Heat Release in Thermally Disintegrating Wood


  • Hans Kubler


Pyrolysis, thermal decomposition, exothermic point, self-heating, spontaneous ignition, heat of combustion


Wood contains more energy than do its products of slow pyrolysis. Consequently, slow pyrolysis must be an exothermic process, and cannot consume heat as generally believed. Heat release in experiments with thermally slowly decomposing wood has indeed been reported in the literature. The exothermic nature of pyrolysis explains why wood self-heats when its temperature has been somehow raised above 80 C and when the released heat does not dissipate. This way the temperature may reach the level of oxidation and combustion. Such pyrolytic self-heating occurs in piles of sawdust, wood chips, and bark, in hot-stacked boards and paper rolls, in dryers for veneer and other wood, and in structural lumber near heat sources. In contrast to other kinds of self-heating, pyrolytic self-heating cannot be prevented by exclusion of oxygen: instead the process has to be decelerated by cooling the material.


Aaron, J. R. 1980. The production of wood charcoal in Great Britain. Forest Report No. 121. Gr. Brit. Forestry Comm., London, GB.nBergman, O. 1974. Thermal degradation and spontaneous ignition in outdoor chip storage. Sven. Paperstidn.77(18):681-684.nBrowne, F. l. 1958. Theories of the combustion of wood and its control. For. Prod. Lab. Rep. No. 2136. For. Prod. Lab., Madison, WI.nBrowne, F. l., and J. J. Brenden. 1964. Heat of combustion of the volatile pyrolysis products of fire-retardant-treated ponderosa pine. U.S. Forest Service Res. Paper FPL 19. For. Prod. Lab., Madison, WI.nDemidov, P. G. 1962. Combustion and properties of combustible substance. Izdatel'stvo Minister-stva Kommunal'nogo Khozyaystva RSFSR, Moscow.nGoos, A. W. et al. 1948. Some experiments in sawdust carbonization. Proc. For. Prod. Res. Soc.2:55-59.nHeinrich, H. J., and B. Kaesche-Kirscher. 1962. Contribution to research on spontaneous heating of wood. Brennstoff-Chemie43(5):142-148.nHolmgren, B. 1948. Self-ignition of porous wood fiberboard. Sven. Paperstidn.51(10):230-232.nJach, W. 1973. State of the art on research about biological self-heating. 4. International Fire Protection Seminar 1973 Zurich. Brand-Verhutungs-Dienst fur Industrie und Gewerbe, Zurich, Switzerland.nKlason, P. 1914. Theory for dry distillation of wood. J. Praktische Chemie B90(10+11):413-447.nKlason, P. et al. 1909. Dry distillation of cellulose. Zeitschr. Angew. Chemie22(25):1205-1214.nKlason, P. et al. 1910, Dry distillation of pine, spruce, birch, and beech wood. Zeitschr. Angew. Chemie23(27):1252-1257.nKollmann, F. 1960. Occurrence of exothermic reactions in wood. Holz Roh- Werkst.18(6):193-200.nMacKay, G. D. 1967. Mechanism of thermal degradation of cellulose. Canada Dep. of For. and Rural Dev. Dep. Publ. No. 1201. Forestry Branch, Ottawa. Canada.nMatson, A. F. et al. 1959. Survey of available information on ignition of wood exposed to temperatures. Bull. of Res. 51. Underwriters' Laboratories, Chicago, IL.nMessner, K., and W. Serentschy. 1978. Ecological factors and fungal flora in industrial piles of sawdust. Holzforsch. Holzverwert.30(4):77-79.nMurphy, E. S. 1962. Thermal decomposition of natural cellulose in vacuo. J. Polymer Sci.58(166/1):649-665.nOstlin, B. 1959. Ignition of wood at temperatures below the normal ignition point. Sven. Paperstidn.63(7):225-227.nPlath, E., and L. Plath. 1955. Paper chromatography studies on European beech-steaming condensates. Holz Roh- Werkst.13(6):226-236.nRiley, R. G. 1979. Fires in raw material storage. Pulp Paper53(14):100-103.nRothbaum, H. P. 1963. Spontaneous combustion of hay. J. Appl. Chem.13(July):291-302.nSchaffer, E. L. 1966. Review of information related to the charring rate of wood. U.S. For. Serv. Res. Note FPL-0145. For. Prod. Lab., Madison, WI.nSchaffer, E. L. 1979. Smoldering combustion tendency. Thermal Insulation2(1):135-140.nSpringer, E. L. et al. 1971. Spontaneous heating in piled wood chips. Tappi54(4):589-591.nTsuchiya, Y., and K. Sumi. 1977. Spontaneous ignition. Can. Build. Dig.189:1-4.nWalker, I. K., and W. J. Harrison. 1977. Self-heating of wet wood. New Zealand J. Sci.20(2):191-200.nWidell, T. 1948. Thermal investigation into carbonization of wood. The Royal Swedish Academy of Engineering Sciences, Proc. No. 199. Generalstabens Litografiska Anstalts Forlag, Stockholm, Sweden.n






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