Thursday, January 15, 2009


It is approximately as cold as a well-digger's hinder parts in January here in Indy -- and that's cold, since, you see, the temperature at the bottom of a well is pretty much the same year-round and old-fashioned wells took a degree of maintenance, so the well-digger was warm enough on the job, but when he climbed back up on a cold Winter's day, usually soaked the the waist, he was gonna be a lot colder than everyone else.

Where was I? Oh, yes, it's so cold now that if you spit out a second story window, it's turned into a an iceball on the way down and shatters when it hits -- and it's got to be awfully cold to tempt me to spit in public.

Naturally, I have been using those chemical handwarmers (and if you don't, you should: they're wonderful!). You pop a couple of 'em out of their air-tight packages, stuff 'em in the pockets of your second-layer garment, layer on over that and your core stays toasty warm. It's a huge help!

But how do they work? I fell to wondering what the end-product(s) of the exothermic reaction might be. Can you have a bunch of them warming your car? Could my friends who work on the big starships of the Hidden Frontier stuff 'em in their pressure suits when working in the colder holds? Yes, as happens, they could.[1] Chemical handwarmers work by rusting! More or less.

Ha ha, you say, that's a joke from High School Chemistry, all oxidation is "rusting." Nope, it ain't and yes, this is. Okay, they sneak in a catalyst to make it go faster and some other odds and ends to keep it from going too fast,[2] but the stuff that's doing the work is iron becoming iron oxide. Which is pretty nifty. Also nifty: you can stop and start the reaction. All it takes is a decent zip-lock bag: stick the handwarmer in it, squeeze out as much of the air as you can and zip it shut. Once the remaining oxygen is used up, it cools down and is ready for the next use. Since some versions will warm for ten hours, it's useful to be able to save that warmth for later. Funny, they don't so much mention that in the directions on the label.

These things are a must for a "just-in-case kit" for your car, or for a Winter bug-out bag. Made of win!
1. However, a version of the mechanical counter-pressure suit is the most common pressure suit, at least in Anglophone space, so there would be some details to work out to get oxygen to the warmers. I should ask -- the actual fix may be as simple as electrically-heated motorcycle oversuits, bought right off the rack. Plus, most parts of the starship, the problem's too much heat, not a lack of it.

2. The Data Viking is snickering as he reads this, remembering that I got through Chem class on glibness and last-minute memorization, whereas he showed a remarkable aptitude for the subject.


Robb Allen said...

When I was in the Marines, I had these hand warmers that were microwaveable (or you could boil them) and were reusable.

They had a small metal disc inside a package of clear gel. By popping the disc (similar to the die roller in the game Trouble), it would mechanically whack the gel which would cause a chain reaction. The gel would solidify, releasing heat as it went. It was good for about an hour or so.

Then, you reheated the gel via a microwave or hot water or whatever and the gel would 'melt'. Once it cooled off, it was ready to be activated again.

Came in real handy during morning PT sessions in the snow.

og said...

I have made my own handwarmers, the recipe is on the web somewhere. I prefer a jon-e-warmer, they get hotter and work longer- but for places where no open flame is acceptible the chemical ones are nice.

Turk Turon said...

Be careful using hand warmers in an all-oxygen atmosphere on your starship; they could turn into little thermite bombs. Melt right through the hull. Worse than molecular acid. Make good weapons, though.

loki said...

Be careful with everything in an all-oxygen atmosphere. I still remember burning steel wool in high school chemistry.

At any rate, be glad you're in Indy where it's warm. Here it's minus 15 (up from minus 17).

Joseph said...

I have used them a time or two to warm up a cold sleeping bag when camping.

Ritchie said...

I'm a little hesitant to mention this in an environment of techies and tinkerers, but..MRE heaters work on a similar principle, except you add water. Iron, water, what's left?? The directions do caution against using in enclosed spaces. Hydrogen, anyone?

Roberta X said...

Turk, a (US/Commonwealth) starship's atmosphere is not too especially different from that of the high Rockies in composition and pressure. This saves no end of fear and fiddlin' around. They used mixed gases from the start.

Robb's USMC handwarmers actually work by freezing! A super-cooled supersaturated solution, they'd normally be solid below room temps. Or so they tell me.