The paper summarises 25 years of experience with pulse flow calorimetry (PFC) as a method to assess the potential of coals to spontaneously heat up using the values of oxidation heat q(30) (W kg(-1)). During the period, about 300 coals of various rank and with natural moisture content were investigated, the maximum propensity to oxidation being found in subbituminous coals with moisture content of about 20%. The highest value of oxidation heat q(30) was found to be 10.5 W kg(-1). Oxidatively altered bituminous coals are presented as coals of evidently increased ability to oxidize, and the reasons for the increased oxyreactivity are reported. Limiting values of q(30) heat are then given to rank the coals according to the categories of self-heating risk. Finally, a comparison between oxidation heat q(30) and the values of the initial rate of heating (IRH) of adiabatic oxidation tests is presented. (C) 2014 Elsevier Ltd. All rights reserved.