This wasn't a random fact off the top of my head. We're doing Search and Rescue training this month, and I attended a four-hour training session on Monday night. The point was about setting priorities if you happen to be the first person to come upon someone, wounded or hypothermic or alone in the wilderness. People tend to think about food in survival situations, but you can survive without food for a long time. Water? Days. But you can die of exposure in less than a day, as our musical guest explains.
Our instructor is a man I greatly like. He's some kind of old Army, though he hasn't copped to it exactly; post-Nam Ranger, I'd guess. In his sixties he still BASE jumps and does SCUBA diving into caves. He's an old hillbilly who hates cities and has every kind of Deplorable instinct, another old Southern Democrat like me.
And just now and then, amidst his long discourse on all these topics, he'll depart into extraordinary explanations that quote physics formulas from memory and then explain how they apply to survival situations. Somebody asked him about those Mylar 'space blankets' they sell. Shouldn't we carry them to wrap up hypothermia victims so they'll warm? Nope, it turns out: his account of why they're useless in those cases was one of the most erudite things I've ever heard, coming from a guy you'd probably have thought a backwoods redneck if you didn't stop and listen to him talk for a long while.
Here's the formula, by the way. The example is of the surface of the moon, but this is physics, so it applies to the hypothermic guy who fell in a mountain creek with exactly equal force.
Next week is orienteering, which I think I know how to do. I learned it many years ago and have done quite a bit of it, but I won't be surprised if I understand it better after he's done teaching us.
6 comments:
The best first-aid advice I know for someone too out of it to drink anything warm, and already too cold to benefit simply from getting dry and inside good blankets. Do get him dry and out of the wind, then ASAP apply warm, dry compresses to the neck, chest wall, or groin. Don't apply them to the arms or legs: the extremities can tolerate cold better than the core or the brain. It's possible that the only warm, dry compress available will be your own body.
Someone who's still coherent is not too bad. Shivering is a sign that things are going south, but still not too bad. If someone stops shivering, gets stupid, or even worse loses consciousness, things are critical.
About orienteering, I have no expertise, never having been left or lost in the wilderness. I do wonder about fictional characters, or acquaintances, who can completely lose track of direction on a cloudless and even moonlit night. Do they have any idea where the constellations are, or where the sun and moon rise and set? The weather would have to be pretty bad, or the canopy pretty dense, to obscure all the clues for long. I'm a city girl, and I can get disoriented when the sun is high, but sunrise and sunset are pretty strong markers.
I'm thinking particularly of the movie "The Bear," in which our hero goes down in a plane crash in remote Alaska. There's an inspiring scene in which he MacGyvers up a compass from a bit of iron floating in something or other, but he seems oblivious to the sunrise and sunset.
"Real materials emit energy at a fraction—called the emissivity—of black-body energy levels."
Black bodies emit (and absorb) radiant energy most efficiently. The more reflective the surface, the worse it is at emitting.
My own thinking--such as it is--on Mylar blankets has been that they're fairly adequate at blocking the flow of heat. That would make them OK for a normally warm person to wrap himself in to stay warm for a while by holding in his body heat, but decidedly counterproductive for wrapping a hyperthermic person in since the Mylar would block heat from getting to the cold body from the outside.
Regarding warm compresses applied to the neck of a hyperthermic person, the advice I've seen is to do that to the inside of joints, where the arteries are relatively near the surface, but don't do it to the neck. Warming the brain too quickly can cause damage.
Eric Hines
I think I should have made the conclusion explicit. Mylar by itself is not exactly great at reducing heat loss via conduction, but is quite good at reducing heat loss via radiation.
James, that's right. Also, once you're applying heat, putting the mylar over the victim *and* the heat source together can help direct the heat to the victim more efficiently.
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