Firewalking is Just Physics, Not Mysticism
Posted by mattusmaximus on July 28, 2011
Fire is cool… well, not cool, because it’s actually pretty damned hot. But what I mean is fire is really interesting to watch – what kid hasn’t at some point been fascinated simply staring into the depths of a campfire? Do you know what’s more interesting?… the fact that some people actually like to walk on fire. This in and of itself is just all-around awesome, but then some woo-meisters have to go and spoil it with a bunch of made-up New Age nonsense. The purpose of this blog post is to show you why firewalking really works.
My skeptical physics colleague David Willey shows his stuff, sacrificing himself for science. **THIS IS EXTREMELY DANGEROUS AND SHOULD NOT BE PERFORMED WITHOUT PROPER SUPERVISION**
And just to show you that I put my money where my mouth is, below is a video shot of me and my colleagues performing an experimental firewalk back in the summer of 1999…
We decided that we wanted to study the physics of firewalking for ourselves and made this video as a way of documenting the effect. There are (were) two basic competing, scientifically plausible ideas for why it is that firewalkers are not too damaged by the high temperatures during the walk across hot coals: low thermal conductivity and the Leidenfrost effect.
In the first hypothesis, it is the low thermal conductivity of ash, wooden coals, charcoal, or rocks that the firewalker traverses in their journey. Even though the temperatures are extremely high (on the order of 500-800 degrees Fahrenheit), the low thermal conductivity means the rate at which heat will transfer from the hot material to the walker’s feet is very slow. This is why when you check out a baking cake in the oven it is okay to touch the batter but not the metallic pan – the thermal conductivity of the cake batter is low whereas that of the metal pan is very high!
In the second hypothesis, the Leidenfrost effect protects the walker’s feet. The Leidenfrost effect is the same thing that prevents your finger from being burned when you touch a hot iron with a wet finger. The hot iron turns the spit into steam which forms a temporary insulating layer between the iron and the finger. In this argument, the sweat on the walker’s feet is what is vaporized and then protects the feet from the hot coals.
In the video we tested out these two ideas, and we found the Leidenfrost effect to be inadequate to explain the phenomenon. It is the low thermal conductivity of the coals which prevented our feet from being too damaged – I walked a total of four times, three times dry and once with very wet feet. After three dry walks my feet were fine, with only one very small blister (half the size of a pinky nail, barely visible on the video) on one foot, but during the walk with wet feet, to test out the Leidenfrost effect, I found the coals sticking to my feet… OUCH!!! That is where I got badly burned (which is apparent by the very end of the video).
One thing we found was clear: we successfully negotiated the fire bed without any appeals to New Age mysticism or supernaturalism – no prayers were muttered, no crystals stroked, and we never even bothered to measure our “chi” levels. Such appeals to woo are simply not necessary to explain what is happening here – in fact, I have a challenge: if any New Age firewalking guru wants to really convince me that they have paranormal powers, then they’ll walk barefoot across red hot METAL!
I submit that no one will ever seriously attempt such a stupid feat, and even if they did I guarantee they’ll only do it once 😉
For more information on the physics of firewalking, I suggest reading Dr. David Willey’s page at http://www.pitt.edu/~dwilley/Fire/FireTxt/fire.html