Types of Spontaneous Human Combustion
Despite the mass media's tendency to characterize Spontaneous Human Combustion as "a person who bursts into flames," SHC actually describes a large group of occurences that has distinct types and variations. This fact is important because while some types of the phenomena may have been explained, others definitely have not. Here are the groupings that I percieve these cases breaking into:

While no cases fall into both major types (how could they?), some cases do fall into more than one sub-type within a type.

Type 1: The Fatal Cases
Fatal cases of Spontaneous Human Combustion represent three-quarters of all cases I have encountered in my research. This is understandable. Where no victim is left to explain what happened, there is room left open for mystery; and, in a majority of these cases, there was no witness to the actual event itself other than the victims. In this group of cases there appears to be three major sub-types that encompass most, but not all, of the cases.
The largest and most publically recognized sub-type of SHC cases are the "Classic Burnings" or "Bedroom Burnings". Classic Burnings are characterized by five main features:

	1)	The victim's body and clothing is mostly reduced to ash.
	2)	Small portions of the body (an arm, a foot, maybe the head) remain unburned.
	3)	Only objects immediately associated with the body have burned; the fire never spread away from the body.
	4)	A greasy soot deposit covers the ceiling and walls, usually stopping three to four feet above the floor.
	5)	Objects above this three to four foot line show signs of heat damage (melted candles, cracked mirrors, etc.); objects below this line show no damage.

These are the cases that are most commonly covered by popular media, and these are what most people think of when they think of SHC. This attention is most likely due to the number of these cases -- fully one half of all cases I've documented -- and the fact that these cases tend to be the most easily explainable, making them the focus of attention by skeptics. But more on that later.
The next largest sub-type of cases are the Witnessed Combustions... cases when people are actually seen by witnesses to explode into flame; most commonly, the witnesses agree that there was no possible source of ignition and/or that the flames were seen to erupt directly from the victim's skin. Though more uncommon than the Classic Burnings, these cases are more evidentially interesting in the argument for SHC. Unfortunately, most of the known cases of this type are poorly documented and basically unconfirmed.
The last, and smallest, sub-type of the Fatal Cases are the Selective Burnings; "selective" because, while the victim has burned to death, objects associated with the body that should have burned also -- the victim's clothing, a chair the victim was found in, etc. -- are undamaged. Again, these cases are evidentially promising if confirmed; but, again, they tend to be poorly documented.

Type 2: The Non-Fatal Cases
The remaining one-quarter of the cases of Spontaneous Human Combustion I have found in my research involve non-fatalities. Unfortunately, the victims of these events generally have no better idea of what happened to them than do the investigators; but the advantage to this grouping is that a survivor can confirm if an event had a simple explaination or not. Thus, there are far fewer cases of SHC with survivors that can be explained away by skeptics without a second look.
As with the Fatal Cases, I see three major sub-types in the Non-Fatal Cases. The first sub-type are those exhibiting Mysterious Flames, representing a little over half of the known Non-Fatal Cases. This feature might sound obvious at first; after all, SHC is, by definition, people burning. As it turns out, however, a large number of accounts attributed to Non-Fatal SHC do not actually involve any form of witnessed flame... thus, the next two sub-types.
The second sub-type of the Non-Fatal Cases are the cases characterized by Mysterious Burns. In these cases, the victims develope burns on their bodies that have no known external cause. These strange wounds commonly start as small discomforts that slowly grow into large, painful marks.
The last sub-type of Non-Fatal Cases are those that exhibit Mysterious Smoke. In these odd and rare occurences smoke is seen to emanate from a person, with no associated fire or source of smoke other than the person's body.
In addition to these three sub-types, there are also certain repeating features that are common to two or more of the Non-Fatal Cases. I make note of these features for two reasons. First: it's possible that these are the faint glimpses of new sub-types that will be seen in the future. Second: it's equally possible that these features are evidence of an urban legend that's being spread with the accounts (an urban legend is a story that's not true, but that continues to be passed on with changes in the details).
The first of the two features I want to point out is the repetition of the "Flaming Fingers" motif in three (?) of the accounts... this feature is especially suspicious because, out of the three cases, two are uncommonly close in time of occurence; if it was a genuine but rare feature, the three accounts would be expected to be spread further apart from one another. Though this is not damning, these cases will require further investigation.
The second feature is the idea of a person with an abnormal control and/or resistance to flame, an idea I refer to as the "Firestarter" motif, after the Stephen King novel of the same name. At the moment there are only two accounts of this type, and they need investigation not only of the singular events that got them onto the SHC list, but also separate investigation of the more general claims of their abilities to control and/or resist fire.