Skip to Navigation
University of Pittsburgh
Print This Page Print this pages

November 21, 1996


Help Wanted: University mathematician needed to develop a computer model of a foot engaged in fire-walking based on the laws of thermodynamics. The purpose of the project is to predict the temperature that the flesh of the foot reaches as a function of time.

No salary. No tenure. No fringe benefits, except an opportunity to join the ranks of mystics, circus performers and New Age gurus by walking unharmed across a bed of red hot coals.

"It doesn't strike me as a particularly difficult task for a mathematician," says Dave Willey, a physics instructor at Pitt's Johnstown campus (UPJ). "I just don't have the time myself or the background to just quickly whip it out. That's why I'd like to get some help." Willey wants to develop a computer model of a foot engaged in fire-walking because he has been using the ancient ritual, or at least a video of him doing it, to teach the laws of thermodynamics. UPJ's 1990 Teacher of the Year in Natural Sciences believes in "jump starting" his lectures with such feats.

To demonstrate heat, for instance, Willey has been known to pour a pint of liquid nitrogen into a two-liter soda pop bottle, cover it with a plastic 50-gallon garbage can and stand back while the nitrogen thaws into a gas, expands and causes the bottle to explode, sending the garbage can rocketing 50 feet into the air.

For a lesson on electricity, he has used a Van de Graaf generator to show how like charges repel by making a stack of aluminum plates float off the instrument one at a time. And for a class in energy and pressure, he has lain on a bed of nails while a concrete block is broken on his chest.

In fact, Willey has developed an entire physics demonstration program called "How Does a Thing Like That Work?" Backed by an Eisenhower Grant, he has presented his program at high schools in the Johnstown area, as well as at a meeting of the Association of Physics Teachers.

While all of Willey's experiments are interesting and fun ways to learn physics, none of them quite captures the student's attention like walking barefoot on red hot coals, which he uses to illustrate the difference between temperature and heat. "Just because something is up at a high temperature, doesn't mean that it has a lot of heat to give out," he explains.

One way heat is transmitted is through conduction that occurs when two things touch, he explains. Conduction happens when energetic molecules (the hot coals) that are vibrating collide with more sedate molecules (the soles of the feet) and transfer their energy to them. The thermal conductivity of coarse charcoal is very small and that of flesh only about four times greater, so the coals do not have a lot of heat to give out. By comparison, the thermal conductivity of most metals is several thousand times that of wood coals or flesh.

To illustrate what he means, Willey points to a pan in an oven. Even though the air around the pan is the same temperature as the pan, a person using a pot holder can remove a pan from an oven without burning exposed flesh because air, unlike the metal pan, is not a good conductor of heat.

A native of England, Willey, 49, joined the UPJ faculty in 1975. He became interested in fire-walking as a teaching tool after reading "Fire-Walking As a Lesson in Physics" by University of Colorado physicist John R. Taylor in the March 1989 issue of The Physics Teacher.

After reading the article, Willey remembered his mother picking up hot wood coals that had fallen out of the fireplace and tossing them back without getting burned. He knew from her example that he would not get burned fire-walking, but he was still hesitant when it came to actually stepping on a pile of hot coals in his backyard.

"The very first time I tried to do it, my foot went to the side of the fire," Willey says. "My body just went, 'No way, Dave!' The second time I made a much more conscious effort, put my foot on it [the fire], stepped across it, took my foot off it and went, 'Oh, I am fine.'" Having passed the test on a small pile of hot coals, Willey then elected to try a full-fledged fire-walk on a 12-foot bed of coals built up on a neighbor's farm. The UPJ administration will not allow Willey to fire-walk on campus because of concerns about fire and liability insurance. "Right up until the moment when I was about to walk along it, I was feeling pretty good," Willey says. "But when we raked it out, boy, it really felt hot and I started feeling a little dubious." Summoning up his courage, Willey took one step across the pile and found his foot was fine. Then he put his hand on the pile and found that nothing happened. Finally, he made the walk. Willey has repeated that walk about two dozen times on three different occasions. His most recent walk was a few weeks ago. Photographs from it are slated to be used in the new edition of the textbook "Conceptual Physics" by Paul Hewitt.

