The Arlington school district will spend $200,000 replacing wood chips with pea gravel at 35 playgrounds in response to a fire blamed on spontaneous combustion of the wood fiber, the superintendent said. Surveillance video showed that nobody was around to start the fire at an elementary school playground last week, officials said. The fire melted the plastic and metal equipment, causing $35,000 in damage.
"It was a very unusual occurrence," Superintendent Mac Bernd said Monday. ?The material is designed so it won?t burn.?
Deputy Fire Marshal Keith Ebel said the conditions that caused the chips to catch fire were "like a perfect storm."
Heavy rains earlier this summer saturated the wooden material, which began to decompose in the recent summer heat wave. High temperatures Thursday afternoon then ignited the dry chips on the surface.
"Everything had to be just right for this to occur," Ebel said.
Officials said the fire was like the combustion that can occur with organic material in a compost pile if it is not turned regularly.
The district rakes the playground wood chips every 30 days, but fire officials said heat can build up more quickly than that.
Such combustion would occur only if poor quality material was used, said Mark Carlston, president and CEO of Forest Wood Fiber Products of Lake Elsinore, Calif. The company does not supply wood chips for Arlington schools.
Carlston said problems could occur if the wood fiber contained lumber such as plywood with flammable resins or glues, or if contained ground up tree trimmings or similar vegetation.
"If the material is made correctly, I would say (spontaneous combustion) would be almost impossible," he said.
Bernd said if people had been at the playground they would have likely had to time to escape the fire. The wood fiber discolored and smoked before flames formed.
Ebel said there have been other unexplained fires at playgrounds that might be attributable to spontaneous combustion, but investigators couldn't rule out human intervention.
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