A major wildfire has been advancing through the foothills near Los Angeles this week. By Wednesday, the blaze had consumed 140,000 acres and caused the state to spend more than half of its firefighting budget.
Investigators have concluded that the Station fire in Northwest Los Angeles was " caused by someone intending to set a fire," although they have not revealed any details about the evidence. How do you examine a wildfire for signs of arson?
First, figure out where it started. The place where firefighters first engaged with the blaze is a good place to begin, as are spots where eyewitnesses say they first saw flames or charred ground. Once there, investigators can lay down something like an archaeological grid and start sifting through the debris. This evidence might include the "puddle" burn patterns caused by an accelerant—or the remains of a cigarette. Investigators also look for footprints or tire marks, and they sometimes use magnets to find stray bits of metal that might have been part of a time-delayed incendiary device. (Read more on how investigators look for signs of arson.
Among the fires now classified as "active incidents" in California, the biggest is the Station fire. Others include the Oak Glen fire, the Big Meadow fire, the Black fire, and the Red Rock fire. Who picks these names?
In general, naming rights go to the group that makes the "initial attack" on a fire, whether it's a squadron of local firefighters or a team from the U.S. Forest Service. (In contrast, every tropical storm in the Atlantic gets its name from a single organization.) The commander on the scene often uses a nearby geographical feature to describe the fire, but he's not bound by any official rules. (Read more on how a wildfire gets its name.)
Gov. Arnold Schwarzenegger announced on Wednesday morning that the Station fire in Angeles National Forest had been 22 percent contained. What does it mean to contain a fire, and how is the percentage calculated?
To prevent a blaze from spreading, firefighters dig a "fire line" around its circumference. If three miles of fire line have been built around a fire that is 10 miles in circumference, then 30 percent of the fire is contained. Once a fire is fully contained, firefighters work on "controlling" it by battling it inside the containment line. A controlled fire is one that has no risk of expanding beyond the fire line. (Read more on how wildfires are rated.)
Reporters have described "billows of white and black smoke" in the Los Angeles area, along with a "brownish mushroom cloud … and a gauze of gray smoke." What determines the color of the smoke?
The type of fuel and how hot it's burning. A wildfire can produce both colors of smoke. First, the hot, flaming combustion of dry underbrush releases little particles of black soot into the atmosphere. But the blaze also produces smoldering combustion—think of the glowing logs at the bottom of a campfire—which don't burn quite as hot. Big branches or tree trunks that have a lot of moisture are more likely to smolder and release white smoke. (Read more on what determines smoke color.)
A pair of firefighters perished Sunday while trying to protect the crew of prison inmates that was assisting them. Why are prison inmates fighting fires?