Wildifre papers
Why some homes survived: Learning from the Fort McMurray wildland/urban interface fire disaster
By Alan Westhaver, M.Sc.
March 2017
ISBN: 978-1-927929-04-9
Abstract
In early May 2016 Fort McMurray, Alberta (population ~90,000) experienced the largest in a series of increasingly disastrous wildland/urban interface fires to recently occur in Western Canada. More than 2,400 structures were destroyed, insured losses approached $4 billion, and untold hardships now lay ahead for thousands of citizens of Fort McMurray who suffered displacement and disruption.
When the damage extent became apparent, the Institute for Catastrophic Loss Reduction sought permission for on-site access and tasked the author with conducting an investigation to answer the vital question: ‘Why did some homes survive this wildland/urban interface fire with little or no damage, while others were vulnerable to ignition and destroyed?’ A methodology to evaluate the relative vulnerability or fire-resistance of homes was developed. Observations concentrated on homes near the edge of urban neighbourhoods where wildland fire first spread to, and established among, structures. Levels of hazard associated with 20 individual factors contributing to ignition potential of homes were evaluated. Sampling also occurred in country residential areas. Field investigations took place May 19 – 28, 2016.
The Fort McMurray wildland/urban interface fire disaster provided an unprecedented opportunity to learn firsthand about the survival and ignition of homes. Results of field evidence combined with observations regarding the arrangement of homes, forest fuels, and clearances between them led to the conclusion that the vast majority of initial home ignitions within this transition zone were most likely caused by embers of the forest fire. Based on sites visited, no instances were observed where home ignition could confidently be attributed to direct contact by flames of the burning forest, and there were very few observations where home ignition was likely due only to radiant heat from the forest.
Overall, observations made during this investigation confirm that the Fort McMurray disaster followed a well-recognized pattern known as the ‘wildland/urban interface disaster sequence’. This progression can only be broken, and disaster avoided, by substantially increasing the proportion of homes that are resistant to ignition – especially by embers. Some encouraging evidence in support of halting the ‘disaster sequence’ was found at localized sites on the urban perimeter, but these were not numerous enough to deter the spread of fire from structure to structure towards the urban core, and eventual development of an urban conflagration. In these regards, the results of this investigation closely align with those from similar case studies and research conducted elsewhere.
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