(August 14, 2007)--The Arlington school district will replace wood chips with pea gravel at 35 playgrounds in response to a fire blamed on spontaneous combustion of the wood fiber.

Superintendent Mac Bernd says it will cost $200,000.

Officials say surveillance video showed that nobody was around to start the fire at an elementary school playground last week.

Deputy Fire Marshal Keith Ebel say 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.

That process produces heat below the surface and coupled with high temperatures Thursdsay afternoon it was enough to ignite the dry chips on the surface.

Officials say the fire was like the combustion that can occur with organic material in a compost pile if it is not turned regularly.

Fire officials said the surveillance video confirms that other similar fires could have started spontaneously, rather than as a result of arson or an accident.

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