Bad Luck With the FRH's... and ???'s

[rattattoo]

I took along some MRE's on a canoe-camping trip to Flagstaff Lake [further upstate here in Maine] this weekend. I wanted to show my buddy how they work and that they weren't really as bad as he might have heard.
The meals were mil-spec, 2006 dated, Enchilada dinners. Neither of the FRH's from those came to a decent heat. Neither did the two undated ones out of my collection of loose stuff that I had brought along for Sunday breakfast.

Is there anyway to tell whether an FRH is still usable?
What happens with them if they are accidentally under-filled or over-filled?
I thought I got the water quantity about right both times, but none of the heaters ever came up to the point of hearing the "sizzle". This despite the fact that they had been stuffed into those insulated pouches that I made up. Slightly warm, but certainly not "hot".

Will the FRH bags hold up if you simply pour in some boiling water before the end? Or can they overheat and fall apart?

I can certainly see why so many people are fans of the traditional kidney-shaped canteen cup for boiling the pouches. Even one or two bags would be cramped in my 1L cylindrical pot.
Does vendor make the canteen cup in aluminum so that it would be lighter in weight?

Thoughts?

[Name_not_found]

FRH, (the military ones, not civilian ones that need salt water) are just big hand warmers.

They are filled with iron filings and salt. When exposed to moisture (65% RH usually) they "activate" and begin to consume o2 (no o2 no water)

As to the water issue
Its a chemistry problem, X mols of iron can consume x mols of 02 before it finishes. Because you start with a finite amount of iron, you need to balance the speed of the reaction to get useful heat.

-Too much water and you will get more heat than normal but it wont last long enough to heat your food.

-Too little and it wont be fast enough to heat the meal reasonably (like a candle cooking a roast)

-Just the right amount of water means you get the right amount of heat for the right amount of time.

All that said, o2 sneaks in slowly over time unless sealed in something else, like the original outer bag, but even then its a slow degradation of quality over time.

[rationtin440]

I'm sorry that happened to you N_n_f. Unfortunately I have had no real experience with the FRH to share with you. I was fortunate enough to be on an ambulance crew during my national guard service, and our vehicle crew chief always had a small campstove for the 3 of us to heat MREs with "make sure you use it outside the vehicle!!" (the ambulance/evac section in my unit was famous for having the most-used canteen cups and messkits! ). I was wondering if you have had any experience with the German or British folding hexamine or esbit stoves. I have had good experiences with them and have heard many bad reports about the FRH, whether from MREs in current production or back when they were first introduced.

[housil]

FRHs also get old and loose some of their "power" due to my own experience. I´m still current eating 2003 MREs and their FRH are still "OK", but I also had plenty of duds they became only lukewarm.

This is why I only use (old) FRHs when any other way is not possible.

[RockyRaab]

I believe that the FRH passes its "use by" date faster than the food does. Your 8-yo units are quite a bit past the five-year mark where they seem to start "dudding."

There's nothing you can do to bring them back to life.

[Horsesoldier]

I never really made a study of them while still in uniform, but the idea they get out of date faster than MRE contents seems right, or there were some bad batches of FRHs that came down the pipeline. I remember one FTX in the winter in the late 90s when they simply did not seem work, but can't recall the production date on the MREs we were eating at the time.

[housil]

I remember one FTX in the winter in the late 90s when they simply did not seem work, but can't recall the production date on the MREs we were eating at the time.

Do you recall the temps?

I made the experience, that as colder it is, as poorer the FRH work once they are a little bit older. I tried to start a FRH with sow, that didn´t work either

[rattattoo]

I don't think the temperature could've had anything to do with the failures. It was a wonderful June night. Probably around 75°F

[Horsesoldier]

Do you recall the temps?

I made the experience, that as colder it is, as poorer the FRH work once they are a little bit older. I tried to start a FRH with sow, that didn´t work either

Nothing too extreme -- was probably right around freezing (+/- a few degrees in either direction) the whole time.

[noderaser]

Well, you're going to lose more heat into the environment when it's colder outside... It shouldn't make any difference for the chemical reaction. You might have to field-engineer yourself one of those reflective/insulated pouches to place the FRH inside.