The answer is not as mysterous as you think. Many cases, if not
all, can be scientifically explained by the "wick effect"
burning.
In cases of SHC, only the body and a highly localized area is badly
damaged, with even the bones turned to ash. COntray to what you
have stated, no, the clothes are also burnt. In some cases, some
areas of the body escape harm while the rest are burnt, a grusome
sight to see two legs or arms sticking out of a pile of
ashes.
Scientists have discovered that most cases of SHC are caused by the
wick effect burning, in which case, the fire is hardly spontaneous,
but rather, having an external cause to start the body burning,
such as a cig or a match.
Experiments with pig bodies to investigate wick effect burning have
produced effects remarkably similar to SHC, with highly localized
area of burn and the bones having being reduced to ash.
What happens is after the person catches fires on his clothes and
collaspes or passes out, the fire contuines to burn. To spark off
wick effect burning, the bodily fulids like fatty tissues and
lipids are melted by the intense heat of the burning and soak the
burning fabric, be it clothes, a sofa or a bed. Hence the fabric
actually becomes a wick that fuels the fire with the body fulids
like a candle. This flames will be small but intense at about 800
degrees, and with the ability to reduce the body to ashes.
After 4-6 hours of burning, the bone marrow, which is high in fat,
melts and soaks the bone, catching fire and allowing the bone to
catch fire, also with wick effect burning. This flame is also
intense enough to reduce the bone to powder.
The fire only stops after the body fuels have been used up, and as
the fire is small, it dies out rather then spreading, hence you get
a typical SHC case of highly localized fire damage but little burns
to anywhere else. If the person is lean enough and arranged in the
right position when he dies while on fire, the extremities will
escape the wick effect burning while the rest of the body is
destroyed, leading to a rather disturbing scene of legs sticking
out of ashes.
Hence we have the main reason for most SHC cases, that is, wick
effect burning. Not as exotic as we would have liked (such as
magnetic fields and stuff), but it's the most likely case. So next
time your clothes catch fire, remember to put out the flames or
else you might become the next case of wick effect burning.
Recently, the wick effect burning was shown on CSI when Brown and
Sarah investigate a case of supposed SHC.
