Glenn McGillivray is managing director of the Institute for Catastrophic Loss Reduction
After it was clear that the wildfire was not going to return to Fort McMurray, but before residents were allowed home, photos and video from media outlets showed numerous cases of seemingly untouched homes amid a sea of ash and debris.
The question that immediately arose among the researchers in natural hazard mitigation at our shop was, “why?” Why did some homes survive the inferno amid entire neighbourhoods almost completely razed by fire?
A researcher at the Institute for Catastrophic Loss Reduction has found the answer, and it’s all about the embers.
After evaluating the fire environment and clearances between homes and the forest edge, noted wildfire expert and consultant Alan Westhaver discounted direct contact from flames or radiant heat of the forest fire as being significant sources of home ignition at Fort McMurray. Instead, he concluded that wind-driven embers were the most probable cause for the majority of early home ignitions in the areas where the fire made its transition from forest into urban neighbourhoods.
“In all neighbourhoods studied, homes whose owners had adopted FireSmart [a program that provides information and tips to communities and property owners on how to prevent or limit the impact of wildfires] survived much more frequently than homes where FireSmart was not adopted,” Mr. Westhaver says.
Most people have the perception that a wildfire enters a built-up area like a bulldozer – a wall of flames that essentially engulfs anything and everything in its path. But our research (and that of others) indicates that this is not the case.
The fire one sees in the forest (usually while watching the evening news) is not the fire that enters town and causes havoc. There is a point where the former changes, from a fire that consumes almost nothing but vegetation to one that begins to feast on buildings and vehicles. And the transformative mechanism in this sequence is almost always airborne embers.
While in some cases, flames and heat from the wildfire can torch buildings immediately abutting the forest, this is rare. Instead, what tends to happen is that embers or firebrands (such as burning cones, bark fragments or branches) blow ahead – often way ahead – of the fire front and land on flammable material. In many cases, the embers burn out, causing no problems. But under the right conditions, they start spot fires on roofs, decks, dry lawns, mulch-lined flowerbeds or patio furniture, which can lead to the ignition of buildings. This can then give rise to the ignition of other, nearby structures through building-to-building spread of fire toward the urban core. Once this happens, an urban conflagration can occur, as it did in Fort McMurray.
The research conducted by ICLR in Fort McMurray and other research out of the U.S. and Australia is prompting new thinking in the area of wildfire mitigation.
The results of this work may eventually lead to less emphasis on thinning forests of excess fuel in wide swaths around communities and on construction of more and wider fire breaks (which do serve several purposes, but are ineffective against ember storms generated by intense fires of the kind seen at Fort McMurray) and also deflate any rationale for multiplying current fire-suppression resources.
Rather, the future of wildfire mitigation lies in breaking the wildland-urban interface disaster sequence. This will involve more engagement with communities, including homeowners, on the relatively simple and inexpensive – often cost-free – actions that can be taken to prevent embers from igniting homes and sparking large, urban fires. These actions can include not storing firewood, surplus building materials or petroleum products beside homes; not locating wood sheds or fences next to homes; keeping properties (including roofs and gutters) free of organic litter, such as leaves, pine needles and fallen branches; and landscaping (i.e. “firescaping”) using low-risk choices for plants, trees and shrubs, locating them away from structures, and avoiding the use of such items as wood mulch and bark chips.
Wildfire-risk reduction is beginning to move more toward a dialogue about what private property owners can and should do to protect the biggest asset they own, rather than what government and firefighters should do or have failed to do.
It’s largely about what’s happening – or not happening – right in people’s front and back yards.Report Typo/Error
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