A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Can you walk on hot coals in bare feet and not get burned?

June 14, 1991

Dear Cecil:

My friend Heather and her hubby just laid out some fairly big bucks to spend a weekend learning how to maximize their total personhood and all that. Highlight of the weekend was a scamper across hot coals. The idea was to impress you with the power of your mind — if you kept thoughts of cool moss in mind as you walked, your feet wouldn't burn. The coals were in a strip about a yard wide and ten feet long. Walkers, in bare feet, made it through with few problems. Heather made it too, with no trouble and no sign of damage to her feet.

Heather's (and my) question is this: she believes that, via mind over matter or hypnosis, a person might lower his blood pressure or speed up his pulse or even will himself not to feel pain. But whether she felt it or not, shouldn't the coals have burned her feet? After all, if you throw a steak on the grill, it cooks regardless of the thoughts it happens to be entertaining.

What's the deal? Does psychology triumph over physics? Is it a con — aren't the coals hot? Do sweaty feet protect you with a layer of sizzle?

Cecil replies:

Cecil initially feared he was going to have to risk cherished portions of his being for the sake of the Teeming Millions (and what have you guys done for me lately?). Fortunately, a quick check of the Straight Dope's vast data resources reveals that lots of journalists have rushed in where more sensible people dared not tread. Firewalk therapy, God help us, is widespread these days.

There's some disagreement on why firewalking works, but this much is clear: it does work. There's no trickery involved, although modern firewalk entrepreneurs do take a few precautions, about which more below. Mind over matter has nothing to do with it. Skeptics have tried it with no preparation whatsoever, or (worse) while murmuring "hot rocks, hot rocks." They got over just fine. There's not much margin for error, though. Blisters are fairly common and a few people have been badly burned.

What protects the rest? Two phenomena get the credit:

(1) The sizzle effect, also known as the Leidenfrost effect: a thin layer of sweat protects you. As Peter Garrison put it in a 1985 article on the subject in Omni magazine, "a liquid exposed to intense heat will instantaneously form an insulating boundary layer of steam." That's what enables you to snuff a candle flame painlessly with your fingertips after you've moistened them with spit. The soles of the feet are well supplied with sweat glands, and Lord knows I'd perspire while waiting to hike through hell. In addition, sometimes you're directed to walk over a moist surface such as grass before stepping out on the coals. (Another trick: don't replenish the coals; they quickly cool.)

(2) Not enough heat. This one requires some thought. While glowing coals are plenty hot (typically 600 degrees Celsius), they don't contain all that much heat — that is, thermal energy. (To use a water analogy, you've got a lot of pressure but not much volume.) What's more, the coals aren't charcoal but rather ordinary wood, which is a poor conductor. When you walk on them, your feet absorb the surface layer of heat, but there's too little of it to burn you. Fresh heat from within the coals makes it to the surface too slowly to do you any damage.

But fire-walking in some parking lot is for wimps. If you're hard core there are more challenging methods. I've just spoken to my bud Jearl Walker, the former Scientific American columnist and, it turns out, the G. Gordon Liddy of physics.

As a classroom demo of the Leidenfrost effect, Jearl not only walked on hot coals (he gave it up after getting badly burned onc — he was so cool his feet didn't get sufficiently damp), he also dips his bare hand in water and then plunges it momentarily into a vat of molten lead, 700 degrees Celsius. Says Jearl, who's even done this on Johnny Carson, "there is no classroom demonstration so riveting as one in which the teacher may die." It'd definitely penetrate my ennui, I'll tell you. Just don't volunteer in Jearl's class when he asks someone to give him a hand.

More on firewalking

Dear Cecil:

A friend of mine forwarded your column on firewalking to me. It was a good column, but as you'll see from the enclosed journal article, which I co-authored, the sizzle effect is not critical (and Jearl Walker agrees with me, but keeps forgetting).

Cecil replies:

Bernie's article comes down foursquare behind the not-enough-heat theory and says in addition that the firewalker's feet may be insulated by dirt, calluses or water. Bernie discounts the Leidenfrost effect, noting that a firewalker with a pair of rope-sole sandals gamboled through the coals without damage to the sandals. Since the ground was dry, the day was cold, and sandals don't sweat, there was no moisture, which is the key to the Leidenfrost effect. The sandals' survival therefore must be credited to something else.

I am pleased to set the record straight, naturally, and hope I have not seriously retarded the advance of science in the meantime. However, any time you've got a phenomenon that lets you work in a Jearl-Walker-tempts-death story, as was the case with the Leidenfrost effect, in my book you want to cut it a little slack.

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