What caused the LA fires? We explain what's known so far and how fire causes are determined

Investigations are underway into the causes of the Eaton and Palisades fires — two of the most deadly wildfires in state history. But how, exactly, do people determine what caused a wildfire? LAist spoke with two veteran wildfire investigators to find out.

What's known about the potential causes of the Palisades and Eaton fires

Many media outlets have reported that investigators are looking into whether the Palisades Fire may be a re-kindling of an earlier fire caused by fireworks on New Years Eve.

Meanwhile, investigators are studying an electrical transmission line in the Eaton Canyon area as a possible source of the Eaton Fire, according to the L.A. Times. The utility Southern California Edison denies its lines are responsible and says it has not been officially accused of causing the fire. Multiple lawsuits have already been filed against the company.

But what, specifically, happens when investigators try to determine the cause of fires?

Finding the point of origin

Investigators begin by focusing where the wildfire started, a technical, tedious task that can take hours or days, said Ed Nordskog, a retired arson/bomb investigator from the L.A. County Sheriff’s Department.

To find the ignition point, investigators trace the spread of a fire backwards, which is easier in wind-driven wildfires like the Eaton and Palisades fires than in a fire that broke out on a calm, windless day.

“If there's high winds, the wind takes the fire away from the origin. And it leaves a big, black finger of burnt ground pointing backwards upwind. And if you follow that, you’ll get to the origin,” Nordskog said.

A resident attempts to protect his property from the flames closing in on homes threatened by the wind-driven Palisades Fire in Pacific Palisades on Jan. 7, 2025.

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David Swanson

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AFP via Getty Images

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Determining cause

Next, investigators use flags and tape to create a grid around the origin, and methodically go through each square with magnifying glasses, magnets and binoculars looking for clues. Tiny molten metal particles may suggest that power lines slapped together in high winds, for example (this was the cause of the 2017 Thomas Fire in Ventura and Santa Barbara counties). A homeless encampment may suggest a cooking fire that got out of control.

“It'll take multiple people literally on their hands and knees looking at things smaller than your fingernail on the ground to see what could have caused the fire,” Nordskog said.

Investigators also track down video evidence and eye witnesses.

 ”You're canvassing neighborhoods and talking to maybe up to a hundred people who may have witnessed where it started,” said longtime fire investigator Tom Pierce, the owner of Piece Fire Investigations.

It’s important to stay neutral and ignore rumors circulating on social media and news reports about what may have caused the fires.

“Expectation bias is the worst thing to have in a fire investigator’s tool chest,” Pierce said.

Assigning responsibility

Once investigators have determined origin and cause, they begin the even more arduous process of figuring out who is responsible.

In this stage, investigators may subpoena records from utility companies, interview employees and search people’s phones. If a power line is the suspected cause, they may even remove the power lines in question and have electrical engineers examine them.

This process can take months or even years, Nordskog said, and can turn into a criminal investigation.

In California, there are two types of criminal fires: arson and reckless burning. Arson is always a felony, whereas prosecutors may charge reckless burning as either a misdemeanor or a felony depending on how bad the fire was.

Humans started over 4,000 wildfires in Southern California in 2023 alone.

Finally, lawsuits will almost certainly follow the investigations, as insurers try to recoup the cost of claims for thousands of damaged homes and victims seek compensation.

A home burns during the Eaton fire in the Altadena area of Los Angeles County on Jan. 8, 2025.

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Josh Edelson

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AFP via Getty Images

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“ You have to understand how much money's at stake,” Nordskog said. “I always say this: Fire is money.”

Fire resources and tips

If you have to evacuate

• Cheat sheet: Your very short guide to getting packed up right now to evacuate
• Cheat sheet: A very short guide for how to leave your house if you need to evacuate

If you have more time:

• Every day is now fire season. Let's get you ready for the next wildfire burning near you

Things to consider

• Evacuation terms can be confusing. Here’s what they mean and how to sign up for alerts
• This is why fire officials don't want you to stay and defend your home

Navigating fire conditions

• Cheat sheet: Your very short guide to driving in high winds and fire danger
• High winds and fires mean power outages. Here's how to prep

How to help yourself and others

• Resources for SoCal fire victims, evacuees and first responders
• What to do — and not do — when you get home after a wildfire
• If you want to help fire victims, resist the urge to volunteer
• These are the steps fire victims need to take to make an insurance claim

Understanding how it got this bad

• Yes, wildfires are getting worse. The history that got us to this moment