Retracing flames’ destructive path

23 December 2007

SAlexander Maranghides, a fire engineer with theU.S. Commerce Department’s National Institute of Standards and Technology, stoodon a promontory overlooking the San Pasqual Valley, tracing the path the firetook into the woody, upscale Rancho Bernardo neighborhood called The Trails.

He and other fire scientists and officials are using the Witch fire as alearning opportunity.

On this day, he was studying how a wild land fire’s behavior becomes lesspredictable when it jumps from natural vegetation to the hodgepodge of fuels ina suburban neighborhood.

He pointed out the lines of trees along the river on the valley floor that thefire followed like a track.

“Witnesses said it looked like a train,” he said.

As it branched up side-canyons and slopes, it climbed to the houses with varyingintensities. Thick chaparral or trees produced more intense flames than adjacentareas of low grass. Indentations in the hillside focused flames like a torch,while bulges diffused them.

Wood decks, patio furniture, trash cans and fences served as steppingstones forthe fire to approach a home. Many, but not all, houses on the development’sperimeter were consumed.

Inside The Trails, the threat changed. Streets and driveways acted as firebreaks,hindering the fire’s advance along the ground. From that point on, he said, themain danger was embers.

Standing in front of a burned house inside the neighborhood, he cited evidencethat buttressed his observation: The property’s landscaping was green andhealthy. Clearly, it wasn’t the fire’s advance that had destroyed the home.

He pointed to the lawn, where embers had landed and petered out. He picked up acharred chunk about the size of a wallet.

“That is insulation,” he said, probably from homes burning across thestreet. He described a chain reaction in which houses closest to burningchaparral catch fire, then spew larger embers into the air that ignite housesfarther inside the development.

All told, about 70 of the community’s 240 houses burned.

While Maranghides studies why the homes burned as part of a long-term researchproject, Ernylee Chamlee, California’s chief of wildland fire preventionengineering, is looking for lessons firefighters can apply immediately.

One day, with Times reporters in tow, she visited areas of seemingly randomdestruction and provided likely explanations of how the fire progressed.

Two short cul-de-sacs, side by side with their backs to a canyon, weathered thefire very differently.

On Canfield Place, five of six homes burned to the ground. On Hadden Hall Court,which was set slightly farther back from the canyon’s edge, six of seven homessurvived without damage.

Chamlee’s on-the-spot analysis: Fire crested the canyon wall and burned a homeat the end of Canfield. That spread to two adjacent homes.

The worst threat in a neighborhood where homes are built close together is astructure burning next door, she said.

Not only does a burning home disgorge a vast number of high-intensity embersinto the air, but flames catch the eaves and fences of adjacent homes.

Heat cracks windows, exposing curtains and shutters to raw flame.

As the three homes on Canfield burned, she posited, they launched embers thatblew across the street and ignited two more.

The wind drove the embers over a one-story home on the adjacent cul-de-sac andignited a two-story house next door.

Firefighters helped prevent the fire from spreading to other houses on thestreet, including Rick Connolly’s next door.

Connolly had made a common mistake, leaving his garage door open when heevacuated. When he returned, he found embers had made it into the garage andtraveled through his laundry room and into the dining room.

Fortunately, his floor was tile. Nothing burned.

A couple of blocks away on Lancashire Way, where 29 homes burned and 26 survived,a home stands with burned-out lots on either side.

The fire cracked its windows and melted vinyl blinds but did not catch thehouse.

The likely key to the one-story home’s survival, according to Chamlee: a pair oftwo-story homes across the street that diverted the flow of embers over it andonto a street down the hill.

“Embers were just flying right over that house,” said Dennis French,who was on the street during the fire to help evacuate a friend. “It wasjust like a jet stream.”

24. November 2017/by GFMCadmin