Home Safety (IBHS) calls ember storms the greatest danger to homes and businesses in the WUI.2 

How do embers contribute to wildfire risk?

Fire ignites when fuel, heat, and oxygen mix in the correct proportions. In wildfires, this fuel consists of not only natural materials like trees and brush but also man-made items like homes, landscaping, and fences.

Firebrands originating from wildfires can blow onto buildings in advance of approaching flames and even after the flames have passed. If these firebrands land on combustibles — such as mulch, leaves, firewood, or deck furniture — they may start a spot fire. In the right conditions, a spot fire can grow quickly and ultimately cause the loss of not only the structure where it started but also other structures.

Embers can also enter buildings through vents and windows, making these places especially vulnerable and important to protect. 

If embers enter a building or land in an attic, they can cause the structure to burn from the inside out.   

Home attic burning after an ember got insideEmbers can carry as far as a mile in the wind,
and when they get into an attic, they can start a fire.


Fire Safety Tips for Consumers


What makes embers so dangerous?

Embers can cause wildfires to spread not only quickly but also unpredictably. Embers can advance a wildfire forward on the wind, causing the fire to grow larger in size and scope. They can also cause a fire to re-ignite in areas its already passed, leaving embers behind which smolder and, under the right conditions, ignite. As a result, firefighting leaders can face major challenges when deciding where to place teams, and firefighting teams can have a difficult time determining which structures they should attempt to save.3

Fire scientists are also still learning about how embers spread and how they can be controlled. Michael Gollner, a fire scientist at the University of Maryland, demonstrated that a single ember, or even a handful of embers, can't generate much heat. But once you have even just a small pile of embers, they can produce the radiative heat necessary to ignite many materials, including wood.4

A key takeaway from Gollner's research is the importance of protecting structures from ember buildup, which is easier when you know the zones of vulnerability. 

Which areas around a home are most vulnerable to embers?

The National Fire Protection Association (NFPA) has identified zones of fire vulnerability around a home that matter most when it comes to controlling the spread of wildfire.5  

Perimeter map fire danger 2

Immediate zone: This includes the home and the area 0 to 5 feet from its furthest attached exterior point. This is the most important zone and the most vulnerable to embers.

Intermediate zone: This zone extends 5 to 30 feet from the furthest exterior point of the home and includes landscaping and hardscaping that can influence fire behavior.

Extended zone: This zone covers from 30 to 100 feet from the structure's furthest attached exterior point. It can include surrounding trees, sheds, play structures and accumulations of debris, all of which can fuel a fire and cause it to spread. 


Underwriting Property: A Guide to Fire, Wildfire and Earthquake Risk


How insurance professionals can help homeowners protect their property

The NFPA provides a variety of useful resources for homeowners that you, as a property insurance professional, can share with your customers. One resource is the Home Ignition Zone Checklist, which outlines steps homeowners can take to protect their houses from firebrands and to discourage fire from spreading.6 Items to consider in the Immediate zone include:

  • Clean roofs and gutters of dead leaves, debris, and pine needles that could catch embers.
  • Replace or repair any loose or missing roof tiles or shingles to prevent ember penetration.
  • Reduce embers that could pass through vents in the eaves by installing one-eighth-inch metal mesh screening. 
  • Clean debris from exterior attic vents and install one-eighth-inch metal mesh screening to reduce embers.
  • Repair or replace broken windows and damaged or loose window screens.
  • Screen or box-in areas below patios and decks with wire mesh to prevent debris and combustible materials from accumulating.
  • Move any flammable materials away from wall exteriors — mulch, flammable plants, leaves and needles, firewood piles — anything that can burn. 
  • Remove anything stored underneath decks or porches.

For more resources from the NFPA that you can share with customers, click here

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[1] National Geographic, https://www.nationalgeographic.com/science/article/meet-the-wildfire-superspreaders-embers

[2] Insurance Institute for Business & Home Safety, https://ibhs.org/wildfire/building-vulnerability-to-ember-exposure/

[3] National Geographic, https://www.nationalgeographic.com/science/article/meet-the-wildfire-superspreaders-embers

[4] Smithsonian Magazine, https://www.smithsonianmag.com/science-nature/untangling-physics-firenadoes-drifting-embers-other-wildfire-phenomena-180971735/

[5] National Fire Protection Association, https://www.nfpa.org/Public-Education/Fire-causes-and-risks/Wildfire/Preparing-homes-for-wildfire

[6] National Fire Protection Association, https://www.nfpa.org/Public-Education/Fire-causes-and-risks/Wildfire/Preparing-homes-for-wildfire 

Robert Ferrell, P.E. is WSRB’s Vice President of Public Protection. He leads the team that manages the insurance rating of cities, fire districts and building departments throughout Washington state. He has more than 25 years of experience in fire insurance rating.



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