Firewalking has been practiced by
many people and cultures in all parts of the world, with the earliest known
reference dating back to Iron Age India – c. 1200 BCE. It is often used as a
rite of passage, as a test of an individual's strength and courage, or in
religion as a test of one's faith. Firewalking became popular in the twentieth
century when author Tolly Burkan
began giving public classes
throughout the United States and Europe in an effort to demonstrate that the
practice was not paranormal. (Thank God for
the Internet, we can now verify things like who was the first introduce something to North America. As well as the science involved.)
Today,
it is often used in corporate and team-building seminars and self-help
workshops as a confidence-building exercise. Firewalking is frequently held to imply that the feat requires the
aid of a supernatural force, strong faith, or on an individual's ability to
focus on "mind over matter".
Modern
physics has explained the phenomenon, concluding that the amount of time the
foot is in contact with the ground is not enough to induce a burn, combined
with the fact that coal is not a very good conductor of heat.
Explanation
When two bodies of
different temperatures meet, the hotter body will cool off, and the cooler body
will heat up, until they are separated or until they meet at a temperature in
between. What that temperature is, and how quickly it is reached, depends on
the thermodynamic properties of the two bodies. The important properties are
temperature, density, specific heat capacity, and thermal conductivity.
The square root of
the product of thermal conductivity, density, and specific heat capacity is
called thermal effusivity, and tells how much heat energy the body absorbs or
releases in a certain amount of time per unit area when its surface is at a
certain temperature. Since the heat taken in by the cooler body must be the
same as the heat given by the hotter one, the surface temperature must lie
closer to the temperature of the body with the greater thermal effusivity. The
bodies in question here are human feet (which mainly consist of water) and
burning coals.
Due to these
properties, David Willey, professor of physics with the University of Pittsburgh, says he
believes firewalking is explainable in terms of basic physics and is not
supernatural nor paranormal. Willey notes that most fire-walks occur on coals
that measure about 1,000 degrees Fahrenheit (550 degrees Celsius), but he once
recorded someone walking on 1,800-degree (1,000 °C) coals.
Additionally, it is
postulated that walking over hot coals with wet feet may insulate the feet due
to the Leidenfrost effect. Ash buildup on
the coals can also provide an insulating layer.
Factors that prevent burning
·
Water has
a very high specific heat capacity (4.184 kJ/K kg), whereas coals have a very
low one. Therefore the foot's temperature tends to change less than the coal's.
·
Water
also has a high thermal conductivity, and on top of that, the rich blood flow
in the foot will carry away the heat and spread it. On the other hand, coal has
a poor thermal conductivity, so the hotter body consists only of the parts of
the coal which are close to the foot.
·
When the
coal cools down, its temperature sinks below the flash point, so it stops
burning, and no new heat is generated.
·
Firewalkers
do not spend very much time on the coals, and they keep moving.
·
Calluses
on the feet may offer an additional level of protection, even if only from pain;
however, most people do not have calluses that would make any significant
difference.
Risks when firewalking
·
People have
burned their feet when they remained in the fire for too long, enabling the
thermal conductivity of the coals to catch up.
·
One is more
likely to be burned when running through the coals since running pushes one's
feet deeper into the embers, resulting in the top of the feet being burnt.
·
Foreign
objects in the coals may result in burns. Metal is especially dangerous since
it has a high thermal conductivity.
·
Coals which
have not burned long enough can burn feet more quickly. Coals contain water,
which increases their heat capacity as well as their thermal conductivity. The
water must be evaporated already when the firewalk starts.
·
Wet feet can
cause coals to cling to them, increasing the exposure time.
In 2002, twenty
managers of a fast food chain in Australia received treatment for burns caused
by firewalking. [ http://www.theage.com.au/articles/2002/02/27/1014704967158.html ] However,
this exercise in firewalking was practiced over timber, a more efficient heat
conductor than charcoal.
In July 2012, at
least 21 people were treated for burn injuries after taking part in the
crowning event of the first day of a function in San Jose, CA.
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