Well, I'm no expert, but there are more plausible explanations than someone suddenly bursting into flames.
See: Spontaneous Human Combustion: Facts & Theories
Only about a dozen claimed real-life cases of SHC have been investigated in any detail. Researcher Joe Nickell examined many "unexplainable" cases in his book "Real-Life X-Files" and found that all of them were far less mysterious than often suggested. Most of the victims were elderly, alone and near flames (often cigarettes, candles, and open fires) when they died. Several were last seen drinking alcohol and smoking.
If the person is asleep, intoxicated, unconscious, infirm or otherwise unable to move or put the flames out, the victim's clothes can act as a wick (most people spend most of their time wrapped in flammable clothing made up of cottons and polyester blends). The flames draw on the body's fat (a flammable oil very near the skin's surface which combines with the burning clothing) to fuel the fire.
See: spontaneous human combustion (SHC)
A more economical and reasonable theory of how human bodies burn in rooms without having the entire room engulfed in flames is the idea of the wick effect. The ignition point of human fat is low and to get the fire going would require an external source. Once ignited, however, a "wick effect" from the body's fat would burn hot enough in certain places to destroy even bones. To prove that a human being might burn like a candle, Dr. John de Haan of the California Criminalistic Institute wrapped a dead pig in a blanket, poured a small amount of gasoline on the blanket, and ignited it. Even the bones were destroyed after five hours of continuous burning. The fat content of a pig is very similar to the fat content of a human being. The damage to the pig, according to Dr. De Haan "is exactly the same as that from supposed spontaneous human combustion." A National Geographic special on SHC showed a failed attempt to duplicate the burning pig experiment. However, it is obvious that the failure was due to leaving the door to the room open to the outside, which created a draft and led to the flames igniting everything in the room. Had the room been closed up, as are the rooms in which many of the elderly persons have died in fires attributed to SHC, it is likely that the pig would have smoldered for several hours without the rest of the room becoming engulfed in flames.
And, finally, Not-So-Spontaneous Human Combustion.
There is too much material to post here, but suffice to say that the concept that humans will spontaneously burst into flames is absurd. In the words of Joe Nickell:
It is interesting that the major proponents of SHC --Michael Harrison (Fire from Heaven, 1978), Jenny Randles and Peter Hough (Spontaneous Human Combustion, 1992), and Larry E. Arnold (Ablaze!, 1995) --are all popular writers who are credulous as to other paranormal claims. They stand in contrast to the physicists and chemists, the forensics specialists, and other scientists who question - on the evidence - the reality of spontaneous human combustion.
Joe Nickell is a person whose whole life goal is to deny the existence of just about everything. He has been on all kinds of talk shows and leaves out facts that dont fit his theories.