The source of the Marshall fire was determined to be two points, but investigators found insufficient or no evidence of criminal intent.
Boulder County Sheriff Curtis Johnson said in a Thursday press conference that investigators determined that the fire originated from a buried fire that was lit on a private property six days prior to the fire and an unmoored powerline maintained by Xcel Energy.
“While it took time, I can confidently say we know what happened and why,” Johnson said of the 18-month investigation.
Boulder County District Attorney Michael Dougherty said during the same press conference that no criminal charges would be filed against either property, as there was insufficient or no evidence of criminal or reckless intent.
The Marshall fire broke out south of Boulder on Dec. 30, 2021 amid persistent and extremely high winds focused close to the base of the foothills. It ultimately destroyed 1,084 homes and seven commercial structures, damaging another 149 homes and 30 commercial structures.
Two people died in the fire, one in the Marshall area and one in Superior.
According to Johnson, the first ignition source for the fire was at 5325 Eldorado Springs Drive, the Twelve Tribes community, from a buried fire that had been lit on Dec. 24. A community member called with concerns about the fire on Dec. 24 and firefighters responded, according to the investigation summary and review.
On that day, the weather was cool, rainy and overcast, there was a water source nearby and the residents planned to bury the fire with dirt. Around 5 p.m., the fire had burned down to coals and a resident covered the fire with dirt — but did not add water to extinguish them.
Residents said they never saw smoke or other indications the fire continued to burn. According to investigators, the extraordinarily high winds on Dec. 30 uncovered the buried fire and exposed still-smoldering embers to fresh oxygen. According to fire experts consulted during the investigation, under certain conditions buried fires can continue to smolder for weeks or even months.
Investigators found no evidence that residents started any other active fires between Dec. 24-30. Once the residents spotted the fire on their property, they also tried to extinguish the fire but it was quickly carried away by the high winds.
A burning shed on the property, which went viral at the time as the potential source of the fire, was found to have no electrical wiring and was not on fire when responders first arrived on the scene.
As for the second ignition point, investigators pinpointed the start to the Marshall Mesa trailhead. The most probable cause was found to be hot particles discharged from Xcel Energy power lines.
The county’s initial investigation focused on the possibility that the second fire was caused by an ember cast from the Eldorado Springs Fire, but it was determined that it was highly improbable that an ember could have traveled over 2,000 feet against prevailing winds to start a second fire.
While there were some reports of downed power lines, the only line that went down on Dec. 30 was a communications line that investigators determined did not carry sufficient electrical current to have started a fire.
Using a motion-activated trail camera, a series of photographs showed that between 10:30-11:10 a.m. on Dec. 30, one of three Xcel power lines that run across the top of power poles along the highway came unmoored and sagged low enough to contact a support brace. Investigators found “significant evidence” of electrical arcing.
Tyler Bryant, a spokesperson for Xcel Energy, said in an emailed statement that the company believes the second fire burned in an area already burned by the first ignition and did not cause damage to any homes or businesses.
“We strongly disagree with any suggestion that Xcel Energy’s power lines caused the second ignition, which according to the report started 80 to 110 feet away from Xcel Energy’s power lines in an area with underground coal fire activity,” he said. “Xcel Energy did not have the opportunity to review and comment on the analyses relied on by the Sheriff’s Office and believes those analyses are flawed and their conclusions are incorrect.”
According to the county’s report, Xcel Energy received an opportunity to meet with investigators and provide information, but the company did not produce data or evidence that caused investigators to change their conclusions.
However, investigators found no evidence of criminally negligent or reckless system design or maintenance. It appears the extraordinarily high winds cause the powerline to disconnect and contact other lines, discharging hot particles into a receptive fuel bed.
“We have reviewed our maintenance records and believe the system was properly maintained,” Bryant said. “We operate and maintain our electric system consistent with leading energy service practices and we’re proud of our employees and the work they do to deliver safe, reliable and clean energy to our communities.”
Johnson and Dougherty added that an underground coal fire as the source of ignition could not be ruled out. The specific coal seam running under the Marshall Mesa trailhead is actively burning, but the vents investigated did not have the conditions required to ignite a surface fire.
Doughterty emphasized that in either situation, the district attorney’s office would not have sufficient evidence to pursue a criminal investigation.
“A judge would dismiss this prosecution for not having enough evidence,” he said.
He did also note that a civil process does not have the same strict requirements, and that if additional information comes to light from civil litigation related to the fire his office would review and reconsider the evidence.
The investigation did not determine when or where the two fires might have merged.
A recording of the press conference will soon be available to the public on the sheriff’s office website, along with all investigation materials.