Fire-walking as a ritual has been practiced by people from all parts of the world for thousands of years, according to Willey. The first written reference to fire-walking appears in a story from India dating back to 1200 B.C. Since then, it has been observed and recorded as an organized event in numerous cultures and religions.

Although it continues to be looked upon by some people as a paranormal activity, it has been fairly well understood and explained using the principles of physics since the 1930s.

In 1935, the University of London's Council for Physical Research organized a fire-walk to study the phenomena scientifically. In that experiment, three people walked across a 12-foot pit packed with mainly oak embers measured at 800 degrees Fahrenheit.

Two years later, in April 1937, the council organized a second fire-walk. Three of the participants in that experiment walked away without so much as warm feet, while the others received only a few very minor blisters.

Following those 1937 experiments, the council issued a report stating that neither religious faith, nor supernatural powers had anything to do with the performance of the feat. Instead, they concluded, the secret of fire-walking lies in the low thermal conductivity of the burning wood and the short time of contact between the hot coals and the feet.

After the Council of Physical Research's experiments, fire-walking was basically forgotten in the West until the early 1980s, when businesses promoting self-esteem made the activity a part of their programs. Many of those businesses still exist and most of the operators tend to portray fire-walking as something in the "mind-over-matter" realm instead of a fact of physics.

According to Willey, several facts need to be considered to understand how walking on a bed of red hot coals is possible without sustaining injury. The first fact is that hardwood and charcoal are good thermal insulators. The use of wood on the handles of such things as skillets and soldering irons is a good indication of wood's insulating properties. Wood is just as good an insulator when on fire, according to Willey. And charcoal is almost four times better an insulator than dry hardwood. Another important factor to consider is the length of time that the sole of the foot is in contact with the coals. Willey says it is neither necessary nor advisable to run when fire-walking because it could lead to a fall. A brisk walk is the best approach, with each step taking less than a half second. During a 14-foot fire-walk, each foot is in contact with the coals for only a couple of seconds.

A small group of people in the state of Washington have reportedly made fire-walks of 120 feet, but Willey finds that doubtful because it would require the feet to be in conduct with the coals for several seconds. He says he has seen a film of the walk and it appears as if the coals have been raked to both sides, creating a path down the center. Willey also is suspicious because members of the group maintain that they are able to stand in the middle of a bed of coals for 30 seconds to a minute and handle the coals for similar periods of time. One group member even claims to be able to fire-walk on red hot steel, which Willey does not believe at all.

"What I am hoping is that next year I can use my faculty development money to buy air tickets and go out there and see them do one of these long walks and actually take some measurements and take some video and see what's going on," he says.

Humans cannot walk barefoot on red hot steel, according to Willey, because it is a thousand times better conductor of heat than wood coals. Although Willey himself has never been burnt, a few of the roughly one dozen people who have tried fire-walking with him have sustained minor blisters. Willey says the blisters were the result of those people being so elated by walking on hot coals that they forgot to step in the pool of water he keeps at the end of the coal bed.

"If you get stuff stuck to your feet, especially if hot coals get pushed up between you toes, then the time of contact gets to be real long and then you're going to get burned," he says. "The pool of water is so that everything is over after a few seconds." For other physics instructors who would like to use fire-walking or some of his other experiments in their classroom, Willey has posted information about them on his Internet page. The address is

Willey has created a video, "Firewalking-Myth vs. Physics," in which he demonstrates fire-walking and explains the relevant physics. It is available for $59 from Hawkhill Associates, 125 E. Gillman St., P.O. Box 1029, Madison, WI 53701-1029. Phone 1-800-422-4295.

And what do Willey's students think of it all? "They just think it's me being crazy as usual. They're kind of used to me doing strange demonstrations."

–Mike Sajna

Filed under: Feature,Volume 29 Issue 7

Leave a Reply