What Caused the LA Wildfires? How Investigators Will Find Out

How Will Fire Investigators Trace the Source of the L.A. Wildfires?

By Stephanie Pappas edited by Jeanna Bryner

As firefighters continue to battle the blazes that have destroyed thousands of structures in the Los Angeles area, fire investigators are already trying to figure out how the conflagrations began.

Local news agencies report that investigators are closing off streets at the possible ignition sites in the Palisades Highlands, the area of Los Angeles where the Palisades Fire, the largest of the fires in the region, began. The investigation is in the early stages, but officials may be able to find the cause, as they have in other wildfires. Fires can begin in any number of ways: naturally, with a lightning strike or, more often, through some human-related means—such as sparks from a downed powerline, a discarded cigarette butt, a poorly doused campfire or even arson. Between 1992 and 2012, 84 percent of all U.S. wildfires were human-caused.

Because there were no lightning storms in the L.A. area when the fire started, investigators will be looking for human-related causes. An early point of interest centers around Skull Rock, a landmark near a popular hiking trail above the Palisades Highlands, according to reporters who spotted crime scene tape, police and closed roads near the trailhead. The spot was the site of a small fire on New Year’s Day that was quickly put out. It’s possible for fires to leave embers that can be reignited by wind, but there are also power lines and a lot of human traffic at Skull Rock, leaving multiple possibilities open. [See Photos of the Los Angeles Fires]

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Meanwhile the investigation into the Eaton Fire, the second-largest blaze in the recent fires in the L.A. area, is currently focused on electrical transmission equipment in Eaton Canyon, according to the Los Angeles Times.

Bob Duval is a fire investigator and a regional director at the National Fire Protection Association (NFPA), an international nonprofit organization that puts out a document called NFPA 921: Guide for Fire and Explosion Investigations. It’s the closest thing to a Bible that fire investigators have, with instructions for how to seek out the cause of everything from a house fire to a blaze ripping across miles of forest. Duval spoke to Scientific American about how to investigate fires like those that have devasted the Los Angeles area.

[An edited transcript of the interview follows.]

How would an investigation like those now happening in the L.A. region typically start?

If it’s in an area that was populated, you may have eyewitness accounts of a driver who saw some flames or smoke alongside the road. You may have surveillance cameras or traffic cameras on highways. You’ve got pilots, commercial aircraft. Can you pin it down to an area based on eyewitness accounts or evidence like a power grid that suddenly shows a fault? If it’s thousands of acres, can I narrow it down to 10 or 15 acres on the side of this mountain or street and then take it from there? You have to be systematic.

And then there will be folks going into the field. You look at patterns. What direction did the fire come from? You look at a large tree. What side of the tree was burned? Does the burn pattern go upward or downward? Take a look at the canopy, the pine needles or leaves. What does it show about the direction of the fire? Then you’re going to look at the topography: The wind on one side of a hill is different than the wind on the other side. You have canyons, you have roadways that all impact the way the fire is going to spread.

With all that evidence compiled systematically, you’re reversing your way back into where the fire started. And then you start looking for causes within that area.

You think about a fire destroying everything, but it sounds like some evidence can be left behind.

That’s a common misconception, that with a fire investigation, everything is destroyed. That’s why people are under the misunderstanding that if they commit a crime, they [can] try to cover it up by setting the building on fire. Yeah, that may hide some evidence, but it also creates a lot of evidence.

For a campfire [that burned out of control], for example, you’re looking for: Did they stack wood or brush or twigs? Did they ball up paper? Did they put stones around it to contain it? You’d look for whether the ground is stamped down like there were people there for a while.

Is this a common trail used by motorbikes or ATVs [all-terrain vehicles] Is there any evidence of smoking? Was someone clearing brush? Was there anybody doing target shooting or hunting, where a spark or a hot shell from a firearm could have caused [the fire] Does anybody report hearing or seeing fireworks in the area?

Another potential cause is arson. That can be a little more difficult. If it’s a lighter, someone might put it back in their pocket and walk out of the woods. The fire may go undetermined, which is the official term used when we have an area of origin but can’t find a cause.

Are there differences between investigating wildfires, such as the L.A. fires, and fires that begin in a building?

Yes and no. Both of those arenas create patterns, and the investigator uses patterns to help determine the area of origin. In a building, it’s several compartments if you think of a home or condo. But in a wildfire, there are no compartments. It’s wide open. There’s unlimited air. Wind can play a role in a building fire. But in the wildland, wind is a major factor because it drives everything you do. There have been a lot of fatalities in wildland firefighting because the wind pushes the fire and overcomes the firefighters.

How long does an investigation typically take?

It could be months. I think the folks in California really have their work cut out for them. There are various reviews that the report has to go through. They’re going to want to make sure that everything is done as well as it possibly can be done. [That’s not to say that the process] should be any different if it’s a $10 fire or a $100 million fire. The investigation should still be done systematically and by the book. But you can imagine the scrutiny these reports are going to be under because there is potential for civil damage here.