Upper Marlboro, Md, (WUSA) -- Fire authorities in Prince George's county say "spontaneous combustion" may be the cause of a fire that consumed a 2 acre pile of mulch stored at the Ritchie Landfill on Ritichie Road.

The fire is declared extinguished but site continued to smolder Friday and was being monitored, according to Mark Brady, spokesman for the Prince George's County Fire/EMS service.

The fire, in a pile that was at least 50-feet high, started Wednesday and took more than 24 hours to extinguish.

Mulch naturally generates high temperatures because it is made up of decaying organic materials. The heat in the very large pile may have been enough to cause spontaneous combustion, according to fire officials, who have not made a final determination about the cause.

Fire officials say spontaneous combustion is not a hazard in mulch that is spread at home as landscaping material.

However, dry mulch can be a fire hazard particularly in drought conditions, according to the online magazineFire Engineering.

Such fires are most often caused by cigarettes discarded in dry mulch. Pine bark and cypress bark mulch are the mostflammablebecause of the pine pitch in the material. Shredded hardwood, which is more common in the DC region is lessflammable.

Fire Engineering offers a number of prevention tips including:

  • avoiding mulch spread within 18" offlammablebuilding materials.
  • keeping mulched areas moist
  • avoiding the discard of smoking materials in mulch areas
  • ensuringelectricalwires and fixtures in mulched areas are rated for outdoor use.
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