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FIREWALKING
Brian Casaday
Cody Heslington
Introduction
• Firewalking has been practiced for thousands of years by people
from all parts of the world. It is observed as an organized event in
many different cultures and religions. It is by some, thought to be a
paranormal phenomena accomplished only by those of high spiritual
faith or of those who claim total mind over body control.
• The objective of our project is to scientifically explain why firewalking
is possible. We will do this through the use of heat transfer
principles and equations
Why the Foot Doesn’t Burn
• The thermal conductivity of coarse charcoal is
very small and that of skin or flesh is only about
four times more (the thermal conductivity of most
metals is several thousand times larger)
• Charcoal has a very low heat capacity
• Because of the coarseness of the charcoal and
how the foot is placed when walking, not all of
the foot is in contact with the charcoal the whole
time.
• Layer of cooler ash on top of coals acts as
insulation (low conductivity)
• Body has high heat capacity
The Problem
• Calculate the change in temperature of the bottom of
the foot after being in contact with hot charcoal for a 3
second period.
Assumptions:
• Values obtained online for skin density and heat
capacity are correct.
• Equations used in the calculations are legitimate for the
application.
• Preface: This is a fairly complex heat transfer problem
to model accurately. The methods used may not be
exact but will provide a good approximation
The Set-up
• Use thermal resistance method to determine heat
transfer into the foot and ultimately change in bottom of
foot temperature
• Find all values necessary for calculation (i.e. thermal
conductivities of charcoal and human tissue)
• Calculate resistance values for both skin and thin fat
layer beneath skin
• Calculate increase in foot surface temperature. Evaluate
value for significance
The Set-up
q
Tash  T foot
Rskin  R fat
* A foot
Calculations
q
Results
• Our calculations show that after 3 seconds of
contact with the coals the temperature change is
only 8 degrees Kelvin. This is not a large enough
increase to cause a significant amount of pain.
813.48 J
T 
 8.04 K
.0305kg * 3317.5 J /( kg  K )
Conclusion
• Firewalking of a short length is something
any physically fit person could do and
does not require a particular state of mind.
• It is the short time of contact and the low
thermal capacity and conductivity of the
coals that is important.
Appendix A
• References
-Howstuffworks.com, Marshall Brain
http://people.howstuffworks.com/firewalking.htm
-Firewalking
– Myth vs. Physics, David Willey
http://www.howstuffworks.com/framed.htm?parent=firewalking.
htm&url=http://www.pitt.edu/~dwilley/Fire/FireTxt/fire.html
Appendix B
• Detailed Solution:
Tash  T foot
q
Rskin  R fat
Rskin
Lskin
.001m


 .0027 m 2  K / W
k skin .37W / m  K
R fat 
q
* A foot
L fat
k skin
.002m

 .0054m 2  K / W
.37W / m  K
477 K  305 K
.0027 m 2  K / W  .0054m 2  K / W
* .02m 2  271.1584W
qtotal  q * time  271.1584W * 3 sec  813.48 J
qtotal  mcT
qtotal
T 
mavg * c p ,avg
mavg 
(mskin  m fat )
2
mskin   skinVskin  1010kg / m 3 * (.00158mdeep * .02m 2 )  .0319kg
m fat   fatV fat  920kg / m 3 * (.00158mdeep * .02m 2 )  .0291kg
.0319kg  .0291kg
mavg 
 .0305kg
2
c p , skin  c p , fat 3662  2973
c p ,avg 

 3317.5 J /(kg  K )
2
2
813.48 J
T 
 8.04 K
.0305kg * 3317.5 J /( kg  K )
Appendix C
List of Values Used in Calculations:
•
•
•
•
•
•
THERMAL CONDUCTIVITY (W/m · K )
kskin = .37
kcoal = .1
kash = .08
kfat = .2
Kair = .044
•
•
•
•
•
•
LENGTH OF MATERIAL (meters):
Lskin = .001
Lcoal = .01
Lash
= .02
Lfat layer = .002
Lair
= .01
TEMPERATURES OF MATERIALS ( °C):
Tcoal = 538 °C (1000 °F, 811 K)
Tash = 205 °C (400 °F, 478 K)
Tfoot,i = 32.2°C (90 °F, 305.2 K)
SURFACE AREA OF FOOT = .02 m2
DENSITY OF MATERIALS (kg/m3):
ρfat ≈ 920
ρskin ≈ 1010
ρavg ≈ 965
HEAT CAPACITY OF MATERIALS (J/kg ·K)
cp,fat = 2973
cp,skin = 3662
cp,avg = 3318