1. FIREWALKING Brian Casaday Cody Heslington

2. 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

3. 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

4. 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

5. 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

6. Calculations q The Set-up

7. 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.

8. 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.

9. 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

10. Appendix B Detailed Solution:

12. Appendix C List of Values Used in Calculations: THERMAL CONDUCTIVITY (W/m · K ) TEMPERATURES OF MATERIALS ( °C): k skin =.37 T coal = 538 °C (1000 °F, 811 K) k coal =.1 T ash = 205 °C (400 °F, 478 K) k ash =.08 T foot,i = 32.2°C (90 °F, 305.2 K) k fat =.2 K air =.044 SURFACE AREA OF FOOT =.02 m 2 LENGTH OF MATERIAL (meters): DENSITY OF MATERIALS (kg/m3): L skin =.001 ρ fat ≈ 920 L coal =.01 ρ skin ≈ 1010 L ash =.02 ρ avg ≈ 965 L fat layer =.002 L air =.01 HEAT CAPACITY OF MATERIALS (J/kg ·K) c p,fat = 2973 c p,skin = 3662 c p,avg = 3318