Conveyor belt fires have often been attributed to the heating of accumulated coal fines beneath the belt structure. However, could it be possible that conveyor belt rubber fines produced from friction of the belt in contact with defective rollers or other parts of the belt structure are a self-heating hazard source? The United Kingdom Health and Safety Executive issued a briefing note in December 2012 on the spontaneous heating of piled tyre shred and rubber crumb. This contained information on laboratory experiments that show rubber crumb and tyre shred are more susceptible to self-heating than cellulosic materials (like hay and straw) in conditions of high ambient temperature. No self-heating experiments have been reported for conveyor belt rubber in any form. This paper presents results of adiabatic incubation testing of conveyor belt rubber fines and slack coal fines collected from the immediate vicinity of a recent Queensland underground coal mine conveyor belt heating incident. Incubation test results show that rubber fines generated from conveyor belt friction are able to self-heat from a temperature as low as 84.5 °C. The spongy fibrous form of the rubber fines creates both a high permeability to airflow and a high surface area for oxidation reaction. In addition, the friction mechanism of the conveyor belt rubber fines generation would create an induced temperature required to alter the environmental boundary conditions to the point where self-heating is sustained. When the rubber fines are mixed with slack coal they increase the likelihood of the coal to incubate and create a spontaneous combustion event.