Retracing flames’ destructive path

Alexander Maranghides, a fire engineer with the U.S. Commerce Department’s National Institute of Standards and Technology, stood on a promontory overlooking the San Pasqual Valley, tracing the path the fire took into the woody, upscale Rancho Bernardo neighborhood called The Trails.

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

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

He pointed out the lines of trees along the river on the valley floor that the fire 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 varying intensities. Thick chaparral or trees produced more intense flames than adjacent areas 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 for the fire to approach a home. Many, but not all, houses on the development’s perimeter 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, the main danger was embers.

Standing in front of a burned house inside the neighborhood, he cited evidence that buttressed his observation: The property’s landscaping was green and healthy. 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 a charred chunk about the size of a wallet.

“That is insulation,” he said, probably from homes burning across the street. He described a chain reaction in which houses closest to burning chaparral catch fire, then spew larger embers into the air that ignite houses farther 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 research project, Ernylee Chamlee, California’s chief of wildland fire prevention engineering, is looking for lessons firefighters can apply immediately.

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

Two short cul-de-sacs, side by side with their backs to a canyon, weathered the fire 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 homes survived without damage.

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

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

Not only does a burning home disgorge a vast number of high-intensity embers into 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 that blew across the street and ignited two more.

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

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

Connolly had made a common mistake, leaving his garage door open when he evacuated. When he returned, he found embers had made it into the garage and traveled 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 the house.

The likely key to the one-story home’s survival, according to Chamlee: a pair of two-story homes across the street that diverted the flow of embers over it and onto 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 was just like a jet stream.”