Assessment of the Self-Heating Potential of Fresh Wood Using the Pulse Flow Calorimetric Method

The self-heating propensity of the fresh wood of ten tree species (two coniferous, eight deciduous) was studied calorimetrically using oxidation heats, q30, at a temperature of 30 °C. Values of q30 in the range between 0.45 W kg−1 (dry) and 1.1 W kg−1 (dry) were found. The lowest evolution of the oxidation heat proved two coniferous wood types—spruce and pine. On the other hand, the highest value of the q30 heat manifested willow wood, which exceeded (as the only one of the samples) the level of 1 W kg−1 (dry). Water was confirmed to promote the generation of oxidation heat, while completely negligible oxidation heat effects were found in dry wood samples. A rise in the heat evolution with increasing moisture content can be explained not only by a change in the mechanistic pathway of the chemical oxidation of wood in the presence of water, but also by the restoration of the activity of microorganisms in wood, which occurs only at a sufficient level of moisture content. Tree bark appears to be probable carrier of a diverse microbiome. Based on the experiments with debarked wood samples, it can be estimated that the part of the heat produced by microorganisms constitutes a remarkable 35–55% of the global oxidation heat q30, as determined for fresh wood samples.