6.2: Can science explain fire-walking?
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This article is from the Scientific Skepticism FAQ, by Paul Johnson Paul@treetop.demon.co.uk with numerous contributions by others.
6.2: Can science explain fire-walking?
There are a number of theories which have been put forward to explain
firewalking. Any or all may be the explanation for a particular
event.
o The dry wood coals used by firewalkers conduct heat very poorly.
The coal itself may be very hot but it will not transfer that heat
to something touching it.
o The coals are a very uneven surface, and the actual surface area of
foot touching the coals is very small. Hence the conduction of heat
is even slower.
o Wood coals have a very low heat capacity, so although they are very
hot there is actually not much heat energy to be transferred to the
foot.
o Firewalkers do not spend very much time on the coals, and they keep
moving. Jan Willem Nienhuys <wsadjw@urc.tue.nl> adds that about 1
second total contact time per foot seems on the safe side.
o Blood is a good conductor of heat. What heat does get through is
quickly conducted away from the soles of the feet.
o The "Leidenfrost" effect may play a part. This occurs when a cold,
wet object (like a foot) touches a hot, dry object (like a burning
coal). The water vaporises, creating a barrier of steam between the
hot and cold objects. Hence the two objects do not actually touch
and evaporation from the cold object is much slower than might
otherwise be expected. Since steam is a relatively poor conductor
of heat the foot does not get burned. Jearl Walker, of Scientific
American's "The Amateur Scientist" column, explains the Leidenfrost
effect in the August 1977 issue; he walked across coals unharmed and
attributes this to the Leidenfrost effect. Other scientists believe
that the Leidenfrost effect is unimportant in firewalking.
Pain perception is not as simple as everyday experience suggests.
Some people experience great pain without any apparent cause.
Others experience little or no pain despite great injury. Cognitive
and emotional factors seem to be important. A belief that one has
control over the pain seems to reduce the level of pain experienced.
Fear seems to increase it.
Firewalking is usually done in a religious or spiritual context. This
would tend to reduce the level of pain experienced by firewalkers
without affecting the amount of physical damage done to the feet.
Some firewalkers put forward mystical explanations of why firewalking
is possible without serious physical harm. A few skeptics have
challenged these firewalkers to stand on hot metal plates instead of
coals. Others have pointed out that making such a challenge in the
belief that the firewalker would be seriously hurt is of dubious
morality.
Jay Mann from New Zealand writes:
The NZ CSICOP had a mass firewalk at its annual meeting in
Christchurch about 5 years ago. We had a lengthy afternoon talk by a
professor of physics, complete with demonstrations of tossing hot
bread loaves back and forth. The fire was built in mid-afternoon, and
the firewalk took place after the society banquet, that is, about 10
p.m.
One *never* walks on live coals. The fire is lit hours before the
actual walk. Large burning coals are removed. The firebed is carefully
raked to provide a continuous smooth layer of ashes over all burning
embers. By this time, it is dark and the firebed is seen to glow
ominously. It is still hot, and potatoes can be cooked in the ashes. On
the other hand, the rate of heat transfer through the ash is
time-limited. If participants take steady strides, even city-folk with
soft soles can manage at least five steps. In the Christchurch version,
we stepped in a small puddle of water at the end of the firewalk; I have
seen at least one description of a "commercial" firewalk where cooling
water was also provided.
In Christchurch, dozens of people went across. Some went back for two
or three passages. The bed was re-raked periodically to restore the ash
layer. There were two or three minor burns and blisters the next day,
mostly people who had kicked embers up between their toes. Having done
a firewalk is a wonderful conversational topic, and most people will not
believe that you didn't have some sort of mystic faith and determination
to "protect" your body.
Denis Dutton, then president of the NZSCICOP, later went to New Guinea
on a professional trip. There he trained one local tribe in firewalking
as way to attract the tourist dollar. The first few firewalkers, in a
private test, were cautious, but eventually the whole tribe-- man,
woman, and child -- gleefully ran through the "fire". For public
performance, the tribe added a lot of magical incantations and rituals.
Denis asked them how they would explain their knowledge of the trick.
They replied that they would say "an alien from the skies came and
taught us". You can imagine that people with tough soles from barefoot
walking could tolerate more exposure soft-soled city people.
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