When a material heats up to the point of burning without the drawing in of heat from its surroundings, it is characterized as spontaneous combustion. This form of science can occur through many substances such as paints, oils, sawdust, hay, waste paper, coal, and charcoal. However, this process may not occur if the level of heat drawn or oxidation brought about is minimal, such as in rusting iron. Level of heat generation air supply and the properties of the surroundings are important for this reaction to be successful It is often very hard to study the causes and properties of this reaction because there is usually no remaining material or evidence after the reaction occurs. Some detections though that the fire was indeed caused by spontaneous combustion is increased burning in the center of the fir as opposed to outside. Another form of detection is whether initial attempts to put the fire down only result in re-ignition. Because of its mysterious nature, the control of spontaneous combustion has not yet been mastered. In contrast, there are some ways of limiting the level of its occurrence. The drying of and use of retardants in regards to dry oils has proven to be productive. This is also true of halogen materials and surrounding them around combustible items

Reference:
http://www.tcforensic.com.au/docs/uts/essay6.pdf