Spontaneous Combustion in Compost

Bernalillo County Extension Master Composters

Fire in commercial compost
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Albuquerque recently experienced a large fire in a commercial composting facility caused by spontaneous combustion of the compost. Spontaneous combustion in home compost piles is rare. However, the dramatic fire in Albuquerque has inspired us to provide some information about the conditions that might lead to such a fire and how to prevent such a fire.

A fire might occur where the following conditions are met:

  • The pile is large and core temperature reaches 150 F or higher.
  • High summer temperatures and pile heat encourage evaporation of moisture from the setup.
  • Lack of uniform moisture in the pile leads to dry pockets, i.e., combustible material.
  • Wet organics are compacted in the pile, perhaps due to inadequate turning and churning and possibly due to lack of adequate coarse bulking material. This leads to pockets of anaerobic decomposition producing methane gas.

In summary, dry areas (combustible material) plus heat plus methane gas result in flash point which result in fire ignition.

To mitigate the risk of sponaneous combustion:

  • Maintain uniform moisture at all times throughout the decomposition process.
  • Maintain uniform bulking to avoid compaction of wet organics. Bulk as you build.
  • Churn the pile regularly to assist with uniform moisture and bulking distribution.
  • Avoid anaerobic conditions which produce methane gas.
  • Monitor pile temperature. Turn, churn and sprinkle with water to manage too high temperatures in pile.

Always remember, a large burning pile should be managed by fire professionals. If you turn a burning pile, you add oxygen, and the fire will increase.