[greenyes] backyard compost catching fire?

[Sharon_Gates@no.address]

I just spoke with a Long Beach resident who reported that her backyard 
compost had apparently caught fire.  She had been using a BioStack 
composting bin for about 10 years, and about a month ago moved it to a new 
location under an orange tree.  This morning as she was watering her 
plants, something looked strange, and she realized that the bin was no 
longer there.  Upon investigation, she found melted plastic surrounding 
some composting material, dry & dead leaves on the orange tree immediately 
above the bin, half a camelia bush next to the bin burned away, and potted 
orchids next to the bin with half of their pots melted away.  She said she 
checked the branches of the orange tree, and the heartwood was fine -- 
only the leaves burned.  This led her to conclude that the tree was 
subject to brief, intense heat.  She was also mystefied by the lack of 
evidence of the bin lid anywhere.  The melted plastic surrounded her 
compost like a melted candle, there was nothing on top where the lid would 
have been.

I asked her what she had been putting into her compost, and it was just 
the usual sort of things -- yard trimmings, kitchen scraps.  She said she 
doesn't put grass clippings in because of the weeds and she didn't think 
her pile heated up enough to kill the weed seeds :-).  So it didn't sound 
like she was overloading the pile with nitrogen, and the pile couldn't 
have been too big because it was in a bin.  Suspecting arson, I asked if 
anybody might have access to her backyard.  She lives in a nice part of 
town, and her yard has a gate, so this seems very unlikely.  The only 
explanation that makes sense to me is that something smoldering was put 
into the bin.  She said she watered the pile yesterday, but I think it's 
remotely possible that she missed whatever was smoldering.

Anybody have experience with a small pile like this catching fire?  I 
would have thought it impossible, and yet, there it is.  Spontaneous 
compost combustion?

Sharon Gates
Recycling Specialist
City of Long Beach, California
562/570-4694