Bark Dust Combustion Sparks Tumalo House Fire

A smoky fire that triggered an alarm and awakened some house guests in Tumalo early Sunday morning was sparked by spontaneous ignition of bark mulch, officials said — but the blaze burned through a plastic water line in a wall, helping slow its spread until firefighters arrived.

Pete and Robin Ferryman called Deschutes County 911 dispatchers around 3:45 a.m. to report smoke alarms sounding and the house in the 20000 block of Arrowhead Drive filling with smoke, said Bend Deputy Fire Marshal Jeff Bond. Smoke was seen coming from a stove vent, he said.

The fire was found to be in a wall, in a vertical chase containing utilities and the stove vent duct, Bond said.

An investigation found that bark mulch (also known as bark dust) applied a week ago was in direct contact with the foundation and siding of the house and had spontaneously ignited, spreading to the wall?s interior, the deputy fire marshal said.

Fortunately, a flexible plastic water line in the wall also burned through, controlling the fire until fire crews could open the wall and finish putting it out, Bond said.

Losses were estimated at $25,000 to the home, owned by Blair Halperin, and $2,000 to the contents, Bond said. Deschutes County property tax records show the house was built in 2007.

Just a week ago, two houses at Eagle Crest Resort west of Redmond were heavily damaged in a fire that began in the bark dust surrounding them, though the damage meant investigators could not determine what caused the blaze.

Bond said firefighters recommend use of non-combustible ground covers, such as decorative gravel. If bark dust is used, he said, ?be sure it is well away from structures.?

?If moisture, temperature and wind conditions are just right, bark mulch can and will spontaneously ignite,? he wrote in a news release. ?The occupants of this home were very fortunate that working smoke alarms alerted them to the fire in time to escape.?

While significant fires ignited by spontaneous combustion of bark dust seem to be rare, Bond said, “There may be more than you think. Sometimes they are just not big enough fires to warrant much attention, or they find a cigarette butt in the area and assume that was the cause.”

“As things decay, biological action can create heat,” he said. “If you get the temperatures and the fuel just right, the oxygen, the wind blowing it — this is a little unusual in that it was discovered at night.”

“It has something to do with moisture content — kind of like the hay thing,” Bond added. “If hay has moisture in a certain range, farmers won’t bale or stack it,” to reduce the risk of spontaneous combustion.”