A flameless ration heater, or FRH, is a water-activated exothermic chemical heater included with Meals, Ready-to-Eat (MREs), used to heat the food. US military specifications for the heater required that it be capable of raising the temperature of an 8 ounces (226.8 g) entree by 100 °F (56 °C) in twelve minutes, and that it has no visible flame.
The ration heater contains finely powdered iron and magnesium metals, and table salt. To activate the reaction, a small amount of water is added, and the boiling point of water is quickly reached as the reaction proceeds.
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