Spontaneous Human Combustion occurs because the body is in an acidic condition when burning fat, which may be burned naturally otherwise like an engine burns fuel, with flatulence "letting off steam", although instead of emitting fumes, the fat ignites within the body.
SHC occurs because the body does not properly transform fat into gas. The fat ignites internally due to the combinations of chemicals which become flammable in an acidic system which becomes a thermal conductor. The actual immolation is a smoldering effect, although if intense enough, clothing and furniture materials may ignite.
SHC occurs in a highly acidic, low metabolism system, where an "inner burn" may occur. The fat burns / feeds upon itself, with purported "smoke" exiting the pores. SHC occurs when the body is unable to produce normal emissions. SHC occurs between thermal transference of fat into farts.
With the exception of 'gas-ex' products or poppy seed treatment to naturally and safely suppress flatulence, the key phrase is "fart or burn". It behooves a healthy individual to let loose a hearty fart whenever possible, with obvious precautions towards social consideration of course. ∞
Addendum: As a experiment, I once cast a Curse upon a truly deserving disturber to be immolated in this manner. As a result, there was a mysterious 'fire' in her office, which also destroyed certain documentation which was specified in the parchment formerly contained upon a computer. Further details to be divulged upon revelation.