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City Warns About Fires In Large Compost Heaps

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This compost heap is probably not large enough to spontaneously combust, but should still be properly maintained.

Spontaneous combustion is real, at least when it comes to compost heaps.

Large commercial compost heaps of over 12 feet tall can become dangerous if not properly maintained, says Lauren Hammond, spokesperson for Austin's solid waste services department.

She says, the conditions have to be "just right" for a pile to self-ignite.

The record triple digit heat we've been experiencing can raise the temperature of a compost pile above 160 degrees. Mix that with the various gasses that are released from decomposition and the abundance of dry organic material, and you could have a real fire hazard on your hands.

Though most residential compost piles are no where near 12 feet tall, Hammond says, they still need to be maintained and monitored weekly.

"It's not very typical for small composting piles to combust. Most home compost piles should be about a cubic yard in size, and usually can't get hot enough to combust," Hammond said.

Compost piles need to:

  • Be kept moist, not soaking wet
  • Be turned over and mixed (like a salad)
  • Be kept no larger than 3x3x3 feet (a cubic yard)

Since the pilot program began in October 2009, more than 2,000 people have attended the ongoing free composting classes offered by the city.

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