Lignocellulosic biomass from industries such as plywood manufacturing, pulp and paper production, and solid and liquid fuel generation often involves large-scale processing and storage of raw materials like woodchips, sawdust, and pellets. A significant issue in these industries is that biomass can spontaneously heat up and generate toxic and combustible gases. In extreme cases, this can lead to explosions, fires, and poisoning, particularly in silos. While the precise mechanisms behind heat generation and off-gassing are not fully understood, it has been suggested that abiotic chemical reactions, particularly those involving fatty acids, play a key role.We have studied the off-gassing of various sawdust fractions in pelletized form and found that methane, carbon dioxide, and carbon monoxide were produced during storage under laboratory conditions with oxygen consumption. Although fatty acid content showed some correlation with gas formation, adding fats did not significantly accelerate the process. Notably, sapwood (the living part of the wood) produced much stronger gas emissions compared to dead sapwood, which emitted very low amounts of gas. While heat generation was not detected under lab conditions, field experiments with large stacks of pellets revealed a connection between gas formation and heat generation.For freshly chipped juvenile sapwood, rapid heat formation was also observed in lab-scale experiments, associated with gas development. However, for stored material, this effect was much weaker. We hypothesize that carbon monoxide and heat formation are stress responses from the living parenchyma cells in the sapwood, while methane is a product of fermentation in the same cells. Thus, we propose a biological, rather than abiotic, explanation for at least part of the phenomena.