Nope. In physics lab we would routinely play with liquid nitrogen. I’ve dunked my whole hand into a bottle of the stuff and pulled it out again, perhaps 2 seconds elapsed time, and came out with only a slight prickliness and no damage or freezing.
The heat from your body will temporarily create a boundary layer of nitrogen gas between you and the liquid nitrogen that insulates your skin. I’ve poured some into the palm of my hand, and have held a marble sized puddle for many seconds watching it boil and bubble until it completely evaporates.
Cool stuff.
However, it can still be very dangerous, so the usual disclaimers (know what the hell you are doing before doing it) apply.
Get your hand nice and wet, and you can dip it in molten lead, too - this time it’s water, not nitrogen, but again a layer of steam provides a brief period of insulation. I forget what the phenomenon is called.
Jearl Walker has been doing these demonstrations for decades, and has written supplementary essays for the much beloved (and sometimes loathed) Halliday & Resnick physics textbooks. He’s also a cautionary tale. Despite being a leading world expert in this kind of physics demonstration, he’s suffered serious burns, shattered teeth by contact with liquid nitrogen and had other serious mishaps.
I’ve done of his demos myself, but they’re definitely in the “Kids, don’t do this at home!” category.
Is it Bernoulli’s principle that states that the evaporation of sweat an/or moisture on the soles of the feet creates a slight cushion of vapor that lasts long enough for you to take the steps?
That, combined with not lollygagging across the coals, does it (seeing as that “protective layer” will disperse pretty quickly with time and pressure).
A side of beef would be an excellent model for the actual freezing of a human.
To bring the body of a (dead) 80 kg soldier from 37°C to 0°C, you’d need to extract roughly 3000 kcal (80kg * 37°C). To actually freeze the body once it was ay 0°C would require removing an additional 6500 kcal.
By contrast, a fit 80kg soldier (live, resting) might burn 2000-2500 kcal per day. Since immersion in arctic waters overwhelms the body’s self-heating response (shutting it down), and can even kill in as little as 5-10 minutes (per S&R data), I think allowing 100 kcal (one hour’s basalk metabolism) for biogenic heat is generous. The body has several mechanisms to allow it to generate several times its normal heat, but few of them could be mobilized in a “sudden freezing” scenario. Peri-renal “brown fat” pads, for example, wouldn’t have time to kick in, and even shivering takes minutes to achieve peak heat output. Clearly, metabolic heat is a tiny fraction of the heat required to cool and freeze the physical body.
I treated the body as 80kg of water.to get an order of magnitude estimate. To accounts for dissolved chemicals, bone, fat, the fact that human flesh has a substantially lower freezing point than pure water, etc. a side of beef would serve, though of course, a whole 80kg carcass (e.g. a small shorn sheep or pig) would be more accurate. (Though biological organisms don’t have a “freezing point”. Some fatty tissues are soft at body temperature but firm or hard at room temperature, Other tissues won’t freeze until -10°C or less. The freezing point of bone -a major part of the body by mass- is a problematic technical question]
Here’s a site that outlines the calculations for blast freezing various kinds of meat for food distribution. It makes it pretty clear that the freezing time would be on the order of hours, not minutes or seconds, by air-cooling at -25°C (-13°F). Air has a very low density, and hence a low heat capacity, so liquid or solid contact freezing would be faster. This site has calculations for plate contact freezers, and again, it appears that the freezing time would be on the order of hours, not minutes or seconds. (note that the endpoint core temperature of “frozen fish” can be quite high compared to surface temperature. The fish is considered ‘frozen’ because it will equilibrate by itself over time; this may not fit your definition, however