Hi Guys, I was reading a book (fiction) the other day - to cut a long story short there was one scene where the main character puts his hand in a pan of boiling water. This scene takes place at the top of a mountain (where the water boils at lower temperatures due to lower atmospheric pressure) and the character removed his hand from the pan of boiling water to reveal he is unhurt - the natives are impressed!

I was wondering whether this is possible. Lets say the boiling point of water was 60 degrees at the top of this mountain (it's a BIG mountain) and the water in the pan was bubbling away at this temperature. Surely the water contained in skin cells would also boil away at 60 degrees while in this environment? This would mean that putting your hand in boiling water in a low pressure environment should be just as damaging as doing it at sea level.

If someone could shed some light on this I'd be very grateful. FD

First of all, there is a flaw in the story. Presumably the natives are familiar with the mountain and have been to the top of it before and have discovered the lowered boiling temperature themselves. Unless the author conveniently states that the natives have a custom that prohibits boiling water at the top of the mountain, it would seem that the natives would most likely look at the protagonist's demonstration, yawn and say, "Yeah ... so what?".

Putting that quibble aside, you do point out something to consider carefully. You are right that if water in a pan boils at 60 degrees under that pressure, so would the water in the cells of his hand. It would however take some time for the pressure in the cells to fall to the level of the air outside, after climbing up the mountain. But the pressure would drop sooner or later, and then the water in the cells of his entire body should boil away (regardless of whether he dipped his body in a pan of water or not). Does this imply damage to his cells? I do not imagine that inflammation and damage to his hand from dipping it in boiling water at sea level is due to dehydration of the cells. I imagine it is due mostly to the high temperatures involved, as you could see from touching a dry pan at 100 degrees. Basically, the high temperatures induce a lot of temperature-dependent chemical reactions to run amok. Thus, the boiling water at the top of the mountain, even if accompanied by the boiling off of water within his cells, is not going to do such inflammatory damage and blistering/scalding, since the water is at a mere 60 degrees. However, prolonged heating of the protagonist's hand to 60 degrees at that altitude should result in a dehydrated hand like an Egyptian mummy's sans bandages.

I overlooked possible damage by bursting of cells when their water boils into steam. For bursting to happen, several conditions must be met. First of all, the chemicals dissolved in the cell water must lower its boiling point at that pressure, or at least not raise it (or else the cell fluid will not boil at 60 degrees). Next, the rate of heat transfer into the cell across the delta temperature of (60-37) must be high enough to boil the cell water at a rate faster than the resulting steam can diffuse out of the cell walls. Presumably, this would happen, at least for the surface layers of his hand which are in closest contact with the boiling water. Finally, the elastic cell walls must be weak enough to rupture at not too high an internal steam pressure. (If the cells walls are too strong, then the internal pressure would rise sufficiently to suppress further boiling.) If all these conditions are met, the protagonist should be left with burst cells which are dried out, effectively killing off his hand or at least the surface layers of his hand. Incidentally, in the previous post, I have an error: the words "(regardless of whether he dipped his body in a pan of water or not)" should be struck out. His body would normally be at 37 degrees. He would need to dip his hand into 60 degree boiling water in order for the internal boiling to take place.

Thanks Ananda - that was a good response!

Incidently the book was rubbish. The whole hand in boiling water thing was a test to see if the local gods would allow the main character to live - if he could endure the pain he could go free. He asked to undergo the trial at the top of a holy mountain (so he could be closer to god - doh!). The book was bollocks - the physics is quite interesting though