DENVER — The most destructive wildfire in Colorado history was likely sparked nearly simultaneously by an arcing power line and days-old bonfire whipped up by hurricane-force winds, investigators announced on Thursday.
The Dec. 30, 2021, Marshall Fire destroyed more than 1,000 homes in suburban Boulder, along with a hotel and portions of a shopping center, and killed two people along with an estimated 1,000 pets. Investigators and prosecutors on Thursday declined to bring criminal charges, but noted civil lawsuits would likely be filed by victims. Investigators said they don’t believe burning underground coal mines in the area were a factor “but cannot be completely ruled out.”
Few homes have been rebuilt in the $2 billion fire’s aftermath, and thousands of residents of the small communities of Superior and Louisville remain displaced.
“This fire was terribly destructive and traumatic for so many people,” Boulder District Attorney Michael Dougherty said at a press conference. “This community has suffered a lot. Their wounds do not heal today, and likely never will. But as people continue to rebuild, we rebuild as a community.”
How did the Marshall Fire start?
According to investigators, the fire started in two places separated by about 2,000 feet. The first fire start was sparked by a bonfire of railroad ties and other wood that residents had lit on Dec. 24, allowed to burn down to coals, and then covered over with dirt. Winds of 115 mph blew the dirt off the embers Dec. 30, igniting nearby vegetation, Boulder County Sheriff Curtis Johnson said. Johnson was among those who lost homes in the fire.
Dougherty noted the weather Dec. 24 was wet and cold, and that firefighters who had checked on it then concluded the residents’ actions were “reasonable and responsible.” He added those residents immediately tried to control the fire that erupted Dec. 30, including working with firefighters. He said it would be impossible to secure a criminal conviction, given those factors, but also noted civil liability is a lower standard of proof.
The second fire, upwind of the bonfire site by about 2,000 feet, appeared to likely have started when an Xcel Energy powerline blowing in the high wind began arcing and scattered hot aluminum particles into vegetation, Johnson said. Investigators concluded it was unlikely the first fire sparked the second, because the 100-mph winds were blowing embers in the opposite direction.
“The two fires became one at some point,” Johnson said. He said investigators didn’t look at when and how the two fires merged.
Xcel shortly after fire said it had no downed lines in the area, which authorities acknowledge was accurate: The power line was loose and arcing, but not actually touching the ground. Investigators also noted that Xcel immediately repaired the dangling power line, but said that was likely because the company was under significant public pressure to restore power to the area, and not to hide the damage.
What kind of damage did the Marshall Fire cause?
Driven by hurricane-force winds, the fire blasted through multiple subdivisions and jumped a six-lane highway within hours. Many residents were not home at the time of the fire, which erupted midweek and midday. Some watched in horror from roadblocks as their homes burned and propane tanks exploded.
In most cases, firefighters were unable to protect structures because the winds were whipping the flames too high, sending streams of embers from one house to the next. The fire burned itself out the next day as the winds died, and snow and cold temperatures blanketed the area.
While most of the debris has been removed, few homes have been rebuilt, in large part because only about 8% of residents had adequate insurance to cover the replacement costs of their homes, according to state officials. A new state law passed after the fire requires Colorado insurers to explain to homeowners that their policies might not cover replacement costs due to inflation and new building codes.
Why does this fire have national implications?
The Marshall Fire burned in an area that would traditionally have been considered at low risk for wildfire: few trees, low grasses and wide roads to prevent embers from spreading. But experts say climate change is drying out areas that were once wetter and snowier, raising the risk that embers from burning dry grasses whipped by stronger windstorms can blow into suburban areas, triggering a catastrophic fire where houses themselves become the fuel to spread it.
Previously, winter snow would have packed down and soaked the tall grasses.
In California, power line-sparked fires are responsible for multiple deaths, and courts there have held Pacific Gas & Electric responsible. In response, lawmakers have forced PG&E to spend more money trimming branches near power lines, and to also de-energize lines when there’s a high risk of fire in the area.
Insurers are increasingly concerned that wildfires and floods supercharged by climate change are making it too expensive to write policies in areas that were once considered safe.
