Spontaneous Human Combustion Humans tend to think of fire as occurring at a high temperature, as when the process is going full bore this is indeed the case. High temperatures are not required to start the combustion process, which is but a chemical process, though high temperatures most often result.
Many chemical reactions give out heat, a byproduct in excess during the molecular rearrangement.
Many combustion processes also occur in a finite or limited manner, and may go unnoticed. A limited combustion process is what keeps the human body at 98.6 degrees, for instance - a slow burn. Oxygen is present in the blood due to the bellowing action of the lungs, and fats or sugars present from stores in the liver or as a result of digestion. The components for a fire hotter than 98.6 are therefore present, but are held in check only by the limited supply of oxygen. Damp a fire and its pace becomes controlled.