Two different ignition sources combined to cause last August’s Scatter Creek wildfires in Grand Mound, according to Department of Natural Resources documents obtained by The Chronicle through a public records request.
The fires burned more than 400 acres on either side of Interstate 5, including a protected natural area, a historic homestead, several private residences and a business, according to an investigation from the state Department of Natural Resources.
“It was initially believed that the fire east of Interstate 5 was caused by burning embers emitted by the initial Scatter Creek Wildfire (west of Interstate 5),” the DNR’s report reads. “This cause was ruled out due to the location of the origin, wind direction and distance between the fires. It is highly unlikely that this wildfire was caused by long-range spotting.”
Instead, the east-side fire was likely caused by “superheated carbon particles” from a commercial vehicle passing on the freeway, DNR investigators concluded.
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The DNR’s investigation into the portion of the fire on the east side of I-5 concluded in December. While the investigation into the fire on the west side of the freeway is ongoing and expected to be completed this spring, the cause of that fire has been determined to be “an overheated circular saw used during a home renovation project,” according to the DNR’s report.
The West Thurston Regional Fire Authority led the initial attack against the fire, which grew rapidly due to dry, warm weather and unpredictable wind patterns, firefighters said. Crews from the DNR and from fire districts all over the region soon poured into south Thurston County to help and stayed for about a week mopping up hotspots.
“Thirty-one years in the fire service — this is the largest wildland fire I’ve seen on the west side of the state,” West Thurston Fire Authority Chief Robert Scott said in August.
When the fire was out, firefighters turned the investigation over to the DNR, said Capt. Lanette Dyer of the RFA.
“They have the tools and resources we just don’t have,” she said.
According to the DNR’s report, the first fire was reported at 1:33 p.m. Aug. 22 in a “maintained yard” next to a grassy pasture near the intersection of 183rd Avenue and Wakly Lane Southwest near Grand Mound.
As firefighters were battling those flames, drivers on I-5 started reporting a fire on the east side of the freeway at 3:19 p.m.
“The fire advanced to the northeast with 8- to 10-foot flame lengths; the fire initially burned across the Washington Department of Transportation … right-of-way and several unimproved properties before reaching commercial and residential properties along Loganberry Avenue SW,” the DNR report reads.
The east-side fire burned about 30 acres, a business and homes.
A third fire was reported Aug. 23 about 1,500 feet east of the second fire.
“Witnesses near the third fire reported a shift in winds from a southwesterly to a westerly direction and indicated that a significant amount of ash and burning debris generated from the second fire was falling in the vicinity of the third fire,” according to the DNR report.
The high temperature the day of the fire was 83 degrees with wind gusts up to 13 miles per hour. Grasses and other fuels were dry, according to the report.
A few days after the fire, a bystander shared a cellphone video showing the grass on the east side of the freeway catching fire. The video was shot from the 183rd Street freeway overpass. The video confirmed that there were two areas that caught fire at the same time on the east side of the freeway. Witnesses also confirmed wind was blowing northeast at the time, while the second fire started southeast of the first.
“Winds during the fire were consistently blowing to the east and northeast; the Scatter Creek East origin was located a quarter mile south of the most southern portion of the Scatter Creek West fire,” the DNR report reads.
Bob Johannes, who has lived for 24 years in his home on the corner of Loganberry Street and 185th Street Southwest, near where the second fire started, said at the time that he suspected the source came from slowed traffic on the freeway. He suspected a cigarette.
While the fire burned up to his property line, Johannes’ home was fine, which he credited to his green lawn.
“It was well-watered,” he said in August. “That’s why it didn’t burn.”
Investigators evaluated numerous causes, and ruled out all except “superheated carbon particles.”
The investigation concluded that a commercial vehicle slowing due to heavy traffic in the area of the fire likely emitted those particles.