The following is from a video released in 1994 about firewalking by David Willey who has walked on fire several times.
Firewalking has been practiced for thousands of years by people from all parts of the world. The earliest known reference to it is an Indian story, from about 1200 B.C. Since then it has been observed as an organized event in many different cultures and religions. Although it was, and still is by some, thought to be a paranormal phenomena, it has actually been fairly well understood, and has been explained using the principles of Physics for at least the last half century.
In the 1930's the University of London Council for Psychical Research organized two firewalks to study the phenomena scientifically. In 1935 an Indian, Kuda Bux, and two British scientists walked across a 12 foot fire pit, containing mainly oak embers at about 800 degrees Fahrenheit. Then, in April of 1937, another firewalk was performed for the Council, this time by a Moslem man, Ahmed Hussain, an Englishman, Reginald Adcock, and several others. Neither Kuda Bux, Hussain nor Adcock were burned at all, and the others received minor blisters at worst. Pursuant to these events the council issued reports stating that neither religious faith, nor supernatural powers had anything to do with the performance of the feat, and then went on to conclude that the secret of the firewalk lies in the low thermal conductivity of the burning wood and that the time of contact between the hot coals and feet is short.
After that there was not much attention paid to firewalking in Great Britain nor America until the early 1980s. At about the turn of the decade there was a resurgence of interest due to lucrative businesses promoting self-image and confidence boosting courses which relied heavily on people firewalking as part of the course; many of them are still in existence. Most of those making money from these ventures tend to portray firewalking as something in the realm of "mind over matter" and not something understandable in terms of simple Physics. There are others though who are skeptical and do not believe that it requires a particular state of mind, or that anything extraordinary, in the true sense of the word, is involved.
Bernard J. Leikand and William J. McCarthy published a paper in the Skeptical Inquirer of Fall 1985, in which they asserted that firewalking is possible because of the low thermal capacity of the coals, as well as the short time of contact that the firewalker's soles have with the coals.
There are several features to consider if we wish to understand how walking on a bed of red hot embers is possible, without sustaining injury. Consider that both hardwood and charcoal are good thermal insulators. Wood was used on the handles of such things as saucepans and soldering irons to insulate them, before the advent of heat resistant plastics. Wood is just as good an insulator even when on fire, and charcoal is almost four times better as an insulator than is dry hardwood. Further, the ash that is left after the charcoal has burnt is just as poor a conductor as was the hardwood or charcoal, and is itself producing no further heat.
Another important factor to be considered is the length of time that the sole of each foot is in contact with the coals. It is neither necessary nor advisable to run, a brisk walk is reported to work best, with each step taking half a second or less. During a fourteen foot firewalk then, each foot will be in contact for a total time of a second or so. (The 120 foot walk done by Sara Raintree and Jim Jarvis, and reports of longer walks and people remaining stationary for extended periods on the coals are currently under investigation by the author.)
Heat can be transmitted in basically three ways, convection, radiation and conduction.
Convection occurs only in gases or liquids, i.e. fluids, when the cooler and hence denser portions of a fluid displace the less dense, warmer portions. It is where the expression "hot air rises" comes from, but convection is not that relevant to firewalking, because there are not any gases nor liquids significantly involved.
Heat can be transmitted by radiation as an electromagnetic wave, this is how heat reaches us from the sun. One's face is particularly sensitive to this radiation and that is why when you stand next to a fire you quickly get the sensation that the coals are very hot, however radiation does not transmit much energy to the feet during a typical firewalk, because of the relatively short length of time the firewalk takes. If there is a layer of ash on the coals, then this effectivly blocks the radiation from the foot.
Heat is also transmitted by conduction when two things touch and this form of transmission is the most relevant to firewalking because it is the soles of the walker's feet that come in contact with the hot coals. Conduction happens when energetic molecules, the hot coals, that are vibrating collide with more sedate molecules, the soles of the feet, thereby transferring energy to them, but the thermal conductivity of coarse charcoal is very small and that of skin or flesh is only about four times more. By comparison the thermal conductivity of most metals is several thousand times larger, metals conduct heat well, but non-metals such as charcoal or skin do not. Additionally, not all of the foot is in contact the whole time, because of the coarseness of the charcoal and how the foot is placed when walking. The foots arch seems to be where most people blister other than between the toes.
How does this relate to the possibility of injury during a firewalk? It is true that what temperature the flesh becomes will decide whether any injury is suffered or not, but it will be the amount of heat that is transferred from the coals to the feet that will directly influence that. What temperature the coals are at will be only one of the several factors that will influence how much heat is transferred and by how much the temperature of the soles will consequently rise. So, what I believe happens when one walks on fire is that on each step the foot absorbs relatively little heat from the embers that are cooled, because they are poor conductors, that do not have much internal energy to transmit as heat, and further that the layer of cooled charcoal between the foot and the rest of the hot embers insulates them from the coal's.
Having the bottoms of the feet wet might help absorb some of the heat given off by the coals, but I'm more concerned that no coals stick to my feet. In case they do, we place a water soaked carpet remnant at the end of the walk. The soles of my feet are fairly soft and I dry them immediately before a firewalk. The Leidenfrost effect does not seem to be involved during firewalking; even Jearl Walker says he is of that opinion these days, although he at first thought otherwise.
It would seem then, that a firewalk of short length is something any physically fit person could do and that it does not need a particular state of mind. Rather, it is the short time of contact and the low thermal capacity and conductivity of the coals that is important, and it is not necessary for the feet to be moist nor callused, although either may be of slight benefit. Longer walks appear to be possible if a layer of insulating ash is allowed to build up on a well packed down bed, where the temperature has been allowed to fall significantly from what it was when the coals were at their hottest.
This is not to deny that one may feel empowered by having walked on fire, nor is it to dispute that it may improve self confidence. I do however believe that firewalking is understandable in terms of basic Physics and is not supernatural nor paranormal.
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