- The Washington Times - Friday, September 4, 2009

LOS ANGELES (AP) | A streak of soot on a rock. Singed bark on a tree. Charred plants and grasses.

Even in a landscape blackened by wildfire, clues abound for investigators following the path of a blaze back to its point of origin and trying to find out how it started.

In the hills above Los Angeles, a team of U.S. Forest Service investigators is undertaking that hunt as they work to learn what, or who, sparked one of the largest wildfires in Southern California history.

The blaze has claimed the lives of two firefighters, ravaged more than 250 square miles, destroyed more than 60 homes and continues to chew through a forest normally enjoyed by Los Angeles residents escaping the sweltering city.

The U.S. Forest Service said Thursday that the wildfire had been caused by arson and the Los Angeles County Sheriff’s Department launched a homicide probe looking for the person or people responsible.

Jeff Tunnell, a wildfire investigator for the Bureau of Land Management, said even in charred terrain, investigators can detect important signs in the soot.

“Fire creates evidence as well as destroys it,” he said. “We can follow fire progression back to the point at which it started.”

The key for investigators is to pinpoint that origin as fast as possible. They start at the place firefighters were first called, then interview witnesses and look for indicators on the ground to work backward to the fire’s place of ignition.

“You just follow your burn patterns,” said Mr. Tunnell, a veteran of 50 wildfires who is based in Ukiah in Northern California. Clues can come from burned trees and grasses, where the amount of burned foliage tells investigators the direction and speed a fire was moving.

Once they find the general origin of the fire, investigators set up a perimeter and search the area in a grid formation until they find the actual place of ignition, Mr. Tunnell said.

If investigators are lucky, the point of origin will not have been disturbed by firefighting. Sometimes efforts to douse the flames inadvertently destroy potential evidence with water or the machinery used to cut fire lines.

It is not known whether that is the case in this fire. A trio of Forest Service investigators wearing black gloves spent most of Wednesday scouring the area around a partially burned oak tree along a highway.

One investigator shook soil into a can, others used binoculars to examine the ground more closely. They planted red, blue and yellow flags along a burned-out rocky slope that climbed about 40 feet above the road. About 30 yards away, a smaller area was cordoned off with tape and orange cones.

“We look for something that is not supposed to be there,” said Forest Service spokesman Nathan Judy. “Something out of the ordinary - is there a cigarette there? A party spot, debris, kids out there with fireworks?”

At the point of origin, investigators are often able to find the remains of whatever started the fire: a charred match or cigarette butt, a piece of metal from a car, a piece of power cable. If no such object is found, investigators will often rule a fire to have been “hot set,” meaning it was started by a person holding a lighter to the brush.

“That’s what you are going to assume, because there’s no other competent ignition source,” Mr. Tunnell said.

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