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Linseed oil possibly to blame for San Tan Valley house fire

Smoke detectors saved residents
While the cause of the fire has not been officially determined, Rural Metro says it looks like...
While the cause of the fire has not been officially determined, Rural Metro says it looks like linseed oil-soaked rags might have spontaneously combusted. It’s a known danger with linseed oil.(Arizona's Family)
Published: Apr. 26, 2022 at 9:29 AM MST|Updated: Apr. 26, 2022 at 6:36 PM MST
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SAN TAN VALLEY, AZ (3TV/CBS 5) – Investigators say shop rags coated with linseed oil might be to blame for a late-night house fire in San Tan Valley and working smoke alarms saved the residents’ lives. Rural Metro Fire San Tan Valley posted photos from the scene on Facebook Tuesday morning. The fire happened shortly after 11 p.m. Monday in the Whitewing neighborhood, not far from San Tan Foothills High School.

Firefighters believe the fire started in the garage and then spread to the attic. Rural Metro said crews had to take defensive positions outside the house. Drone video from the scene showed gutted rooms and a partially collapsed roof.

From the Arizona’s Family drone

The agency said residents had working smoke alarms that went off and gave them the time needed to get outside safely. Fire safety experts always say having working smoke detectors is the best thing a family can do to protect themselves in case of a fire.

The homeowner tells Arizona’s Family that he is grateful his family was able to get out safely. He also says his neighbors have been very helpful and supportive.

Why linseed oil can be dangerous

While the cause of the San Tan Valley house fire has not been officially determined, Rural Metro says it looks like linseed oil-soaked rags might have spontaneously combusted. It’s a known danger with products that contain linseed oil like wipe-on wood stains and finishes. According to a safety document Rural Metro linked to in its Facebook post, these products don’t dry through evaporation like paint. They dry through oxidation, which is a chemical reaction that generates heat. That heat can be enough to start a fire without a spark or flame. Rags used to apply a linseed oil product can smolder for quite some time before the fire is visible.

The homeowner says he was using rags with linseed oil on his boat and put the rags in a pile around 6 p.m. By 11 p.m, he and his family woke up to the smoke detectors going off.

“The heat that’s generated from that drying process within the materials, the rags, it’s been sealed in an area that is flammable, those combined makes it dangerous,” said Shawn Gilleland with the Rural Metro Fire Department. “If you take that heat and you put in a pile of rags in a bucket or something like that, the heat builds up. Obviously, we already had warmer temperatures out there currently so that added with the drying and the heat created from that evaporation process in the chemicals can actually light whatever material, like the rags, on fire and then spread from there.”

Resource: How to dispose of linseed oil rags (WoodworkingClarity.com)

“In many cases of spontaneous combustion of drying oils, the cause has been a pile of oil-soaked rags,” the document explained. “As the oil oxidizes it generates heat. The rags act as an insulator, allowing the heat to build up until the cloth smokes and eventually ignites. The bigger the pile, the greater the possible heat and the greater the risk.”

Gilleland said there is a way to safely discard rags that are coated with linseed oil.

“In a can, like a metal coffee can or something that’s sealed tight, like a fireproof container, or lay them out until they’re dry fully on a surface that’s not combustible,” Gilleland explained.

San Tan Valley Crews responded to the Whitewing neighborhood last night for this house fire. Crews were forced to...

Posted by Rural Metro Fire San Tan Valley on Tuesday, April 26, 2022

San Tan Valley in Pinal County is a little more than an hour southeast of Phoenix.