PARK CITY, Kan. (KAKE) - It's been well over a week since the massive fire at Evergreen Recycle that briefly threatened a nearby neighborhood. Now, investigators say they've finally determined a cause.

"There was nobody that discarded a cigarette. There wasn't a lightning strike. There wasn't anybody that walked by with a molotov cocktail or anything like that," said Sedgwick County Fire Marshal Bradley Crisp.

Crisp has been hard at work for more than a week trying to figure out what caused the massive fire at Evergreen Recycle.

"The heating started internally in one of the piles of material that were out there," said Crisp.

Surveillance video on the night it started shows that at 6:21 pm, you can't see anything happening. Six minutes later, you can see light smoke coming from one of the wood piles. At 6:36 pm, the smoke turns into a glow, and finally at 6:52 pm, it's a full-fledged fire.

Crisp says after speaking with dozens of people and watching hours of the footage, there's no doubt – this was nothing more than spontaneous ignition.

"Spontaneous ignition is basically where he collects and gathers over a period of time. It's unable to dissipate because of, you know, the material that's stored on top of it," said Crisp. "It stays inside, and it just continues to smolder until it reaches its ignition temperature."

Crisp says during Evergreen's fire inspection in June, his team didn't notice any code violations. But now, he says that's not the case.

"When our crews responded in the evening of October 30th, the pile was a little too high. We estimated the height at about 35 feet. That's about 10 feet higher than it should have been," said Crisp.

Crisp says another clear violation was the fire lanes between the piles. Per code, he says they're supposed to be at least 40 feet wide.

Crisp says owner Jeff Ralls has been cooperative, and even played a crucial role in helping firefighters control it by hopping on a bulldozer himself to move the burning material. He says he has no doubt Ralls will quickly fix the two code violations.

"He's obviously agreed to address those. And we're going to be doing inspections down there a little more frequently. We told him we'd be out there quarterly to kind of check up on that," said Crisp.

KAKE News reached out to Ralls for this story, and he declined to comment.

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The cause of the fire that burned for seven days at Evergreen Recycling has been determined to be spontaneous combustion.

Sedgwick County Fire District 1 has announced that after watching hours of video and speaking to dozens of people, the only cause that could not be ruled out was spontaneous combustion. Spontaneous combustion happens when materials with a low ignition temperature self-heat and catch fire.

On Oct. 30 the most northern pile of debris at Evergreen Recycling spontaneously combusted, causing a much larger fire that burned for seven days. Firefighters were able to leave the scene on Nov. 8 after an estimated $1 million worth of raw wood products was burned.