Flameless Chemical Heaters

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Magnesium heaters are in use with canned foods in Japan, HeaterMeals, the MountainHouse's Mountain Oven, Hot Pack, rations for NASA and US military and paramilitary MREs (Meals Ready to Eat). They provide a simple a safe method for heating food, with little risk of fire or explosion.

The most popular design uses heating pads made from a supercorrodible magnesium/iron alloy in a porous matrix formed from polymeric powders with sodium chloride incorporated with it or in a separate tablet. To heat, water is added either from an external source or by puncturing/tearing a container of water onto the heating pad. The water dissolves the sodium chloride into an electrolyte solution causing magnesium and iron to function as an anode and cathode, respectively. An exothermic oxidation-reduction reaction between the magnesium-iron alloy and water to produce magnesium hydroxide, hydrogen gas and heat.

Mg + 2H₂O ® Mg(OH)₂ + H₂ + Heat

To insure that the reaction doesn't prematurely occur while in storage, the heating pad must be kept in a watertight container protected from water and moist air. If the heater matrix is exposed to moist air at any time, its surface may become coated with a thin layer of insoluble magnesium hydroxide, which will hinder future chemical reactions. Heater pads that become wet in storage release hydrogen gas and can create a serious fire or explosion hazard that may ignite the very hot burning magnesium.

A different system is being developed by the US military called the Hydrogen-Free Ration Heater (HRH). It works by generating heat from the hydration of anhydride and neutralization of the hydrated products. The advantage of this system is that it doesn't create flammable hydrogen gas a a byproduct.

Advantages include:

no burns or forest fires from flames
unlikely to overcook or burn food
relatively non-toxic once used
some may be used as firestarter
unaffected by altitude

Disadvantages include:

weight, bulk
one time use only
produces a lot of garbage
limited to heating items in a sealed container
no easily found
may absorb water from air and become useless
produces hydrogen gas which can become explosive

Flameless Heaters

15oz Mountain House Mountain Oven Heater Kit (five pack)

Mountain House sells a flameless system for there dehydrated meals. It is composed of a resalable bag/oven, 5 heating pads, 5 salt tablets, a water bottle and a plastic bag.

0.7oz MRE Heater

A popular version is the one used by the US military in their MREs. These heating pads come in their own self-contained "waterproof" bags that are just large enough for a military MRE ration. These can be purchased in the US and Europe and are easy to find in US military surplus stores.

There are several generations of MRE flameless ration heaters and they can vary slightly. Some versions (generally older ones) come with a solid heater pad wrapped in cardboard, which can be used as very hot burning firestarters. Other versions have a flame resistant pouch contain the heater contents in powder form.

NOTE: Each US military MRE come with one ration heater, several well sealed items that are considered edible and a nice polystyrene spoon that isn't too brittle or heavy for backpacking use..

WARNING

Vapors released by activated heater contain hydrogen, a flammable gas.

Do not place an open flame in the vapor.

Vapors released by activated heater can displace oxygen.

When ten or more heaters are used inside a vehicle or shelter, ensure the ventilation system is operating or a top hatch or door is open.

Hot water leakage can burn and cause a cold- weather injury.

Use caution if carrying activated heater in pocket.

After heating, the heater bag and MRE pouch will be very hot.

Use caution when removing MRE pouch from bag.

Discard heater and bag after use.

Do not drink the water remaining in the bag or use it in food items.

HEATER AND ITS BYPRODUCTS ARE NOT INTENDED FOR HUMAN CONSUMPTION

OPERATING INSTRUCTIONS

SPECIAL INSTRUCTIONS FOR FROZEN MRE

Use two heaters: one to thaw, one to heat.
To thaw frozen MRE: Follow instructions below except, add water to bag before adding MRE. When heater begins to feel warm, add MRE to bag.
To heat thawed MRE: Follow instructions below.
In cold weather, heater can be placed in BDU pocket to heat MRE. Make sure folded end of bag is up to prevent water from leaking out.

1. Remove MRE pouch from carton and save carton.

2. Tear off top of bag. Place MRE pouch in bag with heater.

3. While holding MRE pouch and heater above lines on bag, pour water into bag until it reaches a level between lines. Slide heater and MRE to bottom of bag, and fold top of bag to side opposite heater.

4. With heater UNDERNEATH MRE, hold bag level for a minute to let heater soak up water.

5. Stuff assembly into carton with top of bag folded over top of MRE and heater underneath.

6. To prevent water from escaping and to maximize heat output, always keep:

HEATER located UNDERNEATH MRE;
BAG folded OVER TOP of MRE; and
CARTON INCLINED, with FOLDED END of bag UP.

After ten to fifteen minutes (depending on air temperature) top half of bag can be torn off and the MRE can be removed and eaten.

Knead MRE to ensure uniform temperature. CAUTION: The contents will be hot.

Zen Backpacking Stoves