This article deals with an assessment of the influence of oxygen concentration on the composition and amount of combustion products generated in the course of heating coal particles and wood sawdust at 150 degrees C. This was done both with normal air and at 15% oxygen in the air in an isothermal furnace. The generated gases were analyzed by a Fourier Transform infrared spectrometer. Results show that under both conditions, the same substances are formed: water, carbon dioxide, carbon monoxide and aliphatic hydrocarbons. However, the quantities changed. At 21% oxygen, the concentrations of carbon monoxide and methane were higher than at 15% oxygen both in coal and wood. The oxygen concentration was also found to affect the rates of release of CO and CO2. The rate of release of CO was higher at 21% oxygen, but that of CO2 was higher at 15%, indicating two different mechanisms. In all cases, the concentrations of these gases were higher for coal than for wood. The results have implications for the specification of safe conditions of storage of coal and wood substances and the selection of safety measures. (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.