If you have evidence that the contents is ash and remains of partially consumed charcoal briquettes that are still "hot," then a self-heating hypothesis could be considered.

The ash is a very good thermal insulator that could keep the "hot" briquettes from losing heat over time. The "pile size" will be a relevant variable, as well as, the ambient temperature and weather conditions. Direct sunlight and summer conditions will help reduce thermal losses from the "pile." Rain will have an opposite effect.

The wind conditions could make for an interesting hypothesis where the ash may be removed from the pile and the "hot" briquettes are exposed to the wind (enhanced surface oxidation and increased HRR) and perhaps increases the bulk density of the briquettes by removing the ash in the void spaces between the briquettes, thus, removing the void spaces.

Self-heating has a higher propensity for thermal runaway if the material in the "pile" is pre-heated above the local ambient temperature.

Using the Scientific Method, you have evidence of the presence of a material that is known to self-heat in your volume of origin. Do you have any evidence that disproves this hypothesis? If not, then you have a valid hypothesis. If it is the only hypothesis, then by definition, it is "uniquely consistent" with the available data and evidence, then this is the most reliable determination. If there are other valid hypotheses (formulated with evidence) where none rise to the level of "uniquely consistent" with the available data and evidence, then the most reliable determination is "undetermined." This is the best that the application of science can do since at any given time, new data and evidence could be produced that disproves the hypothesis or allows the formulation of a different valid hypothesis.

Douglas J. Carpenter, MScFPE, CFEI, PE, FSFPE
Vice President & Principal Engineer
Combustion Science & Engineering, Inc.
8940 Old Annapolis Road, Suite L
Columbia, MD 21045
(410) 884-3266
(410) 884-3267 (fax)
www.csefire.com