Friday, February 4, 2022

Cooking with Hexamine

Not actually Erin.
& is used with permission.

Having tested the Firebox Nano with both wooden sticks and an alcohol burner, I decided to go for the Hat Trick by testing a hexamine fuel tablet on it as well. For those who are unfamiliar with the term, a "hex tab" is the kind of solid fuel which comes with a lot of pocket stoves, such as the Esbit

Hex tabs are interesting in that they will last effectively forever if they are kept dry. To that end, most hex tabs I've seen have come individually packaged in a plastic blister with a foil seal. The one I used for this review was bought circa 2009 and has been bumping around various bags and packs of mine. 

Please be aware that hex tabs work through by converting hexamine into formaldehyde, which is toxic to ingest. If you use hex tabs, be sure to wash your fingers after handling them, and of course you don't want to breathe the fumes -- but then, you don't want to breathe the smoke from a burning wood fire or the fumes from burning denatured alcohol. (Really, just don't breathe fumes in general.) If you're concerned about health effects then cover any cup, pot or pan you use for cooking over a hex tab, and don't do thinks like roast hot dogs or marshmallows over the open flames, and you ought to be fine. 

If you wish to know more about hexamine, here is the material science data sheet (MSDS) for it. 

Hex tab on the Firebox Nano fuel plate

Again, the tests are: 
  1. How easy is it to light and keep fed.
  2. How quickly it will bring 16 ounces of water to boil in a steel mug. 
  3. How quickly it will bring 24 ounces of water to boil in an uncovered aluminum pot.
  4. How quickly it will cook a single egg on an aluminum skillet. 

Test 1: Fire Starting
I'm aware that hex tabs can be difficult to light with a spark, but this is the first time I've had trouble lighting something by applying a direct flame to it using a disposable Bic lighter. While I suppose I could have just applied continuous flame until success, I felt this would be a suboptimal approach in a survival situation where it might be critical to conserve lighter fluid. Instead, I made use of my crazy idea and applied a thin layer of sterno to the top of the hex tab, which caught instantly and caused a near-immediate ignition of the hex tab (it turns brown as it burns). In hindsight I probably applied too much, and a single dab of sterno would probably have worked just as well. 

Once lit, the hex tab stayed lit and burned evenly and consistently, needing no further attention from me. 

Test 2: Cup Boil
Once I knew the tab was burning I placed my steep cup with 16 ounces of water on the Nano stove. The water came to a rolling boil after about 8.5 minutes. 

Test 3: Pot Boil
It was obvious to me even before the water boiled that the hex tab had burned at least halfway through, so I filled my pot with 24 ounces of water in advance and had it sitting by the stove. Once the cup of water was boiling, I removed it and immediately replaced it with the pot. 

Unfortunately, I was correct in my estimate. 3 minutes into the test the tablet was not producing enough flame to reach the pot, and by 4:30 it was completely consumed. This gave the tab a total run time of approximately 13 minutes. 

The last moments of a hex tab: burning, but not cooking. 

I tested the water when the tab died, and it was the temperature of a pleasantly warm bath but nowhere near boiling. A steel cup and an aluminum pot have different levels of conductivity, so while I could say "16 ounces boiled in 8:30, which means 8 ounces should take 4:25 and therefore 24 ounces could boil in 12:55," I do not have enough confidence in that statement to stand behind it. 

I chose not to expend another hex tab to complete test 3 and 4, as I felt that I learned what I needed to learn, specifically that a hex tablet does not burn long enough for multiple cooking operations. I might have been able to cook an egg after boiling 16 oz of water, but I wouldn't want to make that gamble in a survival situation. 

Side-Note: Residue
The residue left behind by a burned hex tab is interesting. What remained on my burn plate was a hard, almost resin-like substance that must be scraped off with a metal tool. 

Conversely, the residue left on the bottom of my steel cup and aluminum pot, while funky-looking, came off easily with a green Scotch-Brite pad and some dishwashing soap. 

My Rating: B
Hexamine tablets have a place in a prepper's kit, but they have limitations which makes them less than ideal:
  • They are somewhat bulky: 1" high by 1" inch wide by 2" long. 
  • They have a limited runtime. 
  • Their heat output cannot be moderated. There is no way to simmer; there is only "on" and "off". 
  • Once they have been burned they become fragile. Picking it up and storing it for later use would be awkward, but throwing away an unused portion is wasteful. 
With that said, the tablets are lightweight, store indefinitely, burn dependably, and appear to have the same performance -- albeit a much shorter run time -- as an alcohol stove

I would pack a few hex tabs in a BOB or GHB for emergency use, but I would not make them my main fuel source. 

1 comment:

  1. Brings back memories of my steam engine that I had as a kid. It used the tables to heat the boiler.


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