Firewalking is the act of walking barefoot over a bed of hot coals. Since 1200 BCE, firewalking has been used in ceremonies of healing, initiation, and faith. It has gained a contemporary following among modern motivational speakers and self-help gurus.

Loring Danforth, Ph.D., Firewalking and Religious Healing (1989), Princeton University Press.

Why it Works

As two bodies of different temperatures come together their temperatures will trend toward a state of equilibrium. That is, the hotter body will lose heat while the cooler body will gain heat.  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 bodies in question here are human feet (which mainly consist of water) and burning coals.

What prevents burning?

Water has a very high specific heat capacity when compared to coals.  The temperature of the foot changes less than the temperature of the coals.  Water also has a high thermal conductivity, and on top of that, the blood in the foot will carry away the heat and spread it throughout the body.  Charcoal has a very poor thermal conductivity, so the hotter body consists only of the parts of the coal which is close to the foot.  The coal cools down, its temperature sinks below the flash point, so it stops burning and no new heat is generated.

Michael Shermer of Skeptic Magazine investigates fire-walking.