This document: a) specifies a general test procedure for quantification of the spontaneous heat generation from solid biofuel pellets using isothermal calorimetry; b) specifies a screening test procedure for wood pellets using an instrument temperature of 60 °C; c) establishes procedures for sampling and sample handling of solid biofuel pellets prior to the analysis of spontaneous heat generation; and d) gives guidance on the applicability and use of isothermal calorimetry for calculation of the net reaction rate of the heat producing reactions of solid biofuel pellets.