::A Geek in Korea::

Since students are always walking to their different academies in all sorts of weather, they have tricks to keep themselves warm. Back when I worked at a school that had inadequate heating, the students used to bring in chemical-reaction hand heaters to show off to their friends. They’d never, ever let me touch one, or explain to me how they worked. I thought they were neat, but never remembered what they were called, so I couldn’t find out where to buy them.

It turns out that the word in Korean is translated as “hand heater” (손난로) (soun-nallo) These are sold in the ubiquitous pencil shops in any apartment complex, and any place where children might go in winter to buy supplies. You can buy these reusable packs cheaply for 500 won each. I got caught in a late night snow earlier in the week and bought one while I waited for a bus.

There is a small flat metal disc suspended in a liquid in a thick sealed plastic bag. When the pack is “charged”, that is, in a liquid state, you trigger a chemical reaction by bending the metal disc inside slightly. The liquid crystalizes before your eyes, and you’ve got hand warming heat in 5-10 seconds. They last for fifteen to twenty minutes. I had my gloves on, but there was definitely considerable warmth going through the entire heater to my hands. I have very sensitive hands that ache in the winter. It was great to have a portable heater I could stow away in a pocket, and for 500 won it’s amazing to think it’s reusable!

I told my wife about my cleverness in buying such a convenient little tool to stay warm. She reacted really negatively. “It smells so bad! The plastic smells toxic! Ugh!” The heavy pouch does smell like foul plastic, but I don’t really go around smelling items I don’t need to, and I wasn’t planning on wearing it anywhere near my nose.

To “recharge” the chemical reaction, I had to wrap the bag in a cloth to prevent the bag from melting onto the pot, then put it in boiling water for five minutes. This turns to hard crystaline white pouch back into the clear plastic solution I originally saw in the pencil shop. If I went about fiddling with the metal I could trigger the chemical reaction again and have twenty more minutes of heat.

I’m guessing the students were paranoid about letting people see their hand heaters because they’d have to boil the heaters if someone set off the chemical reaction in class, and that would mean cold hands as they walked to their next school. I’m going to keep using my little heater when I’ve got to take a bus ride, or if I walk my dog before work on a particularly cold day. I’m kind of worried I’ll open my bag to find out I’ve accidentally crushed the metal catalyst and set it off by accident. I don’t know how many times the chain reaction can be triggered, but it’s fun to watch science at work.