It would seem that this expert is turning the Scientific Method on its head. "Can not be eliminated ..." is a refrain that is all to common and by itself, is not a reliable application of the SM.

For scientific reliability, one needs evidence to formulate (different than "considering" a hypothesis) a hypothesis and evidence to disprove the hypothesis. By just saying that a hypothesis cannot be eliminated is not evidence. It is actually, a lack of evidence. You cannot "rule out" a hypothesis that cannot be first, "ruled in." So what is the evidence that self-heating occurred in this specific incident?

What is missing from the description of self-heating are the relevant conditions required for self-heating to occur AND the occurrence of thermal runaway. At a high level, there is a critical pile size required for any given ambient temperature. There is also a critical temperature required for any given pile size. The pile size and temperature are highly coupled for the self-heating to thermal runaway phenomenon. So what evidence is there that this configuration and conditions are sufficient for this to occur in this specific incident?

I am not aware of any data that would allow a determination of the thermal decomposition rate of tree roots within a wall. An order of magnitude estimate based on other moist bulk materials that are subject to bio heat generation would suggest that the pile size and temperatures are well outside the conditions necessary for any significant self-heating. Critical pile sizes for wood chips are orders of magnitude larger than the pile size of tree roots in a wall. To say nothing of the fact that three roots are solid and do not generally behave like a porous pile of bulk materials such as wood chips or sawdust.

Douglas J. Carpenter, MScFPE, CFEI, PE, FSFPE
Vice President & Principal Engineer
Combustion Science & Engineering, Inc.
8940 Old Annapolis Road, Suite L
Columbia, MD 21045
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