Taking Houses Out of the Wildfire Equation

SEELEY LAKE – After three weeks of Sprague Fire burning around Glacier National Park, it reached the Sperry Chalet complex Aug. 31, 2017. In the final report issued by the National Park Service June 21, it was determined that despite the best efforts of firefighters to protect all the structures at Sperry Chalet, an ember entered the dormitory near a second story window and ignited the wooden portion of the structure.

In a press release, Secretary of the Interior Ryan Zinke applauded the firefighters efforts to save the chalet. "Still, the size and scope of the Sprague Fire reminds us that aggressive fuels management is necessary to keep Americans safe from wildfires, particularly in the West. We need to continue removing the dead and dying timber from our forests so that we can truly address this problem."

Retired research physical scientist Dr. Jack Cohen asked a different question in an attempt to change perspective at the Clearwater Partners Workshop June 21 in Seeley Lake.

"During the disaster conditions, we have no choice to do control. We tried and we failed," said Cohen. "We have multiple houses exposed, and we cannot, will not be there. Given that it's during the conditions when we cannot control the wildfire, how do we prevent wildland urban fire disasters? Does that mean that our homes are destined to be destroyed? I would resoundingly respond to that with NO, it's not."

Cohen has been interested in understanding the wildland-urban (WU) fire problem since the 1970s. He formally started his research on how structures ignite during wildfires in 1989. Through his research he developed the home ignition zone concept and has applied his understanding to developing the Firewise USA program.

"There's no way to keep wildfires from occurring. And wildfires are going to occur during extreme conditions, so extreme wildfires are going to be evitable as well," said Cohen. "Ironically we actually need more fire today, not less fire, to match the ecological realities of our landscape, but in different ecological conditions than what we primarily have occurring today."

When WU disaster occurs, it is during the two percent of wildfire that fails suppression burning under extreme conditions. Rapid fire spreads and high intensity fire contributes to significant firebranding and very high growth rates. High density of homes causes an urban conflagration problem.

"Wildfire can produce firebrands and lob them into about a quarter mile into the community simultaneously. Fire suppression is completely overwhelmed. That means that 80-95 percent of the houses have NOBODY THERE," said Cohen.

When firefighters are not present, all it takes is one sustained ignition on a house – from firebrands landing in receptive fuel in contact with the structure or surface fire reaching the structure – for it to burn.

"So although initiated by intense wildfire, it's the firebrands from a surface fire that typically ignite a home. I'm telling you that it's the house itself that met those conditions for ignition, not the big flames of anything around – just the firebrands," said Cohen.

Through his 20-year journey researching the characteristics of home ignition, Cohen found if the local conditions within 100 feet of a structure do not meet the requirement for local combustion, it will not ignite during an extreme wildfire event.

Through extensive experiments, Cohen found that to ignite a wood wall in a crown fire from thermal radiation, it has to be within 100 feet. Cohen said this is hard to believe because of our human perception of fire.

"My skin is highly sensitive...a fire exposure that causes me discomfort in five seconds takes 27 minutes to ignite wood," said Cohen. "[During an ember shower] you can stand there because there is no thermal exposure."

However, when a crown fire hits a fuel break, such as a street, natural barrier or treatment area, the fire stalls.

"A fuel break really protects a fuel break, but it doesn't stop the fire – why – because of burning embers. Flames don't leap over long distances, firebrands do," said Cohen.

Firebrands that cause home ignitions commonly travel more than a half mile depending on the type of vegetation. Once structures and vegetation within a development ignite, they become a significant source of firebrands.

Cohen said the two factors that make homes the most vulnerable are wood roofs and spot fires. While a combustible roof is self-explanatory, homes with a roof covered in composite shingles or metal with concentrations of pine needles can be problematic if the needles burn long enough to ignite the eaves, walls or roof.

Spot fires started by firebrands landing in receptive fuel beds including the needles or pine scales that have accumulated on or under the deck, a broom leaning against the wall outside, deck furniture cushions, firewood stacked next to the structure or in a bag of briquettes can cause the structure to ignite. Also, any fuel that holds flame in direct contact with the structure can also cause total destruction.

Cohen emphasized that the homeowner is the only one with the authority and responsibility to modify the local conditions and reduce the vulnerability of homes to wildfire. Without their engagement, he said responding fire protection will not be effective.

"So understanding how homes ignite during extreme wildfire shows us how local ignition conditions determine home ignition," said Cohen. "By eliminating ignition vulnerabilities within the home ignition zone, you can prevent home destruction and wildland urban home disasters."

Many of the videos of Cohen's research are available on YouTube. Search for "Jack Cohen Home Ignition."

Also, Clearwater Resources Council still has grant funding to cost share up to 50 percent for fuel mitigation on private property. Homeowners can also request a free home inspection through CRC by contacting Community Forester Signe Leirfallom, 546-4467 or email signe@crcmt.org.