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Officials still aren't sure what caused the Tunnel Fire; most causes ruled out

An investigation into last year’s destructive Tunnel Fire that destroyed dozens of buildings northeast of Flagstaff shows that investigators were able to rule out most causes for the fire. 

The U.S. Forest Service released its eight-page synopsis of the Tunnel Fire’s investigation to KJZZ’s Fronteras Desk Thursday. KJZZ News obtained the report under the Freedom of Information Act.

The report shows that by the time investigators were able to examine the fire’s origins, the area had been disturbed by firefighting suppression operations. 

Smoking or an unspecified incendiary device are listed as possible causes. But it’s only a circumstantial reasoning, no cigarettes, matches, illegal substances or pipes were found in the area. Campfires, lightning strikes, and five other causes such as grinder sparks or fireworks were ruled out. 

The fire was first reported April 17 at about 4:14 pm by a couple driving on forest roads who spotted smoke near Forest Service roads 420 and 6064D. The reporting parties say a 30-foot downed tree on fire, according to the report. About 25 minutes later, another witness called 911 to report smoke. This pair of witnesses saw two UTVs drive past the fire but did not stop and then spotted a pickup truck in the area.

At that point, more smoke reports came in to 911. When Coconino County Sheriff's Office deputies, Summit Fire department personnel and Forest Service crews arrived, the Tunnel Fire was 1-2 acres, "actively burning in grass and down timer with light winds."

The report says the fire was first investigated by a fire prevention technician with the Forest Service on April 17 and 18 and then it was released to firefighting operations. During a townhall following the blaze, residents had asked how a fire that was being monitored by the Forest Service could leap out of control.

"The fire was named the Tunnel Fire and was left in containment status with fire line completely around the fire’s edge on the evening of April 18, 2022," the report states.

Then on April 19 at 7:47 a.m., the fire jumped containment. 

Over the next two days investigators reviewed video of the fire taken by witnesses when it first started. 

A week later, a new investigation into its origins was launched based off video footage from a witness when it was only about 900 square feet in size. But the origins of the fire had been heavily disturbed by firefighting operations. 

Eventually, the specific origin area of the fire was located. But no evidence was discovered as it was also heavily disturbed. And investigators weren't able to pinpoint the precise spot where the ignition source first met the forest. 

As a result, investigators ruled out lightning, campfires, machinery, burned debris, children, the railroad, and even miscellaneous potential causes like spontaneous combustion or target shooting. 

Smoking or an unspecified incendiary device are listed as possible factors. A smoke report was called in at 4:28 pm but the report doesn't specify whether the smoke report was a complaint about cigarettes or something else.

No cigarettes, pipes, illegal substances or matches were found within the area of the fire's origin. 

KJZZ News has filed a new records request for the complete investigation. A spokesperson estimated it will take more than a year to obtain the full report.

Investigators obtained a warrant for cellphones used within the area; it shows only one cellphone in the area and that belonged to the first witness to call it in. 

Fronteras Desk senior editor Michel Marizco is an award-winning investigative reporter based in Flagstaff.