The Straight Dope | The Straight Dope | Chicago Reader

The Straight Dope 

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? --Ed Dolnick, Chevy Chase, Maryland

Cecil initially feared he was going to have to sacrifice his tootsies 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 fool journalists have rushed in where more rational people would just as soon not tread. Fire-walk therapy, God help us, is widespread these days.

There's some disagreement on why fire walking works, but this much is clear: it does work. There's no trickery involved, although modern fire-walk 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.

Why don't 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." This is 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. As a precaution, sometimes you're directed to walk over a moist surface such as grass before stepping out on the coals. (Another trick is not to replenish the coals; they quickly cool.)

(2) Not enough heat. This one requires some thought. While glowing coals have a high temperature (typically 600 degrees Celsius), they don't contain all that much heat. (To use a water analogy, you've got a lot of pressure but not much volume.) What's more, the coals typically used 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 that's 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 has not only walked on hot coals (though he gave it up after getting badly burned once--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. Just don't volunteer in Jearl's class when he asks someone to give him a hand.

Art accompanying story in printed newspaper (not available in this archive): illustration/Slug Signorino.

Support Independent Chicago Journalism: Join the Reader Revolution

We speak Chicago to Chicagoans, but we couldn’t do it without your help. Every dollar you give helps us continue to explore and report on the diverse happenings of our city. Our reporters scour Chicago in search of what’s new, what’s now, and what’s next. Stay connected to our city’s pulse by joining the Reader Revolution.

Are you in?

  Reader Revolutionary $35/month →  
  Rabble Rouser $25/month →  
  Reader Radical $15/month →  
  Reader Rebel  $5/month  → 

Not ready to commit? Send us what you can!

 One-time donation  → 

Popular Stories